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* [PATCH tip/core/rcu 01/40] rcu: Maintain special bits at bottom of ->dynticks counter
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
@ 2017-04-12 17:39 ` Paul E. McKenney
  2017-04-13  9:20   ` Peter Zijlstra
  2017-04-12 17:39 ` [PATCH tip/core/rcu 02/40] rcu: Make arch select smp_mb__after_unlock_lock() strength Paul E. McKenney
                   ` (39 subsequent siblings)
  40 siblings, 1 reply; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:39 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

Currently, IPIs are used to force other CPUs to invalidate their TLBs
in response to a kernel virtual-memory mapping change.  This works, but
degrades both battery lifetime (for idle CPUs) and real-time response
(for nohz_full CPUs), and in addition results in unnecessary IPIs due to
the fact that CPUs executing in usermode are unaffected by stale kernel
mappings.  It would be better to cause a CPU executing in usermode to
wait until it is entering kernel mode to do the flush, first to avoid
interrupting usemode tasks and second to handle multiple flush requests
with a single flush in the case of a long-running user task.

This commit therefore reserves a bit at the bottom of the ->dynticks
counter, which is checked upon exit from extended quiescent states.
If it is set, it is cleared and then a new rcu_eqs_special_exit() macro is
invoked, which, if not supplied, is an empty single-pass do-while loop.
If this bottom bit is set on -entry- to an extended quiescent state,
then a WARN_ON_ONCE() triggers.

This bottom bit may be set using a new rcu_eqs_special_set() function,
which returns true if the bit was set, or false if the CPU turned
out to not be in an extended quiescent state.  Please note that this
function refuses to set the bit for a non-nohz_full CPU when that CPU
is executing in usermode because usermode execution is tracked by RCU
as a dyntick-idle extended quiescent state only for nohz_full CPUs.

Reported-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcutiny.h |  5 ++++
 kernel/rcu/tree.c       | 73 +++++++++++++++++++++++++++++++++++++++----------
 kernel/rcu/tree.h       |  1 +
 3 files changed, 65 insertions(+), 14 deletions(-)

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index b452953e21c8..6c9d941e3962 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -33,6 +33,11 @@ static inline int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
 	return 0;
 }
 
+static inline bool rcu_eqs_special_set(int cpu)
+{
+	return false;  /* Never flag non-existent other CPUs! */
+}
+
 static inline unsigned long get_state_synchronize_rcu(void)
 {
 	return 0;
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 50fee7689e71..df8f6401f2d5 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -274,9 +274,19 @@ void rcu_bh_qs(void)
 
 static DEFINE_PER_CPU(int, rcu_sched_qs_mask);
 
+/*
+ * Steal a bit from the bottom of ->dynticks for idle entry/exit
+ * control.  Initially this is for TLB flushing.
+ */
+#define RCU_DYNTICK_CTRL_MASK 0x1
+#define RCU_DYNTICK_CTRL_CTR  (RCU_DYNTICK_CTRL_MASK + 1)
+#ifndef rcu_eqs_special_exit
+#define rcu_eqs_special_exit() do { } while (0)
+#endif
+
 static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
 	.dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
-	.dynticks = ATOMIC_INIT(1),
+	.dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR),
 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
 	.dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE,
 	.dynticks_idle = ATOMIC_INIT(1),
@@ -290,15 +300,20 @@ static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
 static void rcu_dynticks_eqs_enter(void)
 {
 	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
-	int special;
+	int seq;
 
 	/*
 	 * CPUs seeing atomic_inc_return() must see prior RCU read-side
 	 * critical sections, and we also must force ordering with the
 	 * next idle sojourn.
 	 */
-	special = atomic_inc_return(&rdtp->dynticks);
-	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && special & 0x1);
+	seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
+	/* Better be in an extended quiescent state! */
+	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
+		     (seq & RCU_DYNTICK_CTRL_CTR));
+	/* Better not have special action (TLB flush) pending! */
+	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
+		     (seq & RCU_DYNTICK_CTRL_MASK));
 }
 
 /*
@@ -308,15 +323,22 @@ static void rcu_dynticks_eqs_enter(void)
 static void rcu_dynticks_eqs_exit(void)
 {
 	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
-	int special;
+	int seq;
 
 	/*
 	 * CPUs seeing atomic_inc_return() must see prior idle sojourns,
 	 * and we also must force ordering with the next RCU read-side
 	 * critical section.
 	 */
-	special = atomic_inc_return(&rdtp->dynticks);
-	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(special & 0x1));
+	seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
+	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
+		     !(seq & RCU_DYNTICK_CTRL_CTR));
+	if (seq & RCU_DYNTICK_CTRL_MASK) {
+		atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdtp->dynticks);
+		smp_mb__after_atomic(); /* _exit after clearing mask. */
+		/* Prefer duplicate flushes to losing a flush. */
+		rcu_eqs_special_exit();
+	}
 }
 
 /*
@@ -333,9 +355,9 @@ static void rcu_dynticks_eqs_online(void)
 {
 	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
 
-	if (atomic_read(&rdtp->dynticks) & 0x1)
+	if (atomic_read(&rdtp->dynticks) & RCU_DYNTICK_CTRL_CTR)
 		return;
-	atomic_add(0x1, &rdtp->dynticks);
+	atomic_add(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
 }
 
 /*
@@ -347,7 +369,7 @@ bool rcu_dynticks_curr_cpu_in_eqs(void)
 {
 	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
 
-	return !(atomic_read(&rdtp->dynticks) & 0x1);
+	return !(atomic_read(&rdtp->dynticks) & RCU_DYNTICK_CTRL_CTR);
 }
 
 /*
@@ -358,7 +380,7 @@ int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
 {
 	int snap = atomic_add_return(0, &rdtp->dynticks);
 
-	return snap;
+	return snap & ~RCU_DYNTICK_CTRL_MASK;
 }
 
 /*
@@ -367,7 +389,7 @@ int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
  */
 static bool rcu_dynticks_in_eqs(int snap)
 {
-	return !(snap & 0x1);
+	return !(snap & RCU_DYNTICK_CTRL_CTR);
 }
 
 /*
@@ -387,10 +409,33 @@ static bool rcu_dynticks_in_eqs_since(struct rcu_dynticks *rdtp, int snap)
 static void rcu_dynticks_momentary_idle(void)
 {
 	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
-	int special = atomic_add_return(2, &rdtp->dynticks);
+	int special = atomic_add_return(2 * RCU_DYNTICK_CTRL_CTR,
+					&rdtp->dynticks);
 
 	/* It is illegal to call this from idle state. */
-	WARN_ON_ONCE(!(special & 0x1));
+	WARN_ON_ONCE(!(special & RCU_DYNTICK_CTRL_CTR));
+}
+
+/*
+ * Set the special (bottom) bit of the specified CPU so that it
+ * will take special action (such as flushing its TLB) on the
+ * next exit from an extended quiescent state.  Returns true if
+ * the bit was successfully set, or false if the CPU was not in
+ * an extended quiescent state.
+ */
+bool rcu_eqs_special_set(int cpu)
+{
+	int old;
+	int new;
+	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
+
+	do {
+		old = atomic_read(&rdtp->dynticks);
+		if (old & RCU_DYNTICK_CTRL_CTR)
+			return false;
+		new = old | RCU_DYNTICK_CTRL_MASK;
+	} while (atomic_cmpxchg(&rdtp->dynticks, old, new) != old);
+	return true;
 }
 
 DEFINE_PER_CPU_SHARED_ALIGNED(unsigned long, rcu_qs_ctr);
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index ec62a05bfdb3..7468b4de7e0c 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -596,6 +596,7 @@ extern struct rcu_state rcu_preempt_state;
 #endif /* #ifdef CONFIG_PREEMPT_RCU */
 
 int rcu_dynticks_snap(struct rcu_dynticks *rdtp);
+bool rcu_eqs_special_set(int cpu);
 
 #ifdef CONFIG_RCU_BOOST
 DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 02/40] rcu: Make arch select smp_mb__after_unlock_lock() strength
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
  2017-04-12 17:39 ` [PATCH tip/core/rcu 01/40] rcu: Maintain special bits at bottom of ->dynticks counter Paul E. McKenney
@ 2017-04-12 17:39 ` Paul E. McKenney
  2017-04-13  9:21   ` Peter Zijlstra
  2017-04-13  9:24   ` Peter Zijlstra
  2017-04-12 17:39 ` [PATCH tip/core/rcu 03/40] srcu: Consolidate batch checking into rcu_all_batches_empty() Paul E. McKenney
                   ` (38 subsequent siblings)
  40 siblings, 2 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:39 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney, Will Deacon, Boqun Feng,
	Benjamin Herrenschmidt, Paul Mackerras, linuxppc-dev

The definition of smp_mb__after_unlock_lock() is currently smp_mb()
for CONFIG_PPC and a no-op otherwise.  It would be better to instead
provide an architecture-selectable Kconfig option, and select the
strength of smp_mb__after_unlock_lock() based on that option.  This
commit therefore creates CONFIG_ARCH_WEAK_RELACQ, has PPC select it,
and bases the definition of smp_mb__after_unlock_lock() on this new
CONFIG_ARCH_WEAK_RELACQ Kconfig option.

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Boqun Feng <boqun.feng@linux.vnet.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: <linuxppc-dev@lists.ozlabs.org>
---
 arch/Kconfig             | 3 +++
 arch/powerpc/Kconfig     | 1 +
 include/linux/rcupdate.h | 6 +++---
 3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index cd211a14a88f..adefaf344239 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -320,6 +320,9 @@ config HAVE_CMPXCHG_LOCAL
 config HAVE_CMPXCHG_DOUBLE
 	bool
 
+config ARCH_WEAK_RELEASE_ACQUIRE
+	bool
+
 config ARCH_WANT_IPC_PARSE_VERSION
 	bool
 
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 97a8bc8a095c..7a5c9b764cd2 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -99,6 +99,7 @@ config PPC
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF		if PPC64
 	select ARCH_WANT_IPC_PARSE_VERSION
+	select ARCH_WEAK_RELEASE_ACQUIRE
 	select BINFMT_ELF
 	select BUILDTIME_EXTABLE_SORT
 	select CLONE_BACKWARDS
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index de88b33c0974..e6146d0074f8 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -1127,11 +1127,11 @@ do { \
  * if the UNLOCK and LOCK are executed by the same CPU or if the
  * UNLOCK and LOCK operate on the same lock variable.
  */
-#ifdef CONFIG_PPC
+#ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE
 #define smp_mb__after_unlock_lock()	smp_mb()  /* Full ordering for lock. */
-#else /* #ifdef CONFIG_PPC */
+#else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
 #define smp_mb__after_unlock_lock()	do { } while (0)
-#endif /* #else #ifdef CONFIG_PPC */
+#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
 
 
 #endif /* __LINUX_RCUPDATE_H */
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 03/40] srcu: Consolidate batch checking into rcu_all_batches_empty()
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
  2017-04-12 17:39 ` [PATCH tip/core/rcu 01/40] rcu: Maintain special bits at bottom of ->dynticks counter Paul E. McKenney
  2017-04-12 17:39 ` [PATCH tip/core/rcu 02/40] rcu: Make arch select smp_mb__after_unlock_lock() strength Paul E. McKenney
@ 2017-04-12 17:39 ` Paul E. McKenney
  2017-04-12 17:39 ` [PATCH tip/core/rcu 04/40] srcu: Check for tardy grace-period activity in cleanup_srcu_struct() Paul E. McKenney
                   ` (37 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:39 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The srcu_reschedule() function invokes rcu_batch_empty() on each of
the four rcu_batch structures in the srcu_struct in question twice.
Given that this check will also be needed in cleanup_srcu_struct(), this
commit consolidates these four checks into a new rcu_all_batches_empty()
function.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/srcu.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index ef3bcfb15b39..ba41a5d04b49 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -65,6 +65,17 @@ static inline bool rcu_batch_empty(struct rcu_batch *b)
 }
 
 /*
+ * Are all batches empty for the specified srcu_struct?
+ */
+static inline bool rcu_all_batches_empty(struct srcu_struct *sp)
+{
+	return rcu_batch_empty(&sp->batch_done) &&
+	       rcu_batch_empty(&sp->batch_check1) &&
+	       rcu_batch_empty(&sp->batch_check0) &&
+	       rcu_batch_empty(&sp->batch_queue);
+}
+
+/*
  * Remove the callback at the head of the specified rcu_batch structure
  * and return a pointer to it, or return NULL if the structure is empty.
  */
@@ -619,15 +630,9 @@ static void srcu_reschedule(struct srcu_struct *sp)
 {
 	bool pending = true;
 
-	if (rcu_batch_empty(&sp->batch_done) &&
-	    rcu_batch_empty(&sp->batch_check1) &&
-	    rcu_batch_empty(&sp->batch_check0) &&
-	    rcu_batch_empty(&sp->batch_queue)) {
+	if (rcu_all_batches_empty(sp)) {
 		spin_lock_irq(&sp->queue_lock);
-		if (rcu_batch_empty(&sp->batch_done) &&
-		    rcu_batch_empty(&sp->batch_check1) &&
-		    rcu_batch_empty(&sp->batch_check0) &&
-		    rcu_batch_empty(&sp->batch_queue)) {
+		if (rcu_all_batches_empty(sp)) {
 			sp->running = false;
 			pending = false;
 		}
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 04/40] srcu: Check for tardy grace-period activity in cleanup_srcu_struct()
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (2 preceding siblings ...)
  2017-04-12 17:39 ` [PATCH tip/core/rcu 03/40] srcu: Consolidate batch checking into rcu_all_batches_empty() Paul E. McKenney
@ 2017-04-12 17:39 ` Paul E. McKenney
  2017-04-12 17:39 ` [PATCH tip/core/rcu 05/40] rcu: Semicolon inside RCU_TRACE() for rcu.h Paul E. McKenney
                   ` (36 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:39 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

Users of SRCU are obliged to complete all grace-period activity before
invoking cleanup_srcu_struct().  This means that all calls to either
synchronize_srcu() or synchronize_srcu_expedited() must have returned,
and all calls to call_srcu() must have returned, and the last call to
call_srcu() must have been followed by a call to srcu_barrier().
Furthermore, the caller must have done something to prevent any
further calls to synchronize_srcu(), synchronize_srcu_expedited(),
and call_srcu().

Therefore, if there has ever been an invocation of call_srcu() on
the srcu_struct in question, the sequence of events must be as
follows:

1.  Prevent any further calls to call_srcu().
2.  Wait for any pre-existing call_srcu() invocations to return.
3.  Invoke srcu_barrier().
4.  It is now safe to invoke cleanup_srcu_struct().

On the other hand, if there has ever been a call to synchronize_srcu()
or synchronize_srcu_expedited(), the sequence of events must be as
follows:

1.  Prevent any further calls to synchronize_srcu() or
    synchronize_srcu_expedited().
2.  Wait for any pre-existing synchronize_srcu() or
    synchronize_srcu_expedited() invocations to return.
3.  It is now safe to invoke cleanup_srcu_struct().

If there have been calls to all both types of functions (call_srcu()
and either of synchronize_srcu() and synchronize_srcu_expedited()), then
the caller must do the first three steps of the call_srcu() procedure
above and the first two steps of the synchronize_s*() procedure above,
and only then invoke cleanup_srcu_struct().

Reported-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/srcu.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index ba41a5d04b49..6beeba7b0b67 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -261,6 +261,11 @@ void cleanup_srcu_struct(struct srcu_struct *sp)
 {
 	if (WARN_ON(srcu_readers_active(sp)))
 		return; /* Leakage unless caller handles error. */
+	if (WARN_ON(!rcu_all_batches_empty(sp)))
+		return; /* Leakage unless caller handles error. */
+	flush_delayed_work(&sp->work);
+	if (WARN_ON(sp->running))
+		return; /* Caller forgot to stop doing call_srcu()? */
 	free_percpu(sp->per_cpu_ref);
 	sp->per_cpu_ref = NULL;
 }
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 05/40] rcu: Semicolon inside RCU_TRACE() for rcu.h
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (3 preceding siblings ...)
  2017-04-12 17:39 ` [PATCH tip/core/rcu 04/40] srcu: Check for tardy grace-period activity in cleanup_srcu_struct() Paul E. McKenney
@ 2017-04-12 17:39 ` Paul E. McKenney
  2017-04-12 17:39 ` [PATCH tip/core/rcu 06/40] rcu: Semicolon inside RCU_TRACE() for Tiny RCU Paul E. McKenney
                   ` (35 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:39 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The current use of "RCU_TRACE(statement);" can cause odd bugs, especially
where "statement" is a local-variable declaration, as it can leave a
misplaced ";" in the source code.  This commit therefore converts these
to "RCU_TRACE(statement;)", which avoids the misplaced ";".

Reported-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcu.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 0d6ff3e471be..8700a81daf56 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -109,12 +109,12 @@ static inline bool __rcu_reclaim(const char *rn, struct rcu_head *head)
 
 	rcu_lock_acquire(&rcu_callback_map);
 	if (__is_kfree_rcu_offset(offset)) {
-		RCU_TRACE(trace_rcu_invoke_kfree_callback(rn, head, offset));
+		RCU_TRACE(trace_rcu_invoke_kfree_callback(rn, head, offset);)
 		kfree((void *)head - offset);
 		rcu_lock_release(&rcu_callback_map);
 		return true;
 	} else {
-		RCU_TRACE(trace_rcu_invoke_callback(rn, head));
+		RCU_TRACE(trace_rcu_invoke_callback(rn, head);)
 		head->func(head);
 		rcu_lock_release(&rcu_callback_map);
 		return false;
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 06/40] rcu: Semicolon inside RCU_TRACE() for Tiny RCU
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (4 preceding siblings ...)
  2017-04-12 17:39 ` [PATCH tip/core/rcu 05/40] rcu: Semicolon inside RCU_TRACE() for rcu.h Paul E. McKenney
@ 2017-04-12 17:39 ` Paul E. McKenney
  2017-04-12 17:39 ` [PATCH tip/core/rcu 07/40] rcu: Semicolon inside RCU_TRACE() for tree.c Paul E. McKenney
                   ` (34 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:39 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The current use of "RCU_TRACE(statement);" can cause odd bugs, especially
where "statement" is a local-variable declaration, as it can leave a
misplaced ";" in the source code.  This commit therefore converts these
to "RCU_TRACE(statement;)", which avoids the misplaced ";".

Reported-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tiny.c        | 20 ++++++++++----------
 kernel/rcu/tiny_plugin.h |  4 ++--
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index 6ad330dbbae2..e5385731e391 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -79,7 +79,7 @@ EXPORT_SYMBOL(__rcu_is_watching);
  */
 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
 {
-	RCU_TRACE(reset_cpu_stall_ticks(rcp));
+	RCU_TRACE(reset_cpu_stall_ticks(rcp);)
 	if (rcp->donetail != rcp->curtail) {
 		rcp->donetail = rcp->curtail;
 		return 1;
@@ -125,7 +125,7 @@ void rcu_bh_qs(void)
  */
 void rcu_check_callbacks(int user)
 {
-	RCU_TRACE(check_cpu_stalls());
+	RCU_TRACE(check_cpu_stalls();)
 	if (user)
 		rcu_sched_qs();
 	else if (!in_softirq())
@@ -143,7 +143,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 	const char *rn = NULL;
 	struct rcu_head *next, *list;
 	unsigned long flags;
-	RCU_TRACE(int cb_count = 0);
+	RCU_TRACE(int cb_count = 0;)
 
 	/* Move the ready-to-invoke callbacks to a local list. */
 	local_irq_save(flags);
@@ -152,7 +152,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 		local_irq_restore(flags);
 		return;
 	}
-	RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
+	RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1);)
 	list = rcp->rcucblist;
 	rcp->rcucblist = *rcp->donetail;
 	*rcp->donetail = NULL;
@@ -162,7 +162,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 	local_irq_restore(flags);
 
 	/* Invoke the callbacks on the local list. */
-	RCU_TRACE(rn = rcp->name);
+	RCU_TRACE(rn = rcp->name;)
 	while (list) {
 		next = list->next;
 		prefetch(next);
@@ -171,9 +171,9 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 		__rcu_reclaim(rn, list);
 		local_bh_enable();
 		list = next;
-		RCU_TRACE(cb_count++);
+		RCU_TRACE(cb_count++;)
 	}
-	RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
+	RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count);)
 	RCU_TRACE(trace_rcu_batch_end(rcp->name,
 				      cb_count, 0, need_resched(),
 				      is_idle_task(current),
@@ -221,7 +221,7 @@ static void __call_rcu(struct rcu_head *head,
 	local_irq_save(flags);
 	*rcp->curtail = head;
 	rcp->curtail = &head->next;
-	RCU_TRACE(rcp->qlen++);
+	RCU_TRACE(rcp->qlen++;)
 	local_irq_restore(flags);
 
 	if (unlikely(is_idle_task(current))) {
@@ -254,8 +254,8 @@ EXPORT_SYMBOL_GPL(call_rcu_bh);
 void __init rcu_init(void)
 {
 	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
-	RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk));
-	RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk));
+	RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk);)
+	RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk);)
 
 	rcu_early_boot_tests();
 }
diff --git a/kernel/rcu/tiny_plugin.h b/kernel/rcu/tiny_plugin.h
index c64b827ecbca..df3a60e19f07 100644
--- a/kernel/rcu/tiny_plugin.h
+++ b/kernel/rcu/tiny_plugin.h
@@ -162,8 +162,8 @@ static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
 
 static void check_cpu_stalls(void)
 {
-	RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
-	RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
+	RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk);)
+	RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk);)
 }
 
 #endif /* #ifdef CONFIG_RCU_TRACE */
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 07/40] rcu: Semicolon inside RCU_TRACE() for tree.c
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (5 preceding siblings ...)
  2017-04-12 17:39 ` [PATCH tip/core/rcu 06/40] rcu: Semicolon inside RCU_TRACE() for Tiny RCU Paul E. McKenney
@ 2017-04-12 17:39 ` Paul E. McKenney
  2017-04-12 17:39 ` [PATCH tip/core/rcu 08/40] rcu: Make call_rcu() do deferred NOCB wakeups Paul E. McKenney
                   ` (33 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:39 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The current use of "RCU_TRACE(statement);" can cause odd bugs, especially
where "statement" is a local-variable declaration, as it can leave a
misplaced ";" in the source code.  This commit therefore converts these
to "RCU_TRACE(statement;)", which avoids the misplaced ";".

Reported-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index df8f6401f2d5..e8843bf0f5e1 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2793,14 +2793,14 @@ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
  */
 static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
 {
-	RCU_TRACE(unsigned long mask);
-	RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda));
-	RCU_TRACE(struct rcu_node *rnp = rdp->mynode);
+	RCU_TRACE(unsigned long mask;)
+	RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda);)
+	RCU_TRACE(struct rcu_node *rnp = rdp->mynode;)
 
 	if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
 		return;
 
-	RCU_TRACE(mask = rdp->grpmask);
+	RCU_TRACE(mask = rdp->grpmask;)
 	trace_rcu_grace_period(rsp->name,
 			       rnp->gpnum + 1 - !!(rnp->qsmask & mask),
 			       TPS("cpuofl"));
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 08/40] rcu: Make call_rcu() do deferred NOCB wakeups
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (6 preceding siblings ...)
  2017-04-12 17:39 ` [PATCH tip/core/rcu 07/40] rcu: Semicolon inside RCU_TRACE() for tree.c Paul E. McKenney
@ 2017-04-12 17:39 ` Paul E. McKenney
  2017-04-12 17:39 ` [PATCH tip/core/rcu 09/40] rcu: Make rcu_all_qs() " Paul E. McKenney
                   ` (32 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:39 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

If a CONFIG_RCU_NOCB_CPUS kernel invokes call_rcu() with interrupts
disabled, wakeups must be deferred in order to avoid self-deadlock in the
cases where the disabled interrupts are due to scheduler locks being held.
In this case, a flag is set and is checked on entry to extended quiescent
states (usermode, idle), on exit from the RCU_SOFTIRQ handler, and when
the CPU in question goes offline.  However, a given CPU could avoid all
of those states for a considerable length of time.

This commit therefore allows a subsequent invocation of call_rcu() with
interrupts enabled to do the wakeup.  It also makes the wakeup function
clear the deferred-wakeup flag.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree_plugin.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 0a62a8f1caac..5a149091d262 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1768,6 +1768,7 @@ static void wake_nocb_leader(struct rcu_data *rdp, bool force)
 		return;
 	if (READ_ONCE(rdp_leader->nocb_leader_sleep) || force) {
 		/* Prior smp_mb__after_atomic() orders against prior enqueue. */
+		WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOGP_WAKE_NOT);
 		WRITE_ONCE(rdp_leader->nocb_leader_sleep, false);
 		swake_up(&rdp_leader->nocb_wq);
 	}
@@ -1853,7 +1854,9 @@ static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
 		return;
 	}
 	len = atomic_long_read(&rdp->nocb_q_count);
-	if (old_rhpp == &rdp->nocb_head) {
+	if (old_rhpp == &rdp->nocb_head ||
+	    (rcu_nocb_need_deferred_wakeup(rdp) &&
+	     !irqs_disabled_flags(flags))) {
 		if (!irqs_disabled_flags(flags)) {
 			/* ... if queue was empty ... */
 			wake_nocb_leader(rdp, false);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 09/40] rcu: Make rcu_all_qs() do deferred NOCB wakeups
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (7 preceding siblings ...)
  2017-04-12 17:39 ` [PATCH tip/core/rcu 08/40] rcu: Make call_rcu() do deferred NOCB wakeups Paul E. McKenney
@ 2017-04-12 17:39 ` Paul E. McKenney
  2017-04-12 17:39 ` [PATCH tip/core/rcu 10/40] rcu: Make rcu_note_context_switch() " Paul E. McKenney
                   ` (31 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:39 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

If a CONFIG_RCU_NOCB_CPUS kernel invokes call_rcu() with interrupts
disabled, wakeups must be deferred in order to avoid self-deadlock in
the cases where the disabled interrupts are due to scheduler locks being
held.  In this case, a flag is set and is checked on entry to extended
quiescent states (usermode, idle), on exit from the RCU_SOFTIRQ handler,
when the CPU in question goes offline, and on a subsequent invocation
of call_rcu().  However, a given CPU could avoid all of those states
for a considerable length of time.

This commit therefore allows an invocation of rcu_all_qs() to do the
wakeup.  It also makes the wakeup function clear the deferred-wakeup flag.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c        | 6 ++++++
 kernel/rcu/tree_plugin.h | 3 ++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index e8843bf0f5e1..eaa2b6d7abe2 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -522,6 +522,7 @@ EXPORT_SYMBOL_GPL(rcu_note_context_switch);
 void rcu_all_qs(void)
 {
 	unsigned long flags;
+	struct rcu_state *rsp;
 
 	barrier(); /* Avoid RCU read-side critical sections leaking down. */
 	if (unlikely(raw_cpu_read(rcu_sched_qs_mask))) {
@@ -544,6 +545,11 @@ void rcu_all_qs(void)
 		rcu_sched_qs();
 		preempt_enable();
 	}
+	for_each_rcu_flavor(rsp) {
+		preempt_disable();
+		do_nocb_deferred_wakeup(this_cpu_ptr(rsp->rda));
+		preempt_enable();
+	}
 	this_cpu_inc(rcu_qs_ctr);
 	barrier(); /* Avoid RCU read-side critical sections leaking up. */
 }
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 5a149091d262..0e2114e8076b 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2201,7 +2201,8 @@ static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
 {
 	int ndw;
 
-	if (!rcu_nocb_need_deferred_wakeup(rdp))
+	if (!rcu_nocb_need_deferred_wakeup(rdp) ||
+	    unlikely(rcu_scheduler_active != RCU_SCHEDULER_RUNNING))
 		return;
 	ndw = READ_ONCE(rdp->nocb_defer_wakeup);
 	WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOGP_WAKE_NOT);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 10/40] rcu: Make rcu_note_context_switch() do deferred NOCB wakeups
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (8 preceding siblings ...)
  2017-04-12 17:39 ` [PATCH tip/core/rcu 09/40] rcu: Make rcu_all_qs() " Paul E. McKenney
@ 2017-04-12 17:39 ` Paul E. McKenney
  2017-04-12 17:39 ` [PATCH tip/core/rcu 11/40] rcu: Pull rcu_sched_qs_mask into rcu_dynticks structure Paul E. McKenney
                   ` (30 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:39 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

If a CONFIG_RCU_NOCB_CPUS kernel invokes call_rcu() with interrupts
disabled, wakeups must be deferred in order to avoid self-deadlock in the
cases where the disabled interrupts are due to scheduler locks being held.
In this case, a flag is set and is checked on entry to extended quiescent
states (usermode, idle), on exit from the RCU_SOFTIRQ handler, when the
CPU in question goes offline, on a subsequent invocation of call_rcu(),
and from rcu_all_qs().  However, a given CPU could avoid all of those
states for a considerable length of time.

This commit therefore allows an invocation of rcu_note_context_switch()
to do the wakeup.  It also makes the wakeup function clear the
deferred-wakeup flag.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index eaa2b6d7abe2..7fa46967021f 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -495,12 +495,16 @@ static void rcu_momentary_dyntick_idle(void)
  */
 void rcu_note_context_switch(void)
 {
+	struct rcu_state *rsp;
+
 	barrier(); /* Avoid RCU read-side critical sections leaking down. */
 	trace_rcu_utilization(TPS("Start context switch"));
 	rcu_sched_qs();
 	rcu_preempt_note_context_switch();
 	if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
 		rcu_momentary_dyntick_idle();
+	for_each_rcu_flavor(rsp)
+		do_nocb_deferred_wakeup(this_cpu_ptr(rsp->rda));
 	trace_rcu_utilization(TPS("End context switch"));
 	barrier(); /* Avoid RCU read-side critical sections leaking up. */
 }
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 11/40] rcu: Pull rcu_sched_qs_mask into rcu_dynticks structure
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (9 preceding siblings ...)
  2017-04-12 17:39 ` [PATCH tip/core/rcu 10/40] rcu: Make rcu_note_context_switch() " Paul E. McKenney
@ 2017-04-12 17:39 ` Paul E. McKenney
  2017-04-12 17:39 ` [PATCH tip/core/rcu 12/40] rcu: Pull rcu_qs_ctr " Paul E. McKenney
                   ` (29 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:39 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The rcu_sched_qs_mask variable is yet another isolated per-CPU variable,
so this commit pulls it into the pre-existing rcu_dynticks per-CPU
structure.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 .../RCU/Design/Data-Structures/Data-Structures.html          |  9 ++++++++-
 kernel/rcu/tree.c                                            | 12 +++++-------
 kernel/rcu/tree.h                                            |  1 +
 3 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.html b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
index d583c653a703..bf7f266e8888 100644
--- a/Documentation/RCU/Design/Data-Structures/Data-Structures.html
+++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
@@ -1104,6 +1104,7 @@ Its fields are as follows:
   1   int dynticks_nesting;
   2   int dynticks_nmi_nesting;
   3   atomic_t dynticks;
+  4   int rcu_sched_qs_mask;
 </pre>
 
 <p>The <tt>-&gt;dynticks_nesting</tt> field counts the
@@ -1117,11 +1118,17 @@ NMIs are counted by the <tt>-&gt;dynticks_nmi_nesting</tt>
 field, except that NMIs that interrupt non-dyntick-idle execution
 are not counted.
 
-</p><p>Finally, the <tt>-&gt;dynticks</tt> field counts the corresponding
+</p><p>The <tt>-&gt;dynticks</tt> field counts the corresponding
 CPU's transitions to and from dyntick-idle mode, so that this counter
 has an even value when the CPU is in dyntick-idle mode and an odd
 value otherwise.
 
+</p><p>Finally, the  <tt>-&gt;rcu_sched_qs_mask</tt> field is used
+to record the fact that the RCU core code would really like to
+see a quiescent state from the corresponding CPU.
+This flag is checked by RCU's context-switch and <tt>cond_resched()</tt>
+code, which provide a momentary idle sojourn in response.
+
 <table>
 <tr><th>&nbsp;</th></tr>
 <tr><th align="left">Quick Quiz:</th></tr>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 7fa46967021f..315647d4e4cd 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -272,8 +272,6 @@ void rcu_bh_qs(void)
 	}
 }
 
-static DEFINE_PER_CPU(int, rcu_sched_qs_mask);
-
 /*
  * Steal a bit from the bottom of ->dynticks for idle entry/exit
  * control.  Initially this is for TLB flushing.
@@ -464,8 +462,8 @@ static void rcu_momentary_dyntick_idle(void)
 	 * Yes, we can lose flag-setting operations.  This is OK, because
 	 * the flag will be set again after some delay.
 	 */
-	resched_mask = raw_cpu_read(rcu_sched_qs_mask);
-	raw_cpu_write(rcu_sched_qs_mask, 0);
+	resched_mask = raw_cpu_read(rcu_dynticks.rcu_sched_qs_mask);
+	raw_cpu_write(rcu_dynticks.rcu_sched_qs_mask, 0);
 
 	/* Find the flavor that needs a quiescent state. */
 	for_each_rcu_flavor(rsp) {
@@ -501,7 +499,7 @@ void rcu_note_context_switch(void)
 	trace_rcu_utilization(TPS("Start context switch"));
 	rcu_sched_qs();
 	rcu_preempt_note_context_switch();
-	if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
+	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_sched_qs_mask)))
 		rcu_momentary_dyntick_idle();
 	for_each_rcu_flavor(rsp)
 		do_nocb_deferred_wakeup(this_cpu_ptr(rsp->rda));
@@ -529,7 +527,7 @@ void rcu_all_qs(void)
 	struct rcu_state *rsp;
 
 	barrier(); /* Avoid RCU read-side critical sections leaking down. */
-	if (unlikely(raw_cpu_read(rcu_sched_qs_mask))) {
+	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_sched_qs_mask))) {
 		local_irq_save(flags);
 		rcu_momentary_dyntick_idle();
 		local_irq_restore(flags);
@@ -1361,7 +1359,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 	 * is set too high, we override with half of the RCU CPU stall
 	 * warning delay.
 	 */
-	rcrmp = &per_cpu(rcu_sched_qs_mask, rdp->cpu);
+	rcrmp = &per_cpu(rcu_dynticks.rcu_sched_qs_mask, rdp->cpu);
 	if (time_after(jiffies, rdp->rsp->gp_start + jtsq) ||
 	    time_after(jiffies, rdp->rsp->jiffies_resched)) {
 		if (!(READ_ONCE(*rcrmp) & rdp->rsp->flavor_mask)) {
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 7468b4de7e0c..e298281984dc 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -113,6 +113,7 @@ struct rcu_dynticks {
 				    /* Process level is worth LLONG_MAX/2. */
 	int dynticks_nmi_nesting;   /* Track NMI nesting level. */
 	atomic_t dynticks;	    /* Even value for idle, else odd. */
+	int rcu_sched_qs_mask;      /* GP old, need quiescent state. */
 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
 	long long dynticks_idle_nesting;
 				    /* irq/process nesting level from idle. */
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 12/40] rcu: Pull rcu_qs_ctr into rcu_dynticks structure
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (10 preceding siblings ...)
  2017-04-12 17:39 ` [PATCH tip/core/rcu 11/40] rcu: Pull rcu_sched_qs_mask into rcu_dynticks structure Paul E. McKenney
@ 2017-04-12 17:39 ` Paul E. McKenney
  2017-04-12 17:39 ` [PATCH tip/core/rcu 13/40] rcu: Eliminate flavor scan in rcu_momentary_dyntick_idle() Paul E. McKenney
                   ` (28 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:39 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The rcu_qs_ctr variable is yet another isolated per-CPU variable,
so this commit pulls it into the pre-existing rcu_dynticks per-CPU
structure.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 .../RCU/Design/Data-Structures/Data-Structures.html       | 12 ++++++++++--
 kernel/rcu/tree.c                                         | 15 ++++++---------
 kernel/rcu/tree.h                                         |  3 ++-
 kernel/rcu/tree_trace.c                                   |  4 +---
 4 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.html b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
index bf7f266e8888..3d0311657533 100644
--- a/Documentation/RCU/Design/Data-Structures/Data-Structures.html
+++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
@@ -1105,6 +1105,7 @@ Its fields are as follows:
   2   int dynticks_nmi_nesting;
   3   atomic_t dynticks;
   4   int rcu_sched_qs_mask;
+  5   unsigned long rcu_qs_ctr;
 </pre>
 
 <p>The <tt>-&gt;dynticks_nesting</tt> field counts the
@@ -1123,12 +1124,19 @@ CPU's transitions to and from dyntick-idle mode, so that this counter
 has an even value when the CPU is in dyntick-idle mode and an odd
 value otherwise.
 
-</p><p>Finally, the  <tt>-&gt;rcu_sched_qs_mask</tt> field is used
+</p><p>The <tt>-&gt;rcu_sched_qs_mask</tt> field is used
 to record the fact that the RCU core code would really like to
-see a quiescent state from the corresponding CPU.
+see a quiescent state from the corresponding CPU, so much so that
+it is willing to call for heavy-weight dyntick-counter operations.
 This flag is checked by RCU's context-switch and <tt>cond_resched()</tt>
 code, which provide a momentary idle sojourn in response.
 
+</p><p>Finally the <tt>-&gt;rcu_qs_ctr</tt> field is used to record
+quiescent states from <tt>cond_resched()</tt>.
+Because <tt>cond_resched()</tt> can execute quite frequently, this
+must be quite lightweight, as in a non-atomic increment of this
+per-CPU field.
+
 <table>
 <tr><th>&nbsp;</th></tr>
 <tr><th align="left">Quick Quiz:</th></tr>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 315647d4e4cd..be40ebb4f0bf 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -436,9 +436,6 @@ bool rcu_eqs_special_set(int cpu)
 	return true;
 }
 
-DEFINE_PER_CPU_SHARED_ALIGNED(unsigned long, rcu_qs_ctr);
-EXPORT_PER_CPU_SYMBOL_GPL(rcu_qs_ctr);
-
 /*
  * Let the RCU core know that this CPU has gone through the scheduler,
  * which is a quiescent state.  This is called when the need for a
@@ -552,7 +549,7 @@ void rcu_all_qs(void)
 		do_nocb_deferred_wakeup(this_cpu_ptr(rsp->rda));
 		preempt_enable();
 	}
-	this_cpu_inc(rcu_qs_ctr);
+	this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
 	barrier(); /* Avoid RCU read-side critical sections leaking up. */
 }
 EXPORT_SYMBOL_GPL(rcu_all_qs);
@@ -1325,7 +1322,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 	 */
 	rnp = rdp->mynode;
 	if (time_after(jiffies, rdp->rsp->gp_start + jtsq) &&
-	    READ_ONCE(rdp->rcu_qs_ctr_snap) != per_cpu(rcu_qs_ctr, rdp->cpu) &&
+	    READ_ONCE(rdp->rcu_qs_ctr_snap) != per_cpu(rcu_dynticks.rcu_qs_ctr, rdp->cpu) &&
 	    READ_ONCE(rdp->gpnum) == rnp->gpnum && !rdp->gpwrap) {
 		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("rqc"));
 		return 1;
@@ -2034,7 +2031,7 @@ static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
 		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
 		need_gp = !!(rnp->qsmask & rdp->grpmask);
 		rdp->cpu_no_qs.b.norm = need_gp;
-		rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
+		rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr);
 		rdp->core_needs_qs = need_gp;
 		zero_cpu_stall_ticks(rdp);
 		WRITE_ONCE(rdp->gpwrap, false);
@@ -2632,7 +2629,7 @@ rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
 		 * within the current grace period.
 		 */
 		rdp->cpu_no_qs.b.norm = true;	/* need qs for new gp. */
-		rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
+		rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr);
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 		return;
 	}
@@ -3630,7 +3627,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
 	/* Is the RCU core waiting for a quiescent state from this CPU? */
 	if (rcu_scheduler_fully_active &&
 	    rdp->core_needs_qs && rdp->cpu_no_qs.b.norm &&
-	    rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) {
+	    rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_dynticks.rcu_qs_ctr)) {
 		rdp->n_rp_core_needs_qs++;
 	} else if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm) {
 		rdp->n_rp_report_qs++;
@@ -3943,7 +3940,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
 	rdp->gpnum = rnp->completed; /* Make CPU later note any new GP. */
 	rdp->completed = rnp->completed;
 	rdp->cpu_no_qs.b.norm = true;
-	rdp->rcu_qs_ctr_snap = per_cpu(rcu_qs_ctr, cpu);
+	rdp->rcu_qs_ctr_snap = per_cpu(rcu_dynticks.rcu_qs_ctr, cpu);
 	rdp->core_needs_qs = false;
 	trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index e298281984dc..76e4467bc765 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -113,7 +113,8 @@ struct rcu_dynticks {
 				    /* Process level is worth LLONG_MAX/2. */
 	int dynticks_nmi_nesting;   /* Track NMI nesting level. */
 	atomic_t dynticks;	    /* Even value for idle, else odd. */
-	int rcu_sched_qs_mask;      /* GP old, need quiescent state. */
+	int rcu_sched_qs_mask;      /* GP old, need heavy quiescent state. */
+	unsigned long rcu_qs_ctr;   /* Light universal quiescent state ctr. */
 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
 	long long dynticks_idle_nesting;
 				    /* irq/process nesting level from idle. */
diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c
index 8751a748499a..65b43be38e68 100644
--- a/kernel/rcu/tree_trace.c
+++ b/kernel/rcu/tree_trace.c
@@ -45,8 +45,6 @@
 #define RCU_TREE_NONCORE
 #include "tree.h"
 
-DECLARE_PER_CPU_SHARED_ALIGNED(unsigned long, rcu_qs_ctr);
-
 static int r_open(struct inode *inode, struct file *file,
 					const struct seq_operations *op)
 {
@@ -121,7 +119,7 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
 		   cpu_is_offline(rdp->cpu) ? '!' : ' ',
 		   ulong2long(rdp->completed), ulong2long(rdp->gpnum),
 		   rdp->cpu_no_qs.b.norm,
-		   rdp->rcu_qs_ctr_snap == per_cpu(rcu_qs_ctr, rdp->cpu),
+		   rdp->rcu_qs_ctr_snap == per_cpu(rdp->dynticks->rcu_qs_ctr, rdp->cpu),
 		   rdp->core_needs_qs);
 	seq_printf(m, " dt=%d/%llx/%d df=%lu",
 		   rcu_dynticks_snap(rdp->dynticks),
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 13/40] rcu: Eliminate flavor scan in rcu_momentary_dyntick_idle()
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (11 preceding siblings ...)
  2017-04-12 17:39 ` [PATCH tip/core/rcu 12/40] rcu: Pull rcu_qs_ctr " Paul E. McKenney
@ 2017-04-12 17:39 ` Paul E. McKenney
  2017-04-12 17:39 ` [PATCH tip/core/rcu 14/40] rcu: Place guard on rcu_all_qs() and rcu_note_context_switch() actions Paul E. McKenney
                   ` (27 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:39 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The rcu_momentary_dyntick_idle() function scans the RCU flavors, checking
that one of them still needs a quiescent state before doing an expensive
atomic operation on the ->dynticks counter.  However, this check reduces
overhead only after a rare race condition, and increases complexity.  This
commit therefore removes the scan and the mechanism enabling the scan.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 .../Design/Data-Structures/Data-Structures.html    |  4 +-
 kernel/rcu/tree.c                                  | 62 +++++-----------------
 kernel/rcu/tree.h                                  |  3 +-
 3 files changed, 15 insertions(+), 54 deletions(-)

diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.html b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
index 3d0311657533..e4bf20a68fa3 100644
--- a/Documentation/RCU/Design/Data-Structures/Data-Structures.html
+++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
@@ -1104,7 +1104,7 @@ Its fields are as follows:
   1   int dynticks_nesting;
   2   int dynticks_nmi_nesting;
   3   atomic_t dynticks;
-  4   int rcu_sched_qs_mask;
+  4   bool rcu_need_heavy_qs;
   5   unsigned long rcu_qs_ctr;
 </pre>
 
@@ -1124,7 +1124,7 @@ CPU's transitions to and from dyntick-idle mode, so that this counter
 has an even value when the CPU is in dyntick-idle mode and an odd
 value otherwise.
 
-</p><p>The <tt>-&gt;rcu_sched_qs_mask</tt> field is used
+</p><p>The <tt>-&gt;rcu_need_heavy_qs</tt> field is used
 to record the fact that the RCU core code would really like to
 see a quiescent state from the corresponding CPU, so much so that
 it is willing to call for heavy-weight dyntick-counter operations.
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index be40ebb4f0bf..e0c75488f30d 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -443,44 +443,14 @@ bool rcu_eqs_special_set(int cpu)
  * memory barriers to let the RCU core know about it, regardless of what
  * this CPU might (or might not) do in the near future.
  *
- * We inform the RCU core by emulating a zero-duration dyntick-idle
- * period, which we in turn do by incrementing the ->dynticks counter
- * by two.
+ * We inform the RCU core by emulating a zero-duration dyntick-idle period.
  *
  * The caller must have disabled interrupts.
  */
 static void rcu_momentary_dyntick_idle(void)
 {
-	struct rcu_data *rdp;
-	int resched_mask;
-	struct rcu_state *rsp;
-
-	/*
-	 * Yes, we can lose flag-setting operations.  This is OK, because
-	 * the flag will be set again after some delay.
-	 */
-	resched_mask = raw_cpu_read(rcu_dynticks.rcu_sched_qs_mask);
-	raw_cpu_write(rcu_dynticks.rcu_sched_qs_mask, 0);
-
-	/* Find the flavor that needs a quiescent state. */
-	for_each_rcu_flavor(rsp) {
-		rdp = raw_cpu_ptr(rsp->rda);
-		if (!(resched_mask & rsp->flavor_mask))
-			continue;
-		smp_mb(); /* rcu_sched_qs_mask before cond_resched_completed. */
-		if (READ_ONCE(rdp->mynode->completed) !=
-		    READ_ONCE(rdp->cond_resched_completed))
-			continue;
-
-		/*
-		 * Pretend to be momentarily idle for the quiescent state.
-		 * This allows the grace-period kthread to record the
-		 * quiescent state, with no need for this CPU to do anything
-		 * further.
-		 */
-		rcu_dynticks_momentary_idle();
-		break;
-	}
+	raw_cpu_write(rcu_dynticks.rcu_need_heavy_qs, false);
+	rcu_dynticks_momentary_idle();
 }
 
 /*
@@ -496,7 +466,7 @@ void rcu_note_context_switch(void)
 	trace_rcu_utilization(TPS("Start context switch"));
 	rcu_sched_qs();
 	rcu_preempt_note_context_switch();
-	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_sched_qs_mask)))
+	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs)))
 		rcu_momentary_dyntick_idle();
 	for_each_rcu_flavor(rsp)
 		do_nocb_deferred_wakeup(this_cpu_ptr(rsp->rda));
@@ -524,7 +494,7 @@ void rcu_all_qs(void)
 	struct rcu_state *rsp;
 
 	barrier(); /* Avoid RCU read-side critical sections leaking down. */
-	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_sched_qs_mask))) {
+	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs))) {
 		local_irq_save(flags);
 		rcu_momentary_dyntick_idle();
 		local_irq_restore(flags);
@@ -1285,7 +1255,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 				    bool *isidle, unsigned long *maxj)
 {
 	unsigned long jtsq;
-	int *rcrmp;
+	bool *rnhqp;
 	unsigned long rjtsc;
 	struct rcu_node *rnp;
 
@@ -1342,7 +1312,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 	 * in-kernel CPU-bound tasks cannot advance grace periods.
 	 * So if the grace period is old enough, make the CPU pay attention.
 	 * Note that the unsynchronized assignments to the per-CPU
-	 * rcu_sched_qs_mask variable are safe.  Yes, setting of
+	 * rcu_need_heavy_qs variable are safe.  Yes, setting of
 	 * bits can be lost, but they will be set again on the next
 	 * force-quiescent-state pass.  So lost bit sets do not result
 	 * in incorrect behavior, merely in a grace period lasting
@@ -1356,16 +1326,11 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 	 * is set too high, we override with half of the RCU CPU stall
 	 * warning delay.
 	 */
-	rcrmp = &per_cpu(rcu_dynticks.rcu_sched_qs_mask, rdp->cpu);
-	if (time_after(jiffies, rdp->rsp->gp_start + jtsq) ||
-	    time_after(jiffies, rdp->rsp->jiffies_resched)) {
-		if (!(READ_ONCE(*rcrmp) & rdp->rsp->flavor_mask)) {
-			WRITE_ONCE(rdp->cond_resched_completed,
-				   READ_ONCE(rdp->mynode->completed));
-			smp_mb(); /* ->cond_resched_completed before *rcrmp. */
-			WRITE_ONCE(*rcrmp,
-				   READ_ONCE(*rcrmp) + rdp->rsp->flavor_mask);
-		}
+	rnhqp = &per_cpu(rcu_dynticks.rcu_need_heavy_qs, rdp->cpu);
+	if (!READ_ONCE(*rnhqp) &&
+	    (time_after(jiffies, rdp->rsp->gp_start + jtsq) ||
+	     time_after(jiffies, rdp->rsp->jiffies_resched))) {
+		WRITE_ONCE(*rnhqp, true);
 		rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */
 	}
 
@@ -4179,7 +4144,6 @@ static void __init rcu_init_one(struct rcu_state *rsp)
 	static const char * const fqs[] = RCU_FQS_NAME_INIT;
 	static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
 	static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
-	static u8 fl_mask = 0x1;
 
 	int levelcnt[RCU_NUM_LVLS];		/* # nodes in each level. */
 	int levelspread[RCU_NUM_LVLS];		/* kids/node in each level. */
@@ -4201,8 +4165,6 @@ static void __init rcu_init_one(struct rcu_state *rsp)
 	for (i = 1; i < rcu_num_lvls; i++)
 		rsp->level[i] = rsp->level[i - 1] + levelcnt[i - 1];
 	rcu_init_levelspread(levelspread, levelcnt);
-	rsp->flavor_mask = fl_mask;
-	fl_mask <<= 1;
 
 	/* Initialize the elements themselves, starting from the leaves. */
 
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 76e4467bc765..b212cd0f22c7 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -113,7 +113,7 @@ struct rcu_dynticks {
 				    /* Process level is worth LLONG_MAX/2. */
 	int dynticks_nmi_nesting;   /* Track NMI nesting level. */
 	atomic_t dynticks;	    /* Even value for idle, else odd. */
-	int rcu_sched_qs_mask;      /* GP old, need heavy quiescent state. */
+	bool rcu_need_heavy_qs;      /* GP old, need heavy quiescent state. */
 	unsigned long rcu_qs_ctr;   /* Light universal quiescent state ctr. */
 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
 	long long dynticks_idle_nesting;
@@ -484,7 +484,6 @@ struct rcu_state {
 	struct rcu_node *level[RCU_NUM_LVLS + 1];
 						/* Hierarchy levels (+1 to */
 						/*  shut bogus gcc warning) */
-	u8 flavor_mask;				/* bit in flavor mask. */
 	struct rcu_data __percpu *rda;		/* pointer of percu rcu_data. */
 	call_rcu_func_t call;			/* call_rcu() flavor. */
 	int ncpus;				/* # CPUs seen so far. */
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 14/40] rcu: Place guard on rcu_all_qs() and rcu_note_context_switch() actions
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (12 preceding siblings ...)
  2017-04-12 17:39 ` [PATCH tip/core/rcu 13/40] rcu: Eliminate flavor scan in rcu_momentary_dyntick_idle() Paul E. McKenney
@ 2017-04-12 17:39 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 15/40] rcu: Default RCU_FANOUT_LEAF to 16 unless explicitly changed Paul E. McKenney
                   ` (26 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:39 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The rcu_all_qs() and rcu_note_context_switch() do a series of checks,
taking various actions to supply RCU with quiescent states, depending
on the outcomes of the various checks.  This is a bit much for scheduling
fastpaths, so this commit creates a separate ->rcu_urgent_qs field in
the rcu_dynticks structure that acts as a global guard for these checks.
Thus, in the common case, rcu_all_qs() and rcu_note_context_switch()
check the ->rcu_urgent_qs field, find it false, and simply return.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 .../Design/Data-Structures/Data-Structures.html    | 11 +++++-
 kernel/rcu/tree.c                                  | 43 +++++++++++++---------
 kernel/rcu/tree.h                                  |  3 +-
 kernel/rcu/tree_exp.h                              |  2 +
 kernel/rcu/tree_plugin.h                           |  8 +++-
 5 files changed, 45 insertions(+), 22 deletions(-)

diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.html b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
index e4bf20a68fa3..4dec89097559 100644
--- a/Documentation/RCU/Design/Data-Structures/Data-Structures.html
+++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
@@ -1106,6 +1106,7 @@ Its fields are as follows:
   3   atomic_t dynticks;
   4   bool rcu_need_heavy_qs;
   5   unsigned long rcu_qs_ctr;
+  6   bool rcu_urgent_qs;
 </pre>
 
 <p>The <tt>-&gt;dynticks_nesting</tt> field counts the
@@ -1131,12 +1132,20 @@ it is willing to call for heavy-weight dyntick-counter operations.
 This flag is checked by RCU's context-switch and <tt>cond_resched()</tt>
 code, which provide a momentary idle sojourn in response.
 
-</p><p>Finally the <tt>-&gt;rcu_qs_ctr</tt> field is used to record
+</p><p>The <tt>-&gt;rcu_qs_ctr</tt> field is used to record
 quiescent states from <tt>cond_resched()</tt>.
 Because <tt>cond_resched()</tt> can execute quite frequently, this
 must be quite lightweight, as in a non-atomic increment of this
 per-CPU field.
 
+</p><p>Finally, the <tt>-&gt;rcu_urgent_qs</tt> field is used to record
+the fact that the RCU core code would really like to see a quiescent
+state from the corresponding CPU, with the various other fields indicating
+just how badly RCU wants this quiescent state.
+This flag is checked by RCU's context-switch and <tt>cond_resched()</tt>
+code, which, if nothing else, non-atomically increment <tt>-&gt;rcu_qs_ctr</tt>
+in response.
+
 <table>
 <tr><th>&nbsp;</th></tr>
 <tr><th align="left">Quick Quiz:</th></tr>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index e0c75488f30d..ef4b8f63c06d 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -466,10 +466,16 @@ void rcu_note_context_switch(void)
 	trace_rcu_utilization(TPS("Start context switch"));
 	rcu_sched_qs();
 	rcu_preempt_note_context_switch();
+	/* Load rcu_urgent_qs before other flags. */
+	if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs)))
+		goto out;
+	this_cpu_write(rcu_dynticks.rcu_urgent_qs, false);
 	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs)))
 		rcu_momentary_dyntick_idle();
 	for_each_rcu_flavor(rsp)
 		do_nocb_deferred_wakeup(this_cpu_ptr(rsp->rda));
+	this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
+out:
 	trace_rcu_utilization(TPS("End context switch"));
 	barrier(); /* Avoid RCU read-side critical sections leaking up. */
 }
@@ -493,34 +499,28 @@ void rcu_all_qs(void)
 	unsigned long flags;
 	struct rcu_state *rsp;
 
+	if (!raw_cpu_read(rcu_dynticks.rcu_urgent_qs))
+		return;
+	preempt_disable();
+	/* Load rcu_urgent_qs before other flags. */
+	if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs))) {
+		preempt_enable();
+		return;
+	}
+	this_cpu_write(rcu_dynticks.rcu_urgent_qs, false);
 	barrier(); /* Avoid RCU read-side critical sections leaking down. */
 	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs))) {
 		local_irq_save(flags);
 		rcu_momentary_dyntick_idle();
 		local_irq_restore(flags);
 	}
-	if (unlikely(raw_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))) {
-		/*
-		 * Yes, we just checked a per-CPU variable with preemption
-		 * enabled, so we might be migrated to some other CPU at
-		 * this point.  That is OK because in that case, the
-		 * migration will supply the needed quiescent state.
-		 * We might end up needlessly disabling preemption and
-		 * invoking rcu_sched_qs() on the destination CPU, but
-		 * the probability and cost are both quite low, so this
-		 * should not be a problem in practice.
-		 */
-		preempt_disable();
+	if (unlikely(raw_cpu_read(rcu_sched_data.cpu_no_qs.b.exp)))
 		rcu_sched_qs();
-		preempt_enable();
-	}
-	for_each_rcu_flavor(rsp) {
-		preempt_disable();
+	for_each_rcu_flavor(rsp)
 		do_nocb_deferred_wakeup(this_cpu_ptr(rsp->rda));
-		preempt_enable();
-	}
 	this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
 	barrier(); /* Avoid RCU read-side critical sections leaking up. */
+	preempt_enable();
 }
 EXPORT_SYMBOL_GPL(rcu_all_qs);
 
@@ -1256,6 +1256,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 {
 	unsigned long jtsq;
 	bool *rnhqp;
+	bool *ruqp;
 	unsigned long rjtsc;
 	struct rcu_node *rnp;
 
@@ -1291,11 +1292,15 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 	 * might not be the case for nohz_full CPUs looping in the kernel.
 	 */
 	rnp = rdp->mynode;
+	ruqp = per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, rdp->cpu);
 	if (time_after(jiffies, rdp->rsp->gp_start + jtsq) &&
 	    READ_ONCE(rdp->rcu_qs_ctr_snap) != per_cpu(rcu_dynticks.rcu_qs_ctr, rdp->cpu) &&
 	    READ_ONCE(rdp->gpnum) == rnp->gpnum && !rdp->gpwrap) {
 		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("rqc"));
 		return 1;
+	} else {
+		/* Load rcu_qs_ctr before store to rcu_urgent_qs. */
+		smp_store_release(ruqp, true);
 	}
 
 	/* Check for the CPU being offline. */
@@ -1331,6 +1336,8 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 	    (time_after(jiffies, rdp->rsp->gp_start + jtsq) ||
 	     time_after(jiffies, rdp->rsp->jiffies_resched))) {
 		WRITE_ONCE(*rnhqp, true);
+		/* Store rcu_need_heavy_qs before rcu_urgent_qs. */
+		smp_store_release(ruqp, true);
 		rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */
 	}
 
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index b212cd0f22c7..d2f276fc2edc 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -113,8 +113,9 @@ struct rcu_dynticks {
 				    /* Process level is worth LLONG_MAX/2. */
 	int dynticks_nmi_nesting;   /* Track NMI nesting level. */
 	atomic_t dynticks;	    /* Even value for idle, else odd. */
-	bool rcu_need_heavy_qs;      /* GP old, need heavy quiescent state. */
+	bool rcu_need_heavy_qs;     /* GP old, need heavy quiescent state. */
 	unsigned long rcu_qs_ctr;   /* Light universal quiescent state ctr. */
+	bool rcu_urgent_qs;	    /* GP old need light quiescent state. */
 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
 	long long dynticks_idle_nesting;
 				    /* irq/process nesting level from idle. */
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index a7b639ccd46e..a1f52bbe9db6 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -331,6 +331,8 @@ static void sync_sched_exp_handler(void *data)
 		return;
 	}
 	__this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, true);
+	/* Store .exp before .rcu_urgent_qs. */
+	smp_store_release(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs), true);
 	resched_cpu(smp_processor_id());
 }
 
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 0e2114e8076b..4a9df7ea89a4 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1863,7 +1863,9 @@ static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
 			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
 					    TPS("WakeEmpty"));
 		} else {
-			rdp->nocb_defer_wakeup = RCU_NOGP_WAKE;
+			WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOGP_WAKE);
+			/* Store ->nocb_defer_wakeup before ->rcu_urgent_qs. */
+			smp_store_release(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs), true);
 			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
 					    TPS("WakeEmptyIsDeferred"));
 		}
@@ -1875,7 +1877,9 @@ static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
 			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
 					    TPS("WakeOvf"));
 		} else {
-			rdp->nocb_defer_wakeup = RCU_NOGP_WAKE_FORCE;
+			WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOGP_WAKE_FORCE);
+			/* Store ->nocb_defer_wakeup before ->rcu_urgent_qs. */
+			smp_store_release(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs), true);
 			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
 					    TPS("WakeOvfIsDeferred"));
 		}
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 15/40] rcu: Default RCU_FANOUT_LEAF to 16 unless explicitly changed
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (13 preceding siblings ...)
  2017-04-12 17:39 ` [PATCH tip/core/rcu 14/40] rcu: Place guard on rcu_all_qs() and rcu_note_context_switch() actions Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 16/40] srcu: Abstract multi-tail callback list handling Paul E. McKenney
                   ` (25 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

If the RCU_EXPERT Kconfig option is not set (the default), then the
RCU_FANOUT_LEAF Kconfig option will not be defined, which will cause
the leaf-level rcu_node tree fanout to default to 32 on 32-bit systems
and 64 on 64-bit systems.  This can result in excessive lock contention.
This commit therefore changes the computation of the leaf-level rcu_node
tree fanout so that the result will be 16 unless an explicit Kconfig or
kernel-boot setting says otherwise.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.h | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index d2f276fc2edc..376c01e539c7 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -52,11 +52,7 @@
 #ifdef CONFIG_RCU_FANOUT_LEAF
 #define RCU_FANOUT_LEAF CONFIG_RCU_FANOUT_LEAF
 #else /* #ifdef CONFIG_RCU_FANOUT_LEAF */
-# ifdef CONFIG_64BIT
-# define RCU_FANOUT_LEAF 64
-# else
-# define RCU_FANOUT_LEAF 32
-# endif
+#define RCU_FANOUT_LEAF 16
 #endif /* #else #ifdef CONFIG_RCU_FANOUT_LEAF */
 
 #define RCU_FANOUT_1	      (RCU_FANOUT_LEAF)
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 16/40] srcu: Abstract multi-tail callback list handling
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (14 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 15/40] rcu: Default RCU_FANOUT_LEAF to 16 unless explicitly changed Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 17/40] srcu: Allow SRCU to access rcu_scheduler_active Paul E. McKenney
                   ` (24 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

RCU has only one multi-tail callback list, which is implemented via
the nxtlist, nxttail, nxtcompleted, qlen_lazy, and qlen fields in the
rcu_data structure, and whose operations are open-code throughout the
Tree RCU implementation.  This has been more or less OK in the past,
but upcoming callback-list optimizations in SRCU could really use
a multi-tail callback list there as well.

This commit therefore abstracts the multi-tail callback list handling
into a new kernel/rcu/rcu_segcblist.h file, and uses this new API.
The simple head-and-tail pointer callback list is also abstracted and
applied everywhere except for the NOCB callback-offload lists.  (Yes,
the plan is to apply them there as well, but this commit is already
bigger than would be good.)

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcu_segcblist.h | 626 +++++++++++++++++++++++++++++++++++++++++++++
 kernel/rcu/tree.c          | 348 ++++++++-----------------
 kernel/rcu/tree.h          |  41 +--
 kernel/rcu/tree_plugin.h   |  54 ++--
 kernel/rcu/tree_trace.c    |  21 +-
 5 files changed, 781 insertions(+), 309 deletions(-)
 create mode 100644 kernel/rcu/rcu_segcblist.h

diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
new file mode 100644
index 000000000000..55b20ab5f940
--- /dev/null
+++ b/kernel/rcu/rcu_segcblist.h
@@ -0,0 +1,626 @@
+/*
+ * RCU segmented callback lists
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright IBM Corporation, 2017
+ *
+ * Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ */
+
+#ifndef __KERNEL_RCU_SEGCBLIST_H
+#define __KERNEL_RCU_SEGCBLIST_H
+
+/* Simple unsegmented callback lists. */
+struct rcu_cblist {
+	struct rcu_head *head;
+	struct rcu_head **tail;
+	long len;
+	long len_lazy;
+};
+
+#define RCU_CBLIST_INITIALIZER(n) { .head = NULL, .tail = &n.head }
+
+/* Initialize simple callback list. */
+static inline void rcu_cblist_init(struct rcu_cblist *rclp)
+{
+	rclp->head = NULL;
+	rclp->tail = &rclp->head;
+	rclp->len = 0;
+	rclp->len_lazy = 0;
+}
+
+/* Is simple callback list empty? */
+static inline bool rcu_cblist_empty(struct rcu_cblist *rclp)
+{
+	return !rclp->head;
+}
+
+/* Return number of callbacks in simple callback list. */
+static inline long rcu_cblist_n_cbs(struct rcu_cblist *rclp)
+{
+	return rclp->len;
+}
+
+/* Return number of lazy callbacks in simple callback list. */
+static inline long rcu_cblist_n_lazy_cbs(struct rcu_cblist *rclp)
+{
+	return rclp->len_lazy;
+}
+
+/*
+ * Debug function to actually count the number of callbacks.
+ * If the number exceeds the limit specified, return -1.
+ */
+static inline long rcu_cblist_count_cbs(struct rcu_cblist *rclp, long lim)
+{
+	int cnt = 0;
+	struct rcu_head **rhpp = &rclp->head;
+
+	for (;;) {
+		if (!*rhpp)
+			return cnt;
+		if (++cnt > lim)
+			return -1;
+		rhpp = &(*rhpp)->next;
+	}
+}
+
+/*
+ * Dequeue the oldest rcu_head structure from the specified callback
+ * list.  This function assumes that the callback is non-lazy, but
+ * the caller can later invoke rcu_cblist_dequeued_lazy() if it
+ * finds otherwise (and if it cares about laziness).  This allows
+ * different users to have different ways of determining laziness.
+ */
+static inline struct rcu_head *rcu_cblist_dequeue(struct rcu_cblist *rclp)
+{
+	struct rcu_head *rhp;
+
+	rhp = rclp->head;
+	if (!rhp)
+		return NULL;
+	prefetch(rhp);
+	rclp->len--;
+	rclp->head = rhp->next;
+	if (!rclp->head)
+		rclp->tail = &rclp->head;
+	return rhp;
+}
+
+/*
+ * Account for the fact that a previously dequeued callback turned out
+ * to be marked as lazy.
+ */
+static inline void rcu_cblist_dequeued_lazy(struct rcu_cblist *rclp)
+{
+	rclp->len_lazy--;
+}
+
+/*
+ * Interim function to return rcu_cblist head pointer.  Longer term, the
+ * rcu_cblist will be used more pervasively, removing the need for this
+ * function.
+ */
+static inline struct rcu_head *rcu_cblist_head(struct rcu_cblist *rclp)
+{
+	return rclp->head;
+}
+
+/*
+ * Interim function to return rcu_cblist head pointer.  Longer term, the
+ * rcu_cblist will be used more pervasively, removing the need for this
+ * function.
+ */
+static inline struct rcu_head **rcu_cblist_tail(struct rcu_cblist *rclp)
+{
+	WARN_ON_ONCE(rcu_cblist_empty(rclp));
+	return rclp->tail;
+}
+
+/* Complicated segmented callback lists.  ;-) */
+
+/*
+ * Index values for segments in rcu_segcblist structure.
+ *
+ * The segments are as follows:
+ *
+ * [head, *tails[RCU_DONE_TAIL]):
+ *	Callbacks whose grace period has elapsed, and thus can be invoked.
+ * [*tails[RCU_DONE_TAIL], *tails[RCU_WAIT_TAIL]):
+ *	Callbacks waiting for the current GP from the current CPU's viewpoint.
+ * [*tails[RCU_WAIT_TAIL], *tails[RCU_NEXT_READY_TAIL]):
+ *	Callbacks that arrived before the next GP started, again from
+ *	the current CPU's viewpoint.  These can be handled by the next GP.
+ * [*tails[RCU_NEXT_READY_TAIL], *tails[RCU_NEXT_TAIL]):
+ *	Callbacks that might have arrived after the next GP started.
+ *	There is some uncertainty as to when a given GP starts and
+ *	ends, but a CPU knows the exact times if it is the one starting
+ *	or ending the GP.  Other CPUs know that the previous GP ends
+ *	before the next one starts.
+ *
+ * Note that RCU_WAIT_TAIL cannot be empty unless RCU_NEXT_READY_TAIL is also
+ * empty.
+ *
+ * The ->gp_seq[] array contains the grace-period number at which the
+ * corresponding segment of callbacks will be ready to invoke.  A given
+ * element of this array is meaningful only when the corresponding segment
+ * is non-empty, and it is never valid for RCU_DONE_TAIL (whose callbacks
+ * are already ready to invoke) or for RCU_NEXT_TAIL (whose callbacks have
+ * not yet been assigned a grace-period number).
+ */
+#define RCU_DONE_TAIL		0	/* Also RCU_WAIT head. */
+#define RCU_WAIT_TAIL		1	/* Also RCU_NEXT_READY head. */
+#define RCU_NEXT_READY_TAIL	2	/* Also RCU_NEXT head. */
+#define RCU_NEXT_TAIL		3
+#define RCU_CBLIST_NSEGS	4
+
+struct rcu_segcblist {
+	struct rcu_head *head;
+	struct rcu_head **tails[RCU_CBLIST_NSEGS];
+	unsigned long gp_seq[RCU_CBLIST_NSEGS];
+	long len;
+	long len_lazy;
+};
+
+/*
+ * Initialize an rcu_segcblist structure.
+ */
+static inline void rcu_segcblist_init(struct rcu_segcblist *rsclp)
+{
+	int i;
+
+	BUILD_BUG_ON(RCU_NEXT_TAIL + 1 != ARRAY_SIZE(rsclp->gp_seq));
+	BUILD_BUG_ON(ARRAY_SIZE(rsclp->tails) != ARRAY_SIZE(rsclp->gp_seq));
+	rsclp->head = NULL;
+	for (i = 0; i < RCU_CBLIST_NSEGS; i++)
+		rsclp->tails[i] = &rsclp->head;
+	rsclp->len = 0;
+	rsclp->len_lazy = 0;
+}
+
+/*
+ * Is the specified rcu_segcblist structure empty?
+ *
+ * But careful!  The fact that the ->head field is NULL does not
+ * necessarily imply that there are no callbacks associated with
+ * this structure.  When callbacks are being invoked, they are
+ * removed as a group.  If callback invocation must be preempted,
+ * the remaining callbacks will be added back to the list.  Either
+ * way, the counts are updated later.
+ *
+ * So it is often the case that rcu_segcblist_n_cbs() should be used
+ * instead.
+ */
+static inline bool rcu_segcblist_empty(struct rcu_segcblist *rsclp)
+{
+	return !rsclp->head;
+}
+
+/* Return number of callbacks in segmented callback list. */
+static inline long rcu_segcblist_n_cbs(struct rcu_segcblist *rsclp)
+{
+	return READ_ONCE(rsclp->len);
+}
+
+/* Return number of lazy callbacks in segmented callback list. */
+static inline long rcu_segcblist_n_lazy_cbs(struct rcu_segcblist *rsclp)
+{
+	return rsclp->len_lazy;
+}
+
+/* Return number of lazy callbacks in segmented callback list. */
+static inline long rcu_segcblist_n_nonlazy_cbs(struct rcu_segcblist *rsclp)
+{
+	return rsclp->len - rsclp->len_lazy;
+}
+
+/*
+ * Is the specified rcu_segcblist enabled, for example, not corresponding
+ * to an offline or callback-offloaded CPU?
+ */
+static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp)
+{
+	return !!rsclp->tails[RCU_NEXT_TAIL];
+}
+
+/*
+ * Disable the specified rcu_segcblist structure, so that callbacks can
+ * no longer be posted to it.  This structure must be empty.
+ */
+static inline void rcu_segcblist_disable(struct rcu_segcblist *rsclp)
+{
+	WARN_ON_ONCE(!rcu_segcblist_empty(rsclp));
+	WARN_ON_ONCE(rcu_segcblist_n_cbs(rsclp));
+	WARN_ON_ONCE(rcu_segcblist_n_lazy_cbs(rsclp));
+	rsclp->tails[RCU_NEXT_TAIL] = NULL;
+}
+
+/*
+ * Is the specified segment of the specified rcu_segcblist structure
+ * empty of callbacks?
+ */
+static inline bool rcu_segcblist_segempty(struct rcu_segcblist *rsclp, int seg)
+{
+	if (seg == RCU_DONE_TAIL)
+		return &rsclp->head == rsclp->tails[RCU_DONE_TAIL];
+	return rsclp->tails[seg - 1] == rsclp->tails[seg];
+}
+
+/*
+ * Are all segments following the specified segment of the specified
+ * rcu_segcblist structure empty of callbacks?  (The specified
+ * segment might well contain callbacks.)
+ */
+static inline bool rcu_segcblist_restempty(struct rcu_segcblist *rsclp, int seg)
+{
+	return !*rsclp->tails[seg];
+}
+
+/*
+ * Does the specified rcu_segcblist structure contain callbacks that
+ * are ready to be invoked?
+ */
+static inline bool rcu_segcblist_ready_cbs(struct rcu_segcblist *rsclp)
+{
+	return rcu_segcblist_is_enabled(rsclp) &&
+	       &rsclp->head != rsclp->tails[RCU_DONE_TAIL];
+}
+
+/*
+ * Does the specified rcu_segcblist structure contain callbacks that
+ * are still pending, that is, not yet ready to be invoked?
+ */
+static inline bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp)
+{
+	return rcu_segcblist_is_enabled(rsclp) &&
+	       !rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL);
+}
+
+/*
+ * Return a pointer to the first callback in the specified rcu_segcblist
+ * structure.  This is useful for diagnostics.
+ */
+static inline struct rcu_head *
+rcu_segcblist_first_cb(struct rcu_segcblist *rsclp)
+{
+	if (rcu_segcblist_is_enabled(rsclp))
+	       return rsclp->head;
+	return NULL;
+}
+
+/*
+ * Return a pointer to the first pending callback in the specified
+ * rcu_segcblist structure.  This is useful just after posting a given
+ * callback -- if that callback is the first pending callback, then
+ * you cannot rely on someone else having already started up the required
+ * grace period.
+ */
+static inline struct rcu_head *
+rcu_segcblist_first_pend_cb(struct rcu_segcblist *rsclp)
+{
+	if (rcu_segcblist_is_enabled(rsclp))
+	       return *rsclp->tails[RCU_DONE_TAIL];
+	return NULL;
+}
+
+/*
+ * Does the specified rcu_segcblist structure contain callbacks that
+ * have not yet been processed beyond having been posted, that is,
+ * does it contain callbacks in its last segment?
+ */
+static inline bool rcu_segcblist_new_cbs(struct rcu_segcblist *rsclp)
+{
+	return rcu_segcblist_is_enabled(rsclp) &&
+	       !rcu_segcblist_restempty(rsclp, RCU_NEXT_READY_TAIL);
+}
+
+/*
+ * Enqueue the specified callback onto the specified rcu_segcblist
+ * structure, updating accounting as needed.  Note that the ->len
+ * field may be accessed locklessly, hence the WRITE_ONCE().
+ * The ->len field is used by rcu_barrier() and friends to determine
+ * if it must post a callback on this structure, and it is OK
+ * for rcu_barrier() to sometimes post callbacks needlessly, but
+ * absolutely not OK for it to ever miss posting a callback.
+ */
+static inline void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
+					 struct rcu_head *rhp, bool lazy)
+{
+	WRITE_ONCE(rsclp->len, rsclp->len + 1); /* ->len sampled locklessly. */
+	if (lazy)
+		rsclp->len_lazy++;
+	smp_mb(); /* Ensure counts are updated before callback is enqueued. */
+	rhp->next = NULL;
+	*rsclp->tails[RCU_NEXT_TAIL] = rhp;
+	rsclp->tails[RCU_NEXT_TAIL] = &rhp->next;
+}
+
+/*
+ * Extract only the counts from the specified rcu_segcblist structure,
+ * and place them in the specified rcu_cblist structure.  This function
+ * supports both callback orphaning and invocation, hence the separation
+ * of counts and callbacks.  (Callbacks ready for invocation must be
+ * orphaned and adopted separately from pending callbacks, but counts
+ * apply to all callbacks.  Locking must be used to make sure that
+ * both orphaned-callbacks lists are consistent.)
+ */
+static inline void rcu_segcblist_extract_count(struct rcu_segcblist *rsclp,
+					       struct rcu_cblist *rclp)
+{
+	rclp->len_lazy += rsclp->len_lazy;
+	rclp->len += rsclp->len;
+	rsclp->len_lazy = 0;
+	WRITE_ONCE(rsclp->len, 0); /* ->len sampled locklessly. */
+}
+
+/*
+ * Extract only those callbacks ready to be invoked from the specified
+ * rcu_segcblist structure and place them in the specified rcu_cblist
+ * structure.
+ */
+static inline void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp,
+						  struct rcu_cblist *rclp)
+{
+	int i;
+
+	if (!rcu_segcblist_ready_cbs(rsclp))
+		return; /* Nothing to do. */
+	*rclp->tail = rsclp->head;
+	rsclp->head = *rsclp->tails[RCU_DONE_TAIL];
+	*rsclp->tails[RCU_DONE_TAIL] = NULL;
+	rclp->tail = rsclp->tails[RCU_DONE_TAIL];
+	for (i = RCU_CBLIST_NSEGS - 1; i >= RCU_DONE_TAIL; i--)
+		if (rsclp->tails[i] == rsclp->tails[RCU_DONE_TAIL])
+			rsclp->tails[i] = &rsclp->head;
+}
+
+/*
+ * Extract only those callbacks still pending (not yet ready to be
+ * invoked) from the specified rcu_segcblist structure and place them in
+ * the specified rcu_cblist structure.  Note that this loses information
+ * about any callbacks that might have been partway done waiting for
+ * their grace period.  Too bad!  They will have to start over.
+ */
+static inline void
+rcu_segcblist_extract_pend_cbs(struct rcu_segcblist *rsclp,
+			       struct rcu_cblist *rclp)
+{
+	int i;
+
+	if (!rcu_segcblist_pend_cbs(rsclp))
+		return; /* Nothing to do. */
+	*rclp->tail = *rsclp->tails[RCU_DONE_TAIL];
+	rclp->tail = rsclp->tails[RCU_NEXT_TAIL];
+	*rsclp->tails[RCU_DONE_TAIL] = NULL;
+	for (i = RCU_DONE_TAIL + 1; i < RCU_CBLIST_NSEGS; i++)
+		rsclp->tails[i] = rsclp->tails[RCU_DONE_TAIL];
+}
+
+/*
+ * Move the entire contents of the specified rcu_segcblist structure,
+ * counts, callbacks, and all, to the specified rcu_cblist structure.
+ * @@@ Why do we need this???  Moving early-boot CBs to NOCB lists?
+ * @@@ Memory barrier needed?  (Not if only used at boot time...)
+ */
+static inline void rcu_segcblist_extract_all(struct rcu_segcblist *rsclp,
+					     struct rcu_cblist *rclp)
+{
+	rcu_segcblist_extract_done_cbs(rsclp, rclp);
+	rcu_segcblist_extract_pend_cbs(rsclp, rclp);
+	rcu_segcblist_extract_count(rsclp, rclp);
+}
+
+/*
+ * Insert counts from the specified rcu_cblist structure in the
+ * specified rcu_segcblist structure.
+ */
+static inline void rcu_segcblist_insert_count(struct rcu_segcblist *rsclp,
+					      struct rcu_cblist *rclp)
+{
+	
+	rsclp->len_lazy += rclp->len_lazy;
+	/* ->len sampled locklessly. */
+	WRITE_ONCE(rsclp->len, rsclp->len + rclp->len);
+	rclp->len_lazy = 0;
+	rclp->len = 0;
+}
+
+/*
+ * Move callbacks from the specified rcu_cblist to the beginning of the
+ * done-callbacks segment of the specified rcu_segcblist.
+ */
+static inline void rcu_segcblist_insert_done_cbs(struct rcu_segcblist *rsclp,
+						 struct rcu_cblist *rclp)
+{
+	int i;
+
+	if (!rclp->head)
+		return; /* No callbacks to move. */
+	*rclp->tail = rsclp->head;
+	rsclp->head = rclp->head;
+	for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++)
+		if (&rsclp->head == rsclp->tails[i])
+			rsclp->tails[i] = rclp->tail;
+		else
+			break;
+	rclp->head = NULL;
+	rclp->tail = &rclp->head;
+}
+
+/*
+ * Move callbacks from the specified rcu_cblist to the end of the
+ * new-callbacks segment of the specified rcu_segcblist.
+ */
+static inline void rcu_segcblist_insert_pend_cbs(struct rcu_segcblist *rsclp,
+						 struct rcu_cblist *rclp)
+{
+	if (!rclp->head)
+		return; /* Nothing to do. */
+	*rsclp->tails[RCU_NEXT_TAIL] = rclp->head;
+	rsclp->tails[RCU_NEXT_TAIL] = rclp->tail;
+	rclp->head = NULL;
+	rclp->tail = &rclp->head;
+}
+
+/*
+ * Advance the callbacks in the specified rcu_segcblist structure based
+ * on the current value passed in for the grace-period counter.
+ */
+static inline void rcu_segcblist_advance(struct rcu_segcblist *rsclp,
+					 unsigned long seq)
+{
+	int i, j;
+
+	WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
+	WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL));
+
+	/*
+	 * Find all callbacks whose ->gp_seq numbers indicate that they
+	 * are ready to invoke, and put them into the RCU_DONE_TAIL segment.
+	 */
+	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
+		if (ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
+			break;
+		rsclp->tails[RCU_DONE_TAIL] = rsclp->tails[i];
+	}
+
+	/* If no callbacks moved, nothing more need be done. */
+	if (i == RCU_WAIT_TAIL)
+		return;
+
+	/* Clean up tail pointers that might have been misordered above. */
+	for (j = RCU_WAIT_TAIL; j < i; j++)
+		rsclp->tails[j] = rsclp->tails[RCU_DONE_TAIL];
+
+	/*
+	 * Callbacks moved, so clean up the misordered ->tails[] pointers
+	 * that now point into the middle of the list of ready-to-invoke
+	 * callbacks.  The overall effect is to copy down the later pointers
+	 * into the gap that was created by the now-ready segments.
+	 */
+	for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
+		if (rsclp->tails[j] == rsclp->tails[RCU_NEXT_TAIL])
+			break;  /* No more callbacks. */
+		rsclp->tails[j] = rsclp->tails[i];
+		rsclp->gp_seq[j] = rsclp->gp_seq[i];
+	}
+}
+
+/*
+ * "Accelerate" callbacks based on more-accurate grace-period information.
+ * The reason for this is that RCU does not synchronize the beginnings and
+ * ends of grace periods, and that callbacks are posted locally.  This in
+ * turn means that the callbacks must be labelled conservatively early
+ * on, as getting exact information would degrade both performance and
+ * scalability.  When more accurate grace-period information becomes
+ * available, previously posted callbacks can be "accelerated", marking
+ * them to complete at the end of the earlier grace period.
+ *
+ * This function operates on an rcu_segcblist structure, and also the
+ * grace-period sequence number at which new callbacks would become
+ * ready to invoke.
+ */
+static inline bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp,
+					    unsigned long seq)
+{
+	int i;
+
+	WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
+	WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL));
+
+	/*
+	 * Find the segment preceding the oldest segment of callbacks
+	 * whose ->gp_seq[] completion is at or after that passed in via
+	 * "seq", skipping any empty segments.  This oldest segment, along
+	 * with any later segments, can be merged in with any newly arrived
+	 * callbacks in the RCU_NEXT_TAIL segment, and assigned "seq"
+	 * as their ->gp_seq[] grace-period completion sequence number.
+	 */
+	for (i = RCU_NEXT_READY_TAIL; i > RCU_DONE_TAIL; i--)
+		if (rsclp->tails[i] != rsclp->tails[i - 1] &&
+		    ULONG_CMP_LT(rsclp->gp_seq[i], seq))
+			break;
+
+	/*
+	 * If all the segments contain callbacks that correspond to
+	 * earlier grace-period sequence numbers than "seq", leave.
+	 * Assuming that the rcu_segcblist structure has enough
+	 * segments in its arrays, this can only happen if some of
+	 * the non-done segments contain callbacks that really are
+	 * ready to invoke.  This situation will get straightened
+	 * out by the next call to rcu_segcblist_advance().
+	 *
+	 * Also advance to the oldest segment of callbacks whose
+	 * ->gp_seq[] completion is at or after that passed in via "seq",
+	 * skipping any empty segments.
+	 */
+	if (++i >= RCU_NEXT_TAIL)
+		return false;
+
+	/*
+	 * Merge all later callbacks, including newly arrived callbacks,
+	 * into the segment located by the for-loop above.  Assign "seq"
+	 * as the ->gp_seq[] value in order to correctly handle the case
+	 * where there were no pending callbacks in the rcu_segcblist
+	 * structure other than in the RCU_NEXT_TAIL segment.
+	 */
+	for (; i < RCU_NEXT_TAIL; i++) {
+		rsclp->tails[i] = rsclp->tails[RCU_NEXT_TAIL];
+		rsclp->gp_seq[i] = seq;
+	}
+	return true;
+}
+
+/*
+ * Scan the specified rcu_segcblist structure for callbacks that need
+ * a grace period later than the one specified by "seq".  We don't look
+ * at the RCU_DONE_TAIL or RCU_NEXT_TAIL segments because they don't
+ * have a grace-period sequence number.
+ */
+static inline bool rcu_segcblist_future_gp_needed(struct rcu_segcblist *rsclp,
+						  unsigned long seq)
+{
+	int i;
+
+	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
+		if (rsclp->tails[i - 1] != rsclp->tails[i] &&
+		    ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
+		    	return true;
+	return false;
+}
+
+/*
+ * Interim function to return rcu_segcblist head pointer.  Longer term, the
+ * rcu_segcblist will be used more pervasively, removing the need for this
+ * function.
+ */
+static inline struct rcu_head *rcu_segcblist_head(struct rcu_segcblist *rsclp)
+{
+	return rsclp->head;
+}
+
+/*
+ * Interim function to return rcu_segcblist head pointer.  Longer term, the
+ * rcu_segcblist will be used more pervasively, removing the need for this
+ * function.
+ */
+static inline struct rcu_head **rcu_segcblist_tail(struct rcu_segcblist *rsclp)
+{
+	WARN_ON_ONCE(rcu_segcblist_empty(rsclp));
+	return rsclp->tails[RCU_NEXT_TAIL];
+}
+
+#endif /* __KERNEL_RCU_SEGCBLIST_H */
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index ef4b8f63c06d..00390965c843 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -97,8 +97,8 @@ struct rcu_state sname##_state = { \
 	.gpnum = 0UL - 300UL, \
 	.completed = 0UL - 300UL, \
 	.orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
-	.orphan_nxttail = &sname##_state.orphan_nxtlist, \
-	.orphan_donetail = &sname##_state.orphan_donelist, \
+	.orphan_pend = RCU_CBLIST_INITIALIZER(sname##_state.orphan_pend), \
+	.orphan_done = RCU_CBLIST_INITIALIZER(sname##_state.orphan_done), \
 	.barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
 	.name = RCU_STATE_NAME(sname), \
 	.abbr = sabbr, \
@@ -733,16 +733,6 @@ void rcutorture_record_progress(unsigned long vernum)
 EXPORT_SYMBOL_GPL(rcutorture_record_progress);
 
 /*
- * Does the CPU have callbacks ready to be invoked?
- */
-static int
-cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
-{
-	return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] &&
-	       rdp->nxttail[RCU_NEXT_TAIL] != NULL;
-}
-
-/*
  * Return the root node of the specified rcu_state structure.
  */
 static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
@@ -772,21 +762,17 @@ static int rcu_future_needs_gp(struct rcu_state *rsp)
 static bool
 cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
 {
-	int i;
-
 	if (rcu_gp_in_progress(rsp))
 		return false;  /* No, a grace period is already in progress. */
 	if (rcu_future_needs_gp(rsp))
 		return true;  /* Yes, a no-CBs CPU needs one. */
-	if (!rdp->nxttail[RCU_NEXT_TAIL])
+	if (!rcu_segcblist_is_enabled(&rdp->cblist))
 		return false;  /* No, this is a no-CBs (or offline) CPU. */
-	if (*rdp->nxttail[RCU_NEXT_READY_TAIL])
+	if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
 		return true;  /* Yes, CPU has newly registered callbacks. */
-	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
-		if (rdp->nxttail[i - 1] != rdp->nxttail[i] &&
-		    ULONG_CMP_LT(READ_ONCE(rsp->completed),
-				 rdp->nxtcompleted[i]))
-			return true;  /* Yes, CBs for future grace period. */
+	if (rcu_segcblist_future_gp_needed(&rdp->cblist,
+					   READ_ONCE(rsp->completed)))
+		return true;  /* Yes, CBs for future grace period. */
 	return false; /* No grace period needed. */
 }
 
@@ -1497,7 +1483,8 @@ static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
 
 	print_cpu_stall_info_end();
 	for_each_possible_cpu(cpu)
-		totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
+		totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
+							    cpu)->cblist);
 	pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n",
 	       smp_processor_id(), (long)(jiffies - rsp->gp_start),
 	       (long)rsp->gpnum, (long)rsp->completed, totqlen);
@@ -1551,7 +1538,8 @@ static void print_cpu_stall(struct rcu_state *rsp)
 	print_cpu_stall_info(rsp, smp_processor_id());
 	print_cpu_stall_info_end();
 	for_each_possible_cpu(cpu)
-		totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
+		totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
+							    cpu)->cblist);
 	pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
 		jiffies - rsp->gp_start,
 		(long)rsp->gpnum, (long)rsp->completed, totqlen);
@@ -1654,30 +1642,6 @@ void rcu_cpu_stall_reset(void)
 }
 
 /*
- * Initialize the specified rcu_data structure's default callback list
- * to empty.  The default callback list is the one that is not used by
- * no-callbacks CPUs.
- */
-static void init_default_callback_list(struct rcu_data *rdp)
-{
-	int i;
-
-	rdp->nxtlist = NULL;
-	for (i = 0; i < RCU_NEXT_SIZE; i++)
-		rdp->nxttail[i] = &rdp->nxtlist;
-}
-
-/*
- * Initialize the specified rcu_data structure's callback list to empty.
- */
-static void init_callback_list(struct rcu_data *rdp)
-{
-	if (init_nocb_callback_list(rdp))
-		return;
-	init_default_callback_list(rdp);
-}
-
-/*
  * Determine the value that ->completed will have at the end of the
  * next subsequent grace period.  This is used to tag callbacks so that
  * a CPU can invoke callbacks in a timely fashion even if that CPU has
@@ -1731,7 +1695,6 @@ rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
 		    unsigned long *c_out)
 {
 	unsigned long c;
-	int i;
 	bool ret = false;
 	struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
 
@@ -1777,13 +1740,11 @@ rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
 	/*
 	 * Get a new grace-period number.  If there really is no grace
 	 * period in progress, it will be smaller than the one we obtained
-	 * earlier.  Adjust callbacks as needed.  Note that even no-CBs
-	 * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed.
+	 * earlier.  Adjust callbacks as needed.
 	 */
 	c = rcu_cbs_completed(rdp->rsp, rnp_root);
-	for (i = RCU_DONE_TAIL; i < RCU_NEXT_TAIL; i++)
-		if (ULONG_CMP_LT(c, rdp->nxtcompleted[i]))
-			rdp->nxtcompleted[i] = c;
+	if (!rcu_is_nocb_cpu(rdp->cpu))
+		(void)rcu_segcblist_accelerate(&rdp->cblist, c);
 
 	/*
 	 * If the needed for the required grace period is already
@@ -1863,57 +1824,27 @@ static void rcu_gp_kthread_wake(struct rcu_state *rsp)
 static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
 			       struct rcu_data *rdp)
 {
-	unsigned long c;
-	int i;
-	bool ret;
-
-	/* If the CPU has no callbacks, nothing to do. */
-	if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
-		return false;
-
-	/*
-	 * Starting from the sublist containing the callbacks most
-	 * recently assigned a ->completed number and working down, find the
-	 * first sublist that is not assignable to an upcoming grace period.
-	 * Such a sublist has something in it (first two tests) and has
-	 * a ->completed number assigned that will complete sooner than
-	 * the ->completed number for newly arrived callbacks (last test).
-	 *
-	 * The key point is that any later sublist can be assigned the
-	 * same ->completed number as the newly arrived callbacks, which
-	 * means that the callbacks in any of these later sublist can be
-	 * grouped into a single sublist, whether or not they have already
-	 * been assigned a ->completed number.
-	 */
-	c = rcu_cbs_completed(rsp, rnp);
-	for (i = RCU_NEXT_TAIL - 1; i > RCU_DONE_TAIL; i--)
-		if (rdp->nxttail[i] != rdp->nxttail[i - 1] &&
-		    !ULONG_CMP_GE(rdp->nxtcompleted[i], c))
-			break;
+	bool ret = false;
 
-	/*
-	 * If there are no sublist for unassigned callbacks, leave.
-	 * At the same time, advance "i" one sublist, so that "i" will
-	 * index into the sublist where all the remaining callbacks should
-	 * be grouped into.
-	 */
-	if (++i >= RCU_NEXT_TAIL)
+	/* If no pending (not yet ready to invoke) callbacks, nothing to do. */
+	if (!rcu_segcblist_pend_cbs(&rdp->cblist))
 		return false;
 
 	/*
-	 * Assign all subsequent callbacks' ->completed number to the next
-	 * full grace period and group them all in the sublist initially
-	 * indexed by "i".
+	 * Callbacks are often registered with incomplete grace-period
+	 * information.  Something about the fact that getting exact
+	 * information requires acquiring a global lock...  RCU therefore
+	 * makes a conservative estimate of the grace period number at which
+	 * a given callback will become ready to invoke.	The following
+	 * code checks this estimate and improves it when possible, thus
+	 * accelerating callback invocation to an earlier grace-period
+	 * number.
 	 */
-	for (; i <= RCU_NEXT_TAIL; i++) {
-		rdp->nxttail[i] = rdp->nxttail[RCU_NEXT_TAIL];
-		rdp->nxtcompleted[i] = c;
-	}
-	/* Record any needed additional grace periods. */
-	ret = rcu_start_future_gp(rnp, rdp, NULL);
+	if (rcu_segcblist_accelerate(&rdp->cblist, rcu_cbs_completed(rsp, rnp)))
+		ret = rcu_start_future_gp(rnp, rdp, NULL);
 
 	/* Trace depending on how much we were able to accelerate. */
-	if (!*rdp->nxttail[RCU_WAIT_TAIL])
+	if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
 		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB"));
 	else
 		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB"));
@@ -1933,32 +1864,15 @@ static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
 static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
 			    struct rcu_data *rdp)
 {
-	int i, j;
-
-	/* If the CPU has no callbacks, nothing to do. */
-	if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
+	/* If no pending (not yet ready to invoke) callbacks, nothing to do. */
+	if (!rcu_segcblist_pend_cbs(&rdp->cblist))
 		return false;
 
 	/*
 	 * Find all callbacks whose ->completed numbers indicate that they
 	 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
 	 */
-	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
-		if (ULONG_CMP_LT(rnp->completed, rdp->nxtcompleted[i]))
-			break;
-		rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[i];
-	}
-	/* Clean up any sublist tail pointers that were misordered above. */
-	for (j = RCU_WAIT_TAIL; j < i; j++)
-		rdp->nxttail[j] = rdp->nxttail[RCU_DONE_TAIL];
-
-	/* Copy down callbacks to fill in empty sublists. */
-	for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
-		if (rdp->nxttail[j] == rdp->nxttail[RCU_NEXT_TAIL])
-			break;
-		rdp->nxttail[j] = rdp->nxttail[i];
-		rdp->nxtcompleted[j] = rdp->nxtcompleted[i];
-	}
+	rcu_segcblist_advance(&rdp->cblist, rnp->completed);
 
 	/* Classify any remaining callbacks. */
 	return rcu_accelerate_cbs(rsp, rnp, rdp);
@@ -2675,13 +2589,8 @@ rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
 	 * because _rcu_barrier() excludes CPU-hotplug operations, so it
 	 * cannot be running now.  Thus no memory barrier is required.
 	 */
-	if (rdp->nxtlist != NULL) {
-		rsp->qlen_lazy += rdp->qlen_lazy;
-		rsp->qlen += rdp->qlen;
-		rdp->n_cbs_orphaned += rdp->qlen;
-		rdp->qlen_lazy = 0;
-		WRITE_ONCE(rdp->qlen, 0);
-	}
+	rdp->n_cbs_orphaned += rcu_segcblist_n_cbs(&rdp->cblist);
+	rcu_segcblist_extract_count(&rdp->cblist, &rsp->orphan_done);
 
 	/*
 	 * Next, move those callbacks still needing a grace period to
@@ -2689,31 +2598,18 @@ rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
 	 * Some of the callbacks might have gone partway through a grace
 	 * period, but that is too bad.  They get to start over because we
 	 * cannot assume that grace periods are synchronized across CPUs.
-	 * We don't bother updating the ->nxttail[] array yet, instead
-	 * we just reset the whole thing later on.
 	 */
-	if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) {
-		*rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL];
-		rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL];
-		*rdp->nxttail[RCU_DONE_TAIL] = NULL;
-	}
+	rcu_segcblist_extract_pend_cbs(&rdp->cblist, &rsp->orphan_pend);
 
 	/*
 	 * Then move the ready-to-invoke callbacks to the orphanage,
 	 * where some other CPU will pick them up.  These will not be
 	 * required to pass though another grace period: They are done.
 	 */
-	if (rdp->nxtlist != NULL) {
-		*rsp->orphan_donetail = rdp->nxtlist;
-		rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
-	}
+	rcu_segcblist_extract_done_cbs(&rdp->cblist, &rsp->orphan_done);
 
-	/*
-	 * Finally, initialize the rcu_data structure's list to empty and
-	 * disallow further callbacks on this CPU.
-	 */
-	init_callback_list(rdp);
-	rdp->nxttail[RCU_NEXT_TAIL] = NULL;
+	/* Finally, disallow further callbacks on this CPU.  */
+	rcu_segcblist_disable(&rdp->cblist);
 }
 
 /*
@@ -2722,7 +2618,6 @@ rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
  */
 static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
 {
-	int i;
 	struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
 
 	/* No-CBs CPUs are handled specially. */
@@ -2731,13 +2626,11 @@ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
 		return;
 
 	/* Do the accounting first. */
-	rdp->qlen_lazy += rsp->qlen_lazy;
-	rdp->qlen += rsp->qlen;
-	rdp->n_cbs_adopted += rsp->qlen;
-	if (rsp->qlen_lazy != rsp->qlen)
+	rdp->n_cbs_adopted += rcu_cblist_n_cbs(&rsp->orphan_done);
+	if (rcu_cblist_n_lazy_cbs(&rsp->orphan_done) !=
+	    rcu_cblist_n_cbs(&rsp->orphan_done))
 		rcu_idle_count_callbacks_posted();
-	rsp->qlen_lazy = 0;
-	rsp->qlen = 0;
+	rcu_segcblist_insert_count(&rdp->cblist, &rsp->orphan_done);
 
 	/*
 	 * We do not need a memory barrier here because the only way we
@@ -2745,24 +2638,13 @@ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
 	 * we are the task doing the rcu_barrier().
 	 */
 
-	/* First adopt the ready-to-invoke callbacks. */
-	if (rsp->orphan_donelist != NULL) {
-		*rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL];
-		*rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist;
-		for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--)
-			if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
-				rdp->nxttail[i] = rsp->orphan_donetail;
-		rsp->orphan_donelist = NULL;
-		rsp->orphan_donetail = &rsp->orphan_donelist;
-	}
-
-	/* And then adopt the callbacks that still need a grace period. */
-	if (rsp->orphan_nxtlist != NULL) {
-		*rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist;
-		rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail;
-		rsp->orphan_nxtlist = NULL;
-		rsp->orphan_nxttail = &rsp->orphan_nxtlist;
-	}
+	/* First adopt the ready-to-invoke callbacks, then the done ones. */
+	rcu_segcblist_insert_done_cbs(&rdp->cblist, &rsp->orphan_done);
+	WARN_ON_ONCE(!rcu_cblist_empty(&rsp->orphan_done));
+	rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rsp->orphan_pend);
+	WARN_ON_ONCE(!rcu_cblist_empty(&rsp->orphan_pend));
+	WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) !=
+		     !rcu_segcblist_n_cbs(&rdp->cblist));
 }
 
 /*
@@ -2850,9 +2732,11 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
 	rcu_adopt_orphan_cbs(rsp, flags);
 	raw_spin_unlock_irqrestore(&rsp->orphan_lock, flags);
 
-	WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
-		  "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
-		  cpu, rdp->qlen, rdp->nxtlist);
+	WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
+		  !rcu_segcblist_empty(&rdp->cblist),
+		  "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
+		  cpu, rcu_segcblist_n_cbs(&rdp->cblist),
+		  rcu_segcblist_first_cb(&rdp->cblist));
 }
 
 /*
@@ -2862,14 +2746,17 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
 static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
 {
 	unsigned long flags;
-	struct rcu_head *next, *list, **tail;
-	long bl, count, count_lazy;
-	int i;
+	struct rcu_head *rhp;
+	struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
+	long bl, count;
 
 	/* If no callbacks are ready, just return. */
-	if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
-		trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
-		trace_rcu_batch_end(rsp->name, 0, !!READ_ONCE(rdp->nxtlist),
+	if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
+		trace_rcu_batch_start(rsp->name,
+				      rcu_segcblist_n_lazy_cbs(&rdp->cblist),
+				      rcu_segcblist_n_cbs(&rdp->cblist), 0);
+		trace_rcu_batch_end(rsp->name, 0,
+				    !rcu_segcblist_empty(&rdp->cblist),
 				    need_resched(), is_idle_task(current),
 				    rcu_is_callbacks_kthread());
 		return;
@@ -2877,73 +2764,62 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
 
 	/*
 	 * Extract the list of ready callbacks, disabling to prevent
-	 * races with call_rcu() from interrupt handlers.
+	 * races with call_rcu() from interrupt handlers.  Leave the
+	 * callback counts, as rcu_barrier() needs to be conservative.
 	 */
 	local_irq_save(flags);
 	WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
 	bl = rdp->blimit;
-	trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
-	list = rdp->nxtlist;
-	rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
-	*rdp->nxttail[RCU_DONE_TAIL] = NULL;
-	tail = rdp->nxttail[RCU_DONE_TAIL];
-	for (i = RCU_NEXT_SIZE - 1; i >= 0; i--)
-		if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
-			rdp->nxttail[i] = &rdp->nxtlist;
+	trace_rcu_batch_start(rsp->name, rcu_segcblist_n_lazy_cbs(&rdp->cblist),
+			      rcu_segcblist_n_cbs(&rdp->cblist), bl);
+	rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
 	local_irq_restore(flags);
 
 	/* Invoke callbacks. */
-	count = count_lazy = 0;
-	while (list) {
-		next = list->next;
-		prefetch(next);
-		debug_rcu_head_unqueue(list);
-		if (__rcu_reclaim(rsp->name, list))
-			count_lazy++;
-		list = next;
-		/* Stop only if limit reached and CPU has something to do. */
-		if (++count >= bl &&
+	rhp = rcu_cblist_dequeue(&rcl);
+	for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
+		debug_rcu_head_unqueue(rhp);
+		if (__rcu_reclaim(rsp->name, rhp))
+			rcu_cblist_dequeued_lazy(&rcl);
+		/*
+		 * Stop only if limit reached and CPU has something to do.
+		 * Note: The rcl structure counts down from zero.
+		 */
+		if (-rcu_cblist_n_cbs(&rcl) >= bl &&
 		    (need_resched() ||
 		     (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
 			break;
 	}
 
 	local_irq_save(flags);
-	trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
-			    is_idle_task(current),
+	count = -rcu_cblist_n_cbs(&rcl);
+	trace_rcu_batch_end(rsp->name, count, !rcu_cblist_empty(&rcl),
+			    need_resched(), is_idle_task(current),
 			    rcu_is_callbacks_kthread());
 
-	/* Update count, and requeue any remaining callbacks. */
-	if (list != NULL) {
-		*tail = rdp->nxtlist;
-		rdp->nxtlist = list;
-		for (i = 0; i < RCU_NEXT_SIZE; i++)
-			if (&rdp->nxtlist == rdp->nxttail[i])
-				rdp->nxttail[i] = tail;
-			else
-				break;
-	}
+	/* Update counts and requeue any remaining callbacks. */
+	rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
 	smp_mb(); /* List handling before counting for rcu_barrier(). */
-	rdp->qlen_lazy -= count_lazy;
-	WRITE_ONCE(rdp->qlen, rdp->qlen - count);
 	rdp->n_cbs_invoked += count;
+	rcu_segcblist_insert_count(&rdp->cblist, &rcl);
 
 	/* Reinstate batch limit if we have worked down the excess. */
-	if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
+	count = rcu_segcblist_n_cbs(&rdp->cblist);
+	if (rdp->blimit == LONG_MAX && count <= qlowmark)
 		rdp->blimit = blimit;
 
 	/* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
-	if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
+	if (count == 0 && rdp->qlen_last_fqs_check != 0) {
 		rdp->qlen_last_fqs_check = 0;
 		rdp->n_force_qs_snap = rsp->n_force_qs;
-	} else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
-		rdp->qlen_last_fqs_check = rdp->qlen;
-	WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));
+	} else if (count < rdp->qlen_last_fqs_check - qhimark)
+		rdp->qlen_last_fqs_check = count;
+	WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) != (count == 0));
 
 	local_irq_restore(flags);
 
 	/* Re-invoke RCU core processing if there are callbacks remaining. */
-	if (cpu_has_callbacks_ready_to_invoke(rdp))
+	if (rcu_segcblist_ready_cbs(&rdp->cblist))
 		invoke_rcu_core();
 }
 
@@ -3127,7 +3003,7 @@ __rcu_process_callbacks(struct rcu_state *rsp)
 	}
 
 	/* If there are callbacks ready, invoke them. */
-	if (cpu_has_callbacks_ready_to_invoke(rdp))
+	if (rcu_segcblist_ready_cbs(&rdp->cblist))
 		invoke_rcu_callbacks(rsp, rdp);
 
 	/* Do any needed deferred wakeups of rcuo kthreads. */
@@ -3199,7 +3075,8 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
 	 * invoking force_quiescent_state() if the newly enqueued callback
 	 * is the only one waiting for a grace period to complete.
 	 */
-	if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
+	if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
+		     rdp->qlen_last_fqs_check + qhimark)) {
 
 		/* Are we ignoring a completed grace period? */
 		note_gp_changes(rsp, rdp);
@@ -3217,10 +3094,10 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
 			/* Give the grace period a kick. */
 			rdp->blimit = LONG_MAX;
 			if (rsp->n_force_qs == rdp->n_force_qs_snap &&
-			    *rdp->nxttail[RCU_DONE_TAIL] != head)
+			    rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
 				force_quiescent_state(rsp);
 			rdp->n_force_qs_snap = rsp->n_force_qs;
-			rdp->qlen_last_fqs_check = rdp->qlen;
+			rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
 		}
 	}
 }
@@ -3260,7 +3137,7 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func,
 	rdp = this_cpu_ptr(rsp->rda);
 
 	/* Add the callback to our list. */
-	if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL) || cpu != -1) {
+	if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist)) || cpu != -1) {
 		int offline;
 
 		if (cpu != -1)
@@ -3279,23 +3156,21 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func,
 		 */
 		BUG_ON(cpu != -1);
 		WARN_ON_ONCE(!rcu_is_watching());
-		if (!likely(rdp->nxtlist))
-			init_default_callback_list(rdp);
+		if (rcu_segcblist_empty(&rdp->cblist))
+			rcu_segcblist_init(&rdp->cblist);
 	}
-	WRITE_ONCE(rdp->qlen, rdp->qlen + 1);
-	if (lazy)
-		rdp->qlen_lazy++;
-	else
+	rcu_segcblist_enqueue(&rdp->cblist, head, lazy);
+	if (!lazy)
 		rcu_idle_count_callbacks_posted();
-	smp_mb();  /* Count before adding callback for rcu_barrier(). */
-	*rdp->nxttail[RCU_NEXT_TAIL] = head;
-	rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
 
 	if (__is_kfree_rcu_offset((unsigned long)func))
 		trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
-					 rdp->qlen_lazy, rdp->qlen);
+					 rcu_segcblist_n_lazy_cbs(&rdp->cblist),
+					 rcu_segcblist_n_cbs(&rdp->cblist));
 	else
-		trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
+		trace_rcu_callback(rsp->name, head,
+				   rcu_segcblist_n_lazy_cbs(&rdp->cblist),
+				   rcu_segcblist_n_cbs(&rdp->cblist));
 
 	/* Go handle any RCU core processing required. */
 	__call_rcu_core(rsp, rdp, head, flags);
@@ -3607,7 +3482,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
 	}
 
 	/* Does this CPU have callbacks ready to invoke? */
-	if (cpu_has_callbacks_ready_to_invoke(rdp)) {
+	if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
 		rdp->n_rp_cb_ready++;
 		return 1;
 	}
@@ -3671,10 +3546,10 @@ static bool __maybe_unused rcu_cpu_has_callbacks(bool *all_lazy)
 
 	for_each_rcu_flavor(rsp) {
 		rdp = this_cpu_ptr(rsp->rda);
-		if (!rdp->nxtlist)
+		if (rcu_segcblist_empty(&rdp->cblist))
 			continue;
 		hc = true;
-		if (rdp->qlen != rdp->qlen_lazy || !all_lazy) {
+		if (rcu_segcblist_n_nonlazy_cbs(&rdp->cblist) || !all_lazy) {
 			al = false;
 			break;
 		}
@@ -3783,7 +3658,7 @@ static void _rcu_barrier(struct rcu_state *rsp)
 				__call_rcu(&rdp->barrier_head,
 					   rcu_barrier_callback, rsp, cpu, 0);
 			}
-		} else if (READ_ONCE(rdp->qlen)) {
+		} else if (rcu_segcblist_n_cbs(&rdp->cblist)) {
 			_rcu_barrier_trace(rsp, "OnlineQ", cpu,
 					   rsp->barrier_sequence);
 			smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
@@ -3892,8 +3767,9 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
 	rdp->qlen_last_fqs_check = 0;
 	rdp->n_force_qs_snap = rsp->n_force_qs;
 	rdp->blimit = blimit;
-	if (!rdp->nxtlist)
-		init_callback_list(rdp);  /* Re-enable callbacks on this CPU. */
+	if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */
+	    !init_nocb_callback_list(rdp))
+		rcu_segcblist_init(&rdp->cblist);  /* Re-enable callbacks. */
 	rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
 	rcu_sysidle_init_percpu_data(rdp->dynticks);
 	rcu_dynticks_eqs_online();
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 376c01e539c7..93889ff21dbb 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -30,6 +30,7 @@
 #include <linux/seqlock.h>
 #include <linux/swait.h>
 #include <linux/stop_machine.h>
+#include "rcu_segcblist.h"
 
 /*
  * Define shape of hierarchy based on NR_CPUS, CONFIG_RCU_FANOUT, and
@@ -335,34 +336,9 @@ struct rcu_data {
 					/* period it is aware of. */
 
 	/* 2) batch handling */
-	/*
-	 * If nxtlist is not NULL, it is partitioned as follows.
-	 * Any of the partitions might be empty, in which case the
-	 * pointer to that partition will be equal to the pointer for
-	 * the following partition.  When the list is empty, all of
-	 * the nxttail elements point to the ->nxtlist pointer itself,
-	 * which in that case is NULL.
-	 *
-	 * [nxtlist, *nxttail[RCU_DONE_TAIL]):
-	 *	Entries that batch # <= ->completed
-	 *	The grace period for these entries has completed, and
-	 *	the other grace-period-completed entries may be moved
-	 *	here temporarily in rcu_process_callbacks().
-	 * [*nxttail[RCU_DONE_TAIL], *nxttail[RCU_WAIT_TAIL]):
-	 *	Entries that batch # <= ->completed - 1: waiting for current GP
-	 * [*nxttail[RCU_WAIT_TAIL], *nxttail[RCU_NEXT_READY_TAIL]):
-	 *	Entries known to have arrived before current GP ended
-	 * [*nxttail[RCU_NEXT_READY_TAIL], *nxttail[RCU_NEXT_TAIL]):
-	 *	Entries that might have arrived after current GP ended
-	 *	Note that the value of *nxttail[RCU_NEXT_TAIL] will
-	 *	always be NULL, as this is the end of the list.
-	 */
-	struct rcu_head *nxtlist;
-	struct rcu_head **nxttail[RCU_NEXT_SIZE];
-	unsigned long	nxtcompleted[RCU_NEXT_SIZE];
-					/* grace periods for sublists. */
-	long		qlen_lazy;	/* # of lazy queued callbacks */
-	long		qlen;		/* # of queued callbacks, incl lazy */
+	struct rcu_segcblist cblist;	/* Segmented callback list, with */
+					/* different callbacks waiting for */
+					/* different grace periods. */
 	long		qlen_last_fqs_check;
 					/* qlen at last check for QS forcing */
 	unsigned long	n_cbs_invoked;	/* count of RCU cbs invoked. */
@@ -500,14 +476,11 @@ struct rcu_state {
 
 	raw_spinlock_t orphan_lock ____cacheline_internodealigned_in_smp;
 						/* Protect following fields. */
-	struct rcu_head *orphan_nxtlist;	/* Orphaned callbacks that */
+	struct rcu_cblist orphan_pend;		/* Orphaned callbacks that */
 						/*  need a grace period. */
-	struct rcu_head **orphan_nxttail;	/* Tail of above. */
-	struct rcu_head *orphan_donelist;	/* Orphaned callbacks that */
+	struct rcu_cblist orphan_done;		/* Orphaned callbacks that */
 						/*  are ready to invoke. */
-	struct rcu_head **orphan_donetail;	/* Tail of above. */
-	long qlen_lazy;				/* Number of lazy callbacks. */
-	long qlen;				/* Total number of callbacks. */
+						/* (Contains counts.) */
 	/* End of fields guarded by orphan_lock. */
 
 	struct mutex barrier_mutex;		/* Guards barrier fields. */
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 4a9df7ea89a4..db0a03474ae7 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1350,10 +1350,10 @@ static bool __maybe_unused rcu_try_advance_all_cbs(void)
 		 */
 		if ((rdp->completed != rnp->completed ||
 		     unlikely(READ_ONCE(rdp->gpwrap))) &&
-		    rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
+		    rcu_segcblist_pend_cbs(&rdp->cblist))
 			note_gp_changes(rsp, rdp);
 
-		if (cpu_has_callbacks_ready_to_invoke(rdp))
+		if (rcu_segcblist_ready_cbs(&rdp->cblist))
 			cbs_ready = true;
 	}
 	return cbs_ready;
@@ -1461,7 +1461,7 @@ static void rcu_prepare_for_idle(void)
 	rdtp->last_accelerate = jiffies;
 	for_each_rcu_flavor(rsp) {
 		rdp = this_cpu_ptr(rsp->rda);
-		if (!*rdp->nxttail[RCU_DONE_TAIL])
+		if (rcu_segcblist_pend_cbs(&rdp->cblist))
 			continue;
 		rnp = rdp->mynode;
 		raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
@@ -1529,7 +1529,7 @@ static void rcu_oom_notify_cpu(void *unused)
 
 	for_each_rcu_flavor(rsp) {
 		rdp = raw_cpu_ptr(rsp->rda);
-		if (rdp->qlen_lazy != 0) {
+		if (rcu_segcblist_n_lazy_cbs(&rdp->cblist)) {
 			atomic_inc(&oom_callback_count);
 			rsp->call(&rdp->oom_head, rcu_oom_callback);
 		}
@@ -1937,30 +1937,26 @@ static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
 						     struct rcu_data *rdp,
 						     unsigned long flags)
 {
-	long ql = rsp->qlen;
-	long qll = rsp->qlen_lazy;
+	long ql = rcu_cblist_n_cbs(&rsp->orphan_done);
+	long qll = rcu_cblist_n_lazy_cbs(&rsp->orphan_done);
 
 	/* If this is not a no-CBs CPU, tell the caller to do it the old way. */
 	if (!rcu_is_nocb_cpu(smp_processor_id()))
 		return false;
-	rsp->qlen = 0;
-	rsp->qlen_lazy = 0;
 
 	/* First, enqueue the donelist, if any.  This preserves CB ordering. */
-	if (rsp->orphan_donelist != NULL) {
-		__call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
-					rsp->orphan_donetail, ql, qll, flags);
-		ql = qll = 0;
-		rsp->orphan_donelist = NULL;
-		rsp->orphan_donetail = &rsp->orphan_donelist;
+	if (!rcu_cblist_empty(&rsp->orphan_done)) {
+		__call_rcu_nocb_enqueue(rdp, rcu_cblist_head(&rsp->orphan_done),
+					rcu_cblist_tail(&rsp->orphan_done),
+					ql, qll, flags);
 	}
-	if (rsp->orphan_nxtlist != NULL) {
-		__call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
-					rsp->orphan_nxttail, ql, qll, flags);
-		ql = qll = 0;
-		rsp->orphan_nxtlist = NULL;
-		rsp->orphan_nxttail = &rsp->orphan_nxtlist;
+	if (!rcu_cblist_empty(&rsp->orphan_pend)) {
+		__call_rcu_nocb_enqueue(rdp, rcu_cblist_head(&rsp->orphan_pend),
+					rcu_cblist_tail(&rsp->orphan_pend),
+					ql, qll, flags);
 	}
+	rcu_cblist_init(&rsp->orphan_done);
+	rcu_cblist_init(&rsp->orphan_pend);
 	return true;
 }
 
@@ -2403,16 +2399,16 @@ static bool init_nocb_callback_list(struct rcu_data *rdp)
 		return false;
 
 	/* If there are early-boot callbacks, move them to nocb lists. */
-	if (rdp->nxtlist) {
-		rdp->nocb_head = rdp->nxtlist;
-		rdp->nocb_tail = rdp->nxttail[RCU_NEXT_TAIL];
-		atomic_long_set(&rdp->nocb_q_count, rdp->qlen);
-		atomic_long_set(&rdp->nocb_q_count_lazy, rdp->qlen_lazy);
-		rdp->nxtlist = NULL;
-		rdp->qlen = 0;
-		rdp->qlen_lazy = 0;
+	if (!rcu_segcblist_empty(&rdp->cblist)) {
+		rdp->nocb_head = rcu_segcblist_head(&rdp->cblist);
+		rdp->nocb_tail = rcu_segcblist_tail(&rdp->cblist);
+		atomic_long_set(&rdp->nocb_q_count,
+				rcu_segcblist_n_cbs(&rdp->cblist));
+		atomic_long_set(&rdp->nocb_q_count_lazy,
+				rcu_segcblist_n_lazy_cbs(&rdp->cblist));
+		rcu_segcblist_init(&rdp->cblist);
 	}
-	rdp->nxttail[RCU_NEXT_TAIL] = NULL;
+	rcu_segcblist_disable(&rdp->cblist);
 	return true;
 }
 
diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c
index 65b43be38e68..066c64071a7b 100644
--- a/kernel/rcu/tree_trace.c
+++ b/kernel/rcu/tree_trace.c
@@ -41,6 +41,7 @@
 #include <linux/mutex.h>
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>
+#include <linux/prefetch.h>
 
 #define RCU_TREE_NONCORE
 #include "tree.h"
@@ -128,17 +129,15 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
 		   rdp->dynticks_fqs);
 	seq_printf(m, " of=%lu", rdp->offline_fqs);
 	rcu_nocb_q_lengths(rdp, &ql, &qll);
-	qll += rdp->qlen_lazy;
-	ql += rdp->qlen;
+	qll += rcu_segcblist_n_lazy_cbs(&rdp->cblist);
+	ql += rcu_segcblist_n_cbs(&rdp->cblist);
 	seq_printf(m, " ql=%ld/%ld qs=%c%c%c%c",
 		   qll, ql,
-		   ".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
-			rdp->nxttail[RCU_NEXT_TAIL]],
-		   ".R"[rdp->nxttail[RCU_WAIT_TAIL] !=
-			rdp->nxttail[RCU_NEXT_READY_TAIL]],
-		   ".W"[rdp->nxttail[RCU_DONE_TAIL] !=
-			rdp->nxttail[RCU_WAIT_TAIL]],
-		   ".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]]);
+		   ".N"[!rcu_segcblist_segempty(&rdp->cblist, RCU_NEXT_TAIL)],
+		   ".R"[!rcu_segcblist_segempty(&rdp->cblist,
+						RCU_NEXT_READY_TAIL)],
+		   ".W"[!rcu_segcblist_segempty(&rdp->cblist, RCU_WAIT_TAIL)],
+		   ".D"[!rcu_segcblist_segempty(&rdp->cblist, RCU_DONE_TAIL)]);
 #ifdef CONFIG_RCU_BOOST
 	seq_printf(m, " kt=%d/%c ktl=%x",
 		   per_cpu(rcu_cpu_has_work, rdp->cpu),
@@ -276,7 +275,9 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
 	seq_printf(m, "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu oqlen=%ld/%ld\n",
 		   rsp->n_force_qs, rsp->n_force_qs_ngp,
 		   rsp->n_force_qs - rsp->n_force_qs_ngp,
-		   READ_ONCE(rsp->n_force_qs_lh), rsp->qlen_lazy, rsp->qlen);
+		   READ_ONCE(rsp->n_force_qs_lh),
+		   rcu_cblist_n_lazy_cbs(&rsp->orphan_done),
+		   rcu_cblist_n_cbs(&rsp->orphan_done));
 	for (rnp = &rsp->node[0]; rnp - &rsp->node[0] < rcu_num_nodes; rnp++) {
 		if (rnp->level != level) {
 			seq_puts(m, "\n");
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 17/40] srcu: Allow SRCU to access rcu_scheduler_active
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (15 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 16/40] srcu: Abstract multi-tail callback list handling Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 18/40] srcu: Allow early boot use of synchronize_srcu() Paul E. McKenney
                   ` (23 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This is primarily a code-movement commit in preparation for allowing
SRCU to handle early-boot SRCU grace periods.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcutiny.h  |  6 +++---
 kernel/rcu/tiny_plugin.h |  9 +++++----
 kernel/rcu/tree.c        |  2 +-
 kernel/rcu/tree_exp.h    | 12 -----------
 kernel/rcu/update.c      | 52 +++++++++++++++++++++++++++++++-----------------
 5 files changed, 43 insertions(+), 38 deletions(-)

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 6c9d941e3962..5219be250f00 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -217,14 +217,14 @@ static inline void exit_rcu(void)
 {
 }
 
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
+#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU)
 extern int rcu_scheduler_active __read_mostly;
 void rcu_scheduler_starting(void);
-#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+#else /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU) */
 static inline void rcu_scheduler_starting(void)
 {
 }
-#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+#endif /* #else #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU) */
 
 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE)
 
diff --git a/kernel/rcu/tiny_plugin.h b/kernel/rcu/tiny_plugin.h
index df3a60e19f07..371034e77f87 100644
--- a/kernel/rcu/tiny_plugin.h
+++ b/kernel/rcu/tiny_plugin.h
@@ -52,7 +52,7 @@ static struct rcu_ctrlblk rcu_bh_ctrlblk = {
 	RCU_TRACE(.name = "rcu_bh")
 };
 
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
+#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU)
 #include <linux/kernel_stat.h>
 
 int rcu_scheduler_active __read_mostly;
@@ -65,15 +65,16 @@ EXPORT_SYMBOL_GPL(rcu_scheduler_active);
  * to RCU_SCHEDULER_RUNNING, skipping the RCU_SCHEDULER_INIT stage.
  * The reason for this is that Tiny RCU does not need kthreads, so does
  * not have to care about the fact that the scheduler is half-initialized
- * at a certain phase of the boot process.
+ * at a certain phase of the boot process.  Unless SRCU is in the mix.
  */
 void __init rcu_scheduler_starting(void)
 {
 	WARN_ON(nr_context_switches() > 0);
-	rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
+	rcu_scheduler_active = IS_ENABLED(CONFIG_SRCU)
+		? RCU_SCHEDULER_INIT : RCU_SCHEDULER_RUNNING;
 }
 
-#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU) */
 
 #ifdef CONFIG_RCU_TRACE
 
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 00390965c843..5e827d636e0b 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3981,7 +3981,7 @@ early_initcall(rcu_spawn_gp_kthread);
  * task is booting the system, and such primitives are no-ops).  After this
  * function is called, any synchronous grace-period primitives are run as
  * expedited, with the requesting task driving the grace period forward.
- * A later core_initcall() rcu_exp_runtime_mode() will switch to full
+ * A later core_initcall() rcu_set_runtime_mode() will switch to full
  * runtime RCU functionality.
  */
 void rcu_scheduler_starting(void)
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index a1f52bbe9db6..51ca287828a2 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -737,15 +737,3 @@ void synchronize_rcu_expedited(void)
 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
 
 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
-
-/*
- * Switch to run-time mode once Tree RCU has fully initialized.
- */
-static int __init rcu_exp_runtime_mode(void)
-{
-	rcu_test_sync_prims();
-	rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
-	rcu_test_sync_prims();
-	return 0;
-}
-core_initcall(rcu_exp_runtime_mode);
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 55c8530316c7..c5df0d756900 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -124,7 +124,7 @@ EXPORT_SYMBOL(rcu_read_lock_sched_held);
  * non-expedited counterparts?  Intended for use within RCU.  Note
  * that if the user specifies both rcu_expedited and rcu_normal, then
  * rcu_normal wins.  (Except during the time period during boot from
- * when the first task is spawned until the rcu_exp_runtime_mode()
+ * when the first task is spawned until the rcu_set_runtime_mode()
  * core_initcall() is invoked, at which point everything is expedited.)
  */
 bool rcu_gp_is_normal(void)
@@ -190,6 +190,39 @@ void rcu_end_inkernel_boot(void)
 
 #endif /* #ifndef CONFIG_TINY_RCU */
 
+/*
+ * Test each non-SRCU synchronous grace-period wait API.  This is
+ * useful just after a change in mode for these primitives, and
+ * during early boot.
+ */
+void rcu_test_sync_prims(void)
+{
+	if (!IS_ENABLED(CONFIG_PROVE_RCU))
+		return;
+	synchronize_rcu();
+	synchronize_rcu_bh();
+	synchronize_sched();
+	synchronize_rcu_expedited();
+	synchronize_rcu_bh_expedited();
+	synchronize_sched_expedited();
+}
+
+#if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU)
+
+/*
+ * Switch to run-time mode once RCU has fully initialized.
+ */
+static int __init rcu_set_runtime_mode(void)
+{
+	rcu_test_sync_prims();
+	rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
+	rcu_test_sync_prims();
+	return 0;
+}
+core_initcall(rcu_set_runtime_mode);
+
+#endif /* #if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU) */
+
 #ifdef CONFIG_PREEMPT_RCU
 
 /*
@@ -817,23 +850,6 @@ static void rcu_spawn_tasks_kthread(void)
 
 #endif /* #ifdef CONFIG_TASKS_RCU */
 
-/*
- * Test each non-SRCU synchronous grace-period wait API.  This is
- * useful just after a change in mode for these primitives, and
- * during early boot.
- */
-void rcu_test_sync_prims(void)
-{
-	if (!IS_ENABLED(CONFIG_PROVE_RCU))
-		return;
-	synchronize_rcu();
-	synchronize_rcu_bh();
-	synchronize_sched();
-	synchronize_rcu_expedited();
-	synchronize_rcu_bh_expedited();
-	synchronize_sched_expedited();
-}
-
 #ifdef CONFIG_PROVE_RCU
 
 /*
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12
@ 2017-04-12 17:40 Paul E. McKenney
  2017-04-12 17:39 ` [PATCH tip/core/rcu 01/40] rcu: Maintain special bits at bottom of ->dynticks counter Paul E. McKenney
                   ` (40 more replies)
  0 siblings, 41 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani

Hello!

This series moves SRCU from its traditional single per-srcu_struct
callback queue to per-srcu_struct/per-CPU callback queues.  This involves
abstracting functionality from Tree RCU, which results in a large
conflict footprint, which in turn results in some otherwise unrelated
patches coming along for the ride.

1.	Maintain special bits at bottom of ->dynticks counter.
	This is for some upcoming MM work.  My intent was to hold
	it until that work was ready, but merge conflicts dictated
	otherwise.  If the MM work does not appear soonish, I will
	manually revert this patch.

2.	Make arch select smp_mb__after_unlock_lock() strength, which
	gets rid of an arch-specific #ifdef.

3.	Consolidate SRCU batch checking into rcu_all_batches_empty().

4.	Check for tardy grace-period activity in cleanup_srcu_struct().

5-7.	Semicolon inside RCU_TRACE() for various parts of RCU.

8-10.	Make various parts of RCU do deferred NOCB wakeups in order to
	prevent callback blockages, and thus hangs.

11.	Pull rcu_sched_qs_mask into rcu_dynticks structure in order to
	eliminate an isolated per-CPU variable.

12.	Pull rcu_qs_ctr into rcu_dynticks structure.

13.	Eliminate flavor scan in rcu_momentary_dyntick_idle() to
	reduce semi-common-case context-switch overhead.

14.	Place guard on rcu_all_qs() and rcu_note_context_switch()
	actions to reduce common-case scheduler-fastpath overhead.

15.	Default RCU_FANOUT_LEAF to 16 unless explicitly changed.

16.	Abstract multi-tail callback list handling for SRCU.

17.	Allow SRCU to access rcu_scheduler_active.

18.	Allow early boot use of synchronize_srcu(), though not yet
	mid-boot use.

19.	Add single-element dequeue functions to rcu_segcblist for
	debug use.

20.	Move rcu_seq_start() and friends to rcu.h for SRCU's benefit.

21.	Expedited wakeups need to be fully ordered.

22.	Fix warning in rcu_seq_end().

23.	Push srcu_advance_batches() fastpath into common case as a
	step towards callback parallelization.

24.	Move to state-based grace-period sequencing, also as a step
	towards callback parallelization.

25.	Add grace-period sequence numbers to SRCU.

26.	Use rcu_segcblist to track SRCU callbacks.

27.	Move combining-tree definitions for SRCU's benefit.

28.	Move rcu_init_levelspread() to rcu_tree_node.h for SRCU's benefit.

29.	Remove redundant levelcnt[] array from rcu_init_one().

30.	Move rcu_node traversal macros to rcu.h for SRCU's benefit.

31.	Make num_rcu_lvl[] array be external for SRCU's benefit.

32.	Fix bogus try_check_zero() comment.

33.	Improve rcu_seq grace-period-counter abstraction for SRCU's
	benefit.

34.	Allow a second bit in rcu_seq for SRCU state.

35.	Merge ->srcu_state into ->srcu_gp_seq to allow atomic updates.

36.	Provide crude control of expedited SRCU grace periods.

37.	Create a tiny SRCU for bloatwatch/tinification.

38.	Print Tiny SRCU reader statistics in rcutorture.

39.	Introduce CLASSIC_SRCU Kconfig option for those who do not
	wish to help debug Tree SRCU.

40.	Parallelize SRCU callback handling.

							Thanx, Paul

------------------------------------------------------------------------

 /kernel/rcu/rcu_segcblist.h                                     |  671 -----
 b/Documentation/RCU/Design/Data-Structures/Data-Structures.html |   36 
 b/arch/Kconfig                                                  |    3 
 b/arch/powerpc/Kconfig                                          |    1 
 b/include/linux/rcu_node_tree.h                                 |  105 
 b/include/linux/rcu_segcblist.h                                 |  720 +++++
 b/include/linux/rcupdate.h                                      |    6 
 b/include/linux/rcutiny.h                                       |   11 
 b/include/linux/srcu.h                                          |  112 
 b/include/linux/srcuclassic.h                                   |  101 
 b/include/linux/srcutiny.h                                      |   81 
 b/include/linux/srcutree.h                                      |  171 +
 b/init/Kconfig                                                  |   33 
 b/kernel/rcu/Makefile                                           |    6 
 b/kernel/rcu/rcu.h                                              |  165 +
 b/kernel/rcu/rcu_segcblist.h                                    |  671 +++++
 b/kernel/rcu/rcutorture.c                                       |   39 
 b/kernel/rcu/srcu.c                                             |  846 +++---
 b/kernel/rcu/srcutiny.c                                         |  215 +
 b/kernel/rcu/srcutree.c                                         | 1252 ++++++++--
 b/kernel/rcu/tiny.c                                             |   20 
 b/kernel/rcu/tiny_plugin.h                                      |   13 
 b/kernel/rcu/tree.c                                             |  650 +----
 b/kernel/rcu/tree.h                                             |  174 -
 b/kernel/rcu/tree_exp.h                                         |   25 
 b/kernel/rcu/tree_plugin.h                                      |   70 
 b/kernel/rcu/tree_trace.c                                       |   26 
 b/kernel/rcu/update.c                                           |   52 
 28 files changed, 4261 insertions(+), 2014 deletions(-)

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 18/40] srcu: Allow early boot use of synchronize_srcu()
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (16 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 17/40] srcu: Allow SRCU to access rcu_scheduler_active Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 19/40] rcu: Add single-element dequeue functions to rcu_segcblist Paul E. McKenney
                   ` (22 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit checks for pre-scheduler state, and if that early in the
boot process, synchronize_srcu() and friends are no-ops.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/srcu.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 6beeba7b0b67..1026ce24922f 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -411,6 +411,8 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 			 lock_is_held(&rcu_sched_lock_map),
 			 "Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");
 
+	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
+		return;
 	might_sleep();
 	init_completion(&rcu.completion);
 
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 19/40] rcu: Add single-element dequeue functions to rcu_segcblist
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (17 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 18/40] srcu: Allow early boot use of synchronize_srcu() Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 20/40] srcu: Move rcu_seq_start() and friends to rcu.h Paul E. McKenney
                   ` (21 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit adds single-element dequeue functions to rcu_segcblist.
These are less efficient than using the extract and insert functions,
but allow more precise debugging code.  These functions are thus
expected to be used only in debug builds, for example, CONFIG_PROVE_RCU.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcu_segcblist.h | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
index 55b20ab5f940..c32d13b368ac 100644
--- a/kernel/rcu/rcu_segcblist.h
+++ b/kernel/rcu/rcu_segcblist.h
@@ -290,6 +290,51 @@ static inline bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp)
 }
 
 /*
+ * Dequeue and return the first ready-to-invoke callback.  If there
+ * are no ready-to-invoke callbacks, return NULL.  Disables interrupts
+ * to avoid interference.  Does not protect from interference from other
+ * CPUs or tasks.
+ */
+static inline struct rcu_head *
+rcu_segcblist_dequeue(struct rcu_segcblist *rsclp)
+{
+	unsigned long flags;
+	int i;
+	struct rcu_head *rhp;
+
+	local_irq_save(flags);
+	if (!rcu_segcblist_ready_cbs(rsclp)) {
+		local_irq_restore(flags);
+		return NULL;
+	}
+	rhp = rsclp->head;
+	BUG_ON(!rhp);
+	rsclp->head = rhp->next;
+	for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++) {
+		if (rsclp->tails[i] != &rhp->next)
+			break;
+		rsclp->tails[i] = &rsclp->head;
+	}
+	smp_mb(); /* Dequeue before decrement for rcu_barrier(). */
+	WRITE_ONCE(rsclp->len, rsclp->len - 1);
+	local_irq_restore(flags);
+	return rhp;
+}
+
+/*
+ * Account for the fact that a previously dequeued callback turned out
+ * to be marked as lazy.
+ */
+static inline void rcu_segcblist_dequeued_lazy(struct rcu_segcblist *rsclp)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	rsclp->len_lazy--;
+	local_irq_restore(flags);
+}
+
+/*
  * Return a pointer to the first callback in the specified rcu_segcblist
  * structure.  This is useful for diagnostics.
  */
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 20/40] srcu: Move rcu_seq_start() and friends to rcu.h
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (18 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 19/40] rcu: Add single-element dequeue functions to rcu_segcblist Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 21/40] rcu: Expedited wakeups need to be fully ordered Paul E. McKenney
                   ` (20 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit moves rcu_seq_start(), rcu_seq_end(), rcu_seq_snap(),
and rcu_seq_done() from kernel/rcu/tree.c to kernel/rcu/rcu.h.
This will allow SRCU to use these functions, which in turn will
allow SRCU to move from a single global callback queue to a
per-CPU callback queue.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcu.h  | 40 ++++++++++++++++++++++++++++++++++++++++
 kernel/rcu/tree.c | 35 -----------------------------------
 2 files changed, 40 insertions(+), 35 deletions(-)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 8700a81daf56..91e0bf31f6ce 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -56,6 +56,46 @@
 #define DYNTICK_TASK_EXIT_IDLE	   (DYNTICK_TASK_NEST_VALUE + \
 				    DYNTICK_TASK_FLAG)
 
+
+/*
+ * Grace-period counter management.
+ */
+
+/* Adjust sequence number for start of update-side operation. */
+static inline void rcu_seq_start(unsigned long *sp)
+{
+	WRITE_ONCE(*sp, *sp + 1);
+	smp_mb(); /* Ensure update-side operation after counter increment. */
+	WARN_ON_ONCE(!(*sp & 0x1));
+}
+
+/* Adjust sequence number for end of update-side operation. */
+static inline void rcu_seq_end(unsigned long *sp)
+{
+	smp_mb(); /* Ensure update-side operation before counter increment. */
+	WRITE_ONCE(*sp, *sp + 1);
+	WARN_ON_ONCE(*sp & 0x1);
+}
+
+/* Take a snapshot of the update side's sequence number. */
+static inline unsigned long rcu_seq_snap(unsigned long *sp)
+{
+	unsigned long s;
+
+	s = (READ_ONCE(*sp) + 3) & ~0x1;
+	smp_mb(); /* Above access must not bleed into critical section. */
+	return s;
+}
+
+/*
+ * Given a snapshot from rcu_seq_snap(), determine whether or not a
+ * full update-side operation has occurred.
+ */
+static inline bool rcu_seq_done(unsigned long *sp, unsigned long s)
+{
+	return ULONG_CMP_GE(READ_ONCE(*sp), s);
+}
+
 /*
  * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally
  * by call_rcu() and rcu callback execution, and are therefore not part of the
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 5e827d636e0b..f8b100902e21 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3416,41 +3416,6 @@ void cond_synchronize_sched(unsigned long oldstate)
 }
 EXPORT_SYMBOL_GPL(cond_synchronize_sched);
 
-/* Adjust sequence number for start of update-side operation. */
-static void rcu_seq_start(unsigned long *sp)
-{
-	WRITE_ONCE(*sp, *sp + 1);
-	smp_mb(); /* Ensure update-side operation after counter increment. */
-	WARN_ON_ONCE(!(*sp & 0x1));
-}
-
-/* Adjust sequence number for end of update-side operation. */
-static void rcu_seq_end(unsigned long *sp)
-{
-	smp_mb(); /* Ensure update-side operation before counter increment. */
-	WRITE_ONCE(*sp, *sp + 1);
-	WARN_ON_ONCE(*sp & 0x1);
-}
-
-/* Take a snapshot of the update side's sequence number. */
-static unsigned long rcu_seq_snap(unsigned long *sp)
-{
-	unsigned long s;
-
-	s = (READ_ONCE(*sp) + 3) & ~0x1;
-	smp_mb(); /* Above access must not bleed into critical section. */
-	return s;
-}
-
-/*
- * Given a snapshot from rcu_seq_snap(), determine whether or not a
- * full update-side operation has occurred.
- */
-static bool rcu_seq_done(unsigned long *sp, unsigned long s)
-{
-	return ULONG_CMP_GE(READ_ONCE(*sp), s);
-}
-
 /*
  * Check to see if there is any immediate RCU-related work to be done
  * by the current CPU, for the specified type of RCU, returning 1 if so.
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 21/40] rcu: Expedited wakeups need to be fully ordered
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (19 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 20/40] srcu: Move rcu_seq_start() and friends to rcu.h Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 22/40] rcu: Fix warning in rcu_seq_end() Paul E. McKenney
                   ` (19 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

Expedited grace periods use workqueue handlers that wake up the requesters,
but there is no lock mediating this wakeup.  Therefore, memory barriers
are required to ensure that the handler's memory references are seen by
all to occur before synchronize_*_expedited() returns to its caller.
Possibly detected by syzkaller.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree_exp.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 51ca287828a2..027e123d93c7 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -533,6 +533,7 @@ static void rcu_exp_wait_wake(struct rcu_state *rsp, unsigned long s)
 				rnp->exp_seq_rq = s;
 			spin_unlock(&rnp->exp_lock);
 		}
+		smp_mb(); /* All above changes before wakeup. */
 		wake_up_all(&rnp->exp_wq[(rsp->expedited_sequence >> 1) & 0x3]);
 	}
 	trace_rcu_exp_grace_period(rsp->name, s, TPS("endwake"));
@@ -614,6 +615,7 @@ static void _synchronize_rcu_expedited(struct rcu_state *rsp,
 	wait_event(rnp->exp_wq[(s >> 1) & 0x3],
 		   sync_exp_work_done(rsp,
 				      &rdp->exp_workdone0, s));
+	smp_mb(); /* Workqueue actions happen before return. */
 
 	/* Let the next expedited grace period start. */
 	mutex_unlock(&rsp->exp_mutex);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 22/40] rcu: Fix warning in rcu_seq_end()
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (20 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 21/40] rcu: Expedited wakeups need to be fully ordered Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 23/40] srcu: Push srcu_advance_batches() fastpath into common case Paul E. McKenney
                   ` (18 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Dmitry Vyukov, syzkaller, Paul E. McKenney

From: Dmitry Vyukov <dvyukov@google.com>

The rcu_seq_end() function increments seq signifying completion
of a grace period, after that checks that the seq is even and wakes
_synchronize_rcu_expedited().  The _synchronize_rcu_expedited() function
uses wait_event() to wait for even seq.  The problem is that wait_event()
can return as soon as seq becomes even without waiting for the wakeup.
In such case the warning in rcu_seq_end() can falsely fire if the next
expedited grace period starts before the check.

Check that seq has good value before incrementing it.

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Cc: syzkaller@googlegroups.com
Cc: linux-kernel@vger.kernel.org
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: josh@joshtriplett.org
Cc: jiangshanlai@gmail.com
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

---

syzkaller-triggered warning:

WARNING: CPU: 0 PID: 4832 at kernel/rcu/tree.c:3533
rcu_seq_end+0x110/0x140 kernel/rcu/tree.c:3533
CPU: 0 PID: 4832 Comm: kworker/0:3 Not tainted 4.10.0+ #276
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Workqueue: events wait_rcu_exp_gp
Call Trace:
 __dump_stack lib/dump_stack.c:15 [inline]
 dump_stack+0x2ee/0x3ef lib/dump_stack.c:51
 panic+0x1fb/0x412 kernel/panic.c:179
 __warn+0x1c4/0x1e0 kernel/panic.c:540
 warn_slowpath_null+0x2c/0x40 kernel/panic.c:583
 rcu_seq_end+0x110/0x140 kernel/rcu/tree.c:3533
 rcu_exp_gp_seq_end kernel/rcu/tree_exp.h:36 [inline]
 rcu_exp_wait_wake+0x8a9/0x1330 kernel/rcu/tree_exp.h:517
 rcu_exp_sel_wait_wake kernel/rcu/tree_exp.h:559 [inline]
 wait_rcu_exp_gp+0x83/0xc0 kernel/rcu/tree_exp.h:570
 process_one_work+0xc06/0x1c20 kernel/workqueue.c:2096
 worker_thread+0x223/0x19c0 kernel/workqueue.c:2230
 kthread+0x326/0x3f0 kernel/kthread.c:227
 ret_from_fork+0x31/0x40 arch/x86/entry/entry_64.S:430
---
---
 kernel/rcu/rcu.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 91e0bf31f6ce..0bc1313c49e2 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -73,8 +73,8 @@ static inline void rcu_seq_start(unsigned long *sp)
 static inline void rcu_seq_end(unsigned long *sp)
 {
 	smp_mb(); /* Ensure update-side operation before counter increment. */
+	WARN_ON_ONCE(!(*sp & 0x1));
 	WRITE_ONCE(*sp, *sp + 1);
-	WARN_ON_ONCE(*sp & 0x1);
 }
 
 /* Take a snapshot of the update side's sequence number. */
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 23/40] srcu: Push srcu_advance_batches() fastpath into common case
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (21 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 22/40] rcu: Fix warning in rcu_seq_end() Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 24/40] srcu: Move to state-based grace-period sequencing Paul E. McKenney
                   ` (17 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit simplifies the SRCU state machine by pushing the
srcu_advance_batches() idle-SRCU fastpath into the common case.  This is
done by giving srcu_reschedule() a delay parameter, which is zero in
the call from srcu_advance_batches().

This commit is a step towards numbering callbacks in order to
efficiently handle per-CPU callback lists.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/srcu.c | 27 +++++++--------------------
 1 file changed, 7 insertions(+), 20 deletions(-)

diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 1026ce24922f..febf87deaccb 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -393,8 +393,7 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 }
 EXPORT_SYMBOL_GPL(call_srcu);
 
-static void srcu_advance_batches(struct srcu_struct *sp, int trycount);
-static void srcu_reschedule(struct srcu_struct *sp);
+static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay);
 
 /*
  * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
@@ -403,7 +402,6 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 {
 	struct rcu_synchronize rcu;
 	struct rcu_head *head = &rcu.head;
-	bool done = false;
 
 	RCU_LOCKDEP_WARN(lock_is_held(&sp->dep_map) ||
 			 lock_is_held(&rcu_bh_lock_map) ||
@@ -425,25 +423,15 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 		sp->running = true;
 		rcu_batch_queue(&sp->batch_check0, head);
 		spin_unlock_irq(&sp->queue_lock);
-
-		srcu_advance_batches(sp, trycount);
-		if (!rcu_batch_empty(&sp->batch_done)) {
-			BUG_ON(sp->batch_done.head != head);
-			rcu_batch_dequeue(&sp->batch_done);
-			done = true;
-		}
 		/* give the processing owner to work_struct */
-		srcu_reschedule(sp);
+		srcu_reschedule(sp, 0);
 	} else {
 		rcu_batch_queue(&sp->batch_queue, head);
 		spin_unlock_irq(&sp->queue_lock);
 	}
 
-	if (!done) {
-		wait_for_completion(&rcu.completion);
-		smp_mb(); /* Caller's later accesses after GP. */
-	}
-
+	wait_for_completion(&rcu.completion);
+	smp_mb(); /* Caller's later accesses after GP. */
 }
 
 /**
@@ -633,7 +621,7 @@ static void srcu_invoke_callbacks(struct srcu_struct *sp)
  * Finished one round of SRCU grace period.  Start another if there are
  * more SRCU callbacks queued, otherwise put SRCU into not-running state.
  */
-static void srcu_reschedule(struct srcu_struct *sp)
+static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
 {
 	bool pending = true;
 
@@ -647,8 +635,7 @@ static void srcu_reschedule(struct srcu_struct *sp)
 	}
 
 	if (pending)
-		queue_delayed_work(system_power_efficient_wq,
-				   &sp->work, SRCU_INTERVAL);
+		queue_delayed_work(system_power_efficient_wq, &sp->work, delay);
 }
 
 /*
@@ -663,6 +650,6 @@ void process_srcu(struct work_struct *work)
 	srcu_collect_new(sp);
 	srcu_advance_batches(sp, 1);
 	srcu_invoke_callbacks(sp);
-	srcu_reschedule(sp);
+	srcu_reschedule(sp, SRCU_INTERVAL);
 }
 EXPORT_SYMBOL_GPL(process_srcu);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 24/40] srcu: Move to state-based grace-period sequencing
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (22 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 23/40] srcu: Push srcu_advance_batches() fastpath into common case Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 25/40] srcu: Add grace-period sequence numbers Paul E. McKenney
                   ` (16 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The current SRCU grace-period processing might never reach the last
portion of srcu_advance_batches().  This is OK given the current
implementation, as the first portion, up to the try_check_zero()
following the srcu_flip() is sufficient to drive grace periods forward.
However, it has the unfortunate side-effect of making it impossible to
determine when a given grace period has ended, and it will be necessary
to efficiently trace ends of grace periods in order to efficiently handle
per-CPU SRCU callback lists.

This commit therefore adds states to the SRCU grace-period processing,
so that the end of a given SRCU grace period is marked by the transition
to the SRCU_STATE_DONE state.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/srcu.h |  10 ++++-
 kernel/rcu/srcu.c    | 111 ++++++++++++++++++++++++++++-----------------------
 2 files changed, 69 insertions(+), 52 deletions(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index a598cf3ac70c..f149a685896c 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -48,7 +48,7 @@ struct srcu_struct {
 	unsigned long completed;
 	struct srcu_array __percpu *per_cpu_ref;
 	spinlock_t queue_lock; /* protect ->batch_queue, ->running */
-	bool running;
+	int srcu_state;
 	/* callbacks just queued */
 	struct rcu_batch batch_queue;
 	/* callbacks try to do the first check_zero */
@@ -62,6 +62,12 @@ struct srcu_struct {
 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 };
 
+/* Values for -> state variable. */
+#define SRCU_STATE_IDLE		0
+#define SRCU_STATE_SCAN1	1
+#define SRCU_STATE_SCAN2	2
+#define SRCU_STATE_DONE		3
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
 int __init_srcu_struct(struct srcu_struct *sp, const char *name,
@@ -89,7 +95,7 @@ void process_srcu(struct work_struct *work);
 		.completed = -300,					\
 		.per_cpu_ref = &name##_srcu_array,			\
 		.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock),	\
-		.running = false,					\
+		.srcu_state = SRCU_STATE_IDLE,				\
 		.batch_queue = RCU_BATCH_INIT(name.batch_queue),	\
 		.batch_check0 = RCU_BATCH_INIT(name.batch_check0),	\
 		.batch_check1 = RCU_BATCH_INIT(name.batch_check1),	\
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index febf87deaccb..84da09c02971 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -111,7 +111,7 @@ static int init_srcu_struct_fields(struct srcu_struct *sp)
 {
 	sp->completed = 0;
 	spin_lock_init(&sp->queue_lock);
-	sp->running = false;
+	sp->srcu_state = SRCU_STATE_IDLE;
 	rcu_batch_init(&sp->batch_queue);
 	rcu_batch_init(&sp->batch_check0);
 	rcu_batch_init(&sp->batch_check1);
@@ -264,7 +264,7 @@ void cleanup_srcu_struct(struct srcu_struct *sp)
 	if (WARN_ON(!rcu_all_batches_empty(sp)))
 		return; /* Leakage unless caller handles error. */
 	flush_delayed_work(&sp->work);
-	if (WARN_ON(sp->running))
+	if (WARN_ON(READ_ONCE(sp->srcu_state) != SRCU_STATE_IDLE))
 		return; /* Caller forgot to stop doing call_srcu()? */
 	free_percpu(sp->per_cpu_ref);
 	sp->per_cpu_ref = NULL;
@@ -385,8 +385,8 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 	spin_lock_irqsave(&sp->queue_lock, flags);
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
 	rcu_batch_queue(&sp->batch_queue, head);
-	if (!sp->running) {
-		sp->running = true;
+	if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) {
+		WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
 		queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
 	}
 	spin_unlock_irqrestore(&sp->queue_lock, flags);
@@ -418,9 +418,9 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 	head->func = wakeme_after_rcu;
 	spin_lock_irq(&sp->queue_lock);
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
-	if (!sp->running) {
+	if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) {
 		/* steal the processing owner */
-		sp->running = true;
+		WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
 		rcu_batch_queue(&sp->batch_check0, head);
 		spin_unlock_irq(&sp->queue_lock);
 		/* give the processing owner to work_struct */
@@ -542,7 +542,9 @@ static void srcu_collect_new(struct srcu_struct *sp)
  */
 static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 {
-	int idx = 1 ^ (sp->completed & 1);
+	int idx;
+
+	WARN_ON_ONCE(sp->srcu_state == SRCU_STATE_IDLE);
 
 	/*
 	 * Because readers might be delayed for an extended period after
@@ -552,48 +554,56 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 	 * invoking a callback.
 	 */
 
-	if (rcu_batch_empty(&sp->batch_check0) &&
-	    rcu_batch_empty(&sp->batch_check1))
-		return; /* no callbacks need to be advanced */
-
-	if (!try_check_zero(sp, idx, trycount))
-		return; /* failed to advance, will try after SRCU_INTERVAL */
-
-	/*
-	 * The callbacks in ->batch_check1 have already done with their
-	 * first zero check and flip back when they were enqueued on
-	 * ->batch_check0 in a previous invocation of srcu_advance_batches().
-	 * (Presumably try_check_zero() returned false during that
-	 * invocation, leaving the callbacks stranded on ->batch_check1.)
-	 * They are therefore ready to invoke, so move them to ->batch_done.
-	 */
-	rcu_batch_move(&sp->batch_done, &sp->batch_check1);
-
-	if (rcu_batch_empty(&sp->batch_check0))
-		return; /* no callbacks need to be advanced */
-	srcu_flip(sp);
-
-	/*
-	 * The callbacks in ->batch_check0 just finished their
-	 * first check zero and flip, so move them to ->batch_check1
-	 * for future checking on the other idx.
-	 */
-	rcu_batch_move(&sp->batch_check1, &sp->batch_check0);
-
-	/*
-	 * SRCU read-side critical sections are normally short, so check
-	 * at least twice in quick succession after a flip.
-	 */
-	trycount = trycount < 2 ? 2 : trycount;
-	if (!try_check_zero(sp, idx^1, trycount))
-		return; /* failed to advance, will try after SRCU_INTERVAL */
+	if (sp->srcu_state == SRCU_STATE_DONE)
+		WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
+
+	if (sp->srcu_state == SRCU_STATE_SCAN1) {
+		idx = 1 ^ (sp->completed & 1);
+		if (!try_check_zero(sp, idx, trycount))
+			return; /* readers present, retry after SRCU_INTERVAL */
+
+		/*
+		 * The callbacks in ->batch_check1 have already done
+		 * with their first zero check and flip back when they were
+		 * enqueued on ->batch_check0 in a previous invocation of
+		 * srcu_advance_batches().  (Presumably try_check_zero()
+		 * returned false during that invocation, leaving the
+		 * callbacks stranded on ->batch_check1.) They are therefore
+		 * ready to invoke, so move them to ->batch_done.
+		 */
+		rcu_batch_move(&sp->batch_done, &sp->batch_check1);
+		srcu_flip(sp);
+
+		/*
+		 * The callbacks in ->batch_check0 just finished their
+		 * first check zero and flip, so move them to ->batch_check1
+		 * for future checking on the other idx.
+		 */
+		rcu_batch_move(&sp->batch_check1, &sp->batch_check0);
+
+		WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN2);
+	}
 
-	/*
-	 * The callbacks in ->batch_check1 have now waited for all
-	 * pre-existing readers using both idx values.  They are therefore
-	 * ready to invoke, so move them to ->batch_done.
-	 */
-	rcu_batch_move(&sp->batch_done, &sp->batch_check1);
+	if (sp->srcu_state == SRCU_STATE_SCAN2) {
+
+		/*
+		 * SRCU read-side critical sections are normally short,
+		 * so check at least twice in quick succession after a flip.
+		 */
+		idx = 1 ^ (sp->completed & 1);
+		trycount = trycount < 2 ? 2 : trycount;
+		if (!try_check_zero(sp, idx, trycount))
+			return; /* readers present, retry after SRCU_INTERVAL */
+
+		/*
+		 * The callbacks in ->batch_check1 have now waited for
+		 * all pre-existing readers using both idx values.  They are
+		 * therefore ready to invoke, so move them to ->batch_done.
+		 */
+		rcu_batch_move(&sp->batch_done, &sp->batch_check1);
+
+		WRITE_ONCE(sp->srcu_state, SRCU_STATE_DONE);
+	}
 }
 
 /*
@@ -627,8 +637,9 @@ static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
 
 	if (rcu_all_batches_empty(sp)) {
 		spin_lock_irq(&sp->queue_lock);
-		if (rcu_all_batches_empty(sp)) {
-			sp->running = false;
+		if (rcu_all_batches_empty(sp) &&
+		    READ_ONCE(sp->srcu_state) == SRCU_STATE_DONE) {
+			WRITE_ONCE(sp->srcu_state, SRCU_STATE_IDLE);
 			pending = false;
 		}
 		spin_unlock_irq(&sp->queue_lock);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 25/40] srcu: Add grace-period sequence numbers
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (23 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 24/40] srcu: Move to state-based grace-period sequencing Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 26/40] srcu: Use rcu_segcblist to track SRCU callbacks Paul E. McKenney
                   ` (15 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit adds grace-period sequence numbers, which will be used to
handle mid-boot grace periods and per-CPU callback lists.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/srcu.h |  1 +
 kernel/rcu/srcu.c    | 27 +++++++++++++++++++++++----
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index f149a685896c..047ac8c28a4e 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -46,6 +46,7 @@ struct rcu_batch {
 
 struct srcu_struct {
 	unsigned long completed;
+	unsigned long srcu_gp_seq;
 	struct srcu_array __percpu *per_cpu_ref;
 	spinlock_t queue_lock; /* protect ->batch_queue, ->running */
 	int srcu_state;
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 84da09c02971..ed7c3d082b9f 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -110,6 +110,7 @@ static inline void rcu_batch_move(struct rcu_batch *to, struct rcu_batch *from)
 static int init_srcu_struct_fields(struct srcu_struct *sp)
 {
 	sp->completed = 0;
+	sp->srcu_gp_seq = 0;
 	spin_lock_init(&sp->queue_lock);
 	sp->srcu_state = SRCU_STATE_IDLE;
 	rcu_batch_init(&sp->batch_queue);
@@ -313,6 +314,15 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
 #define SYNCHRONIZE_SRCU_EXP_TRYCOUNT	12
 
 /*
+ * Start an SRCU grace period.
+ */
+static void srcu_gp_start(struct srcu_struct *sp)
+{
+	WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
+	rcu_seq_start(&sp->srcu_gp_seq);
+}
+
+/*
  * @@@ Wait until all pre-existing readers complete.  Such readers
  * will have used the index specified by "idx".
  * the caller should ensures the ->completed is not changed while checking
@@ -349,6 +359,15 @@ static void srcu_flip(struct srcu_struct *sp)
 }
 
 /*
+ * End an SRCU grace period.
+ */
+static void srcu_gp_end(struct srcu_struct *sp)
+{
+	rcu_seq_end(&sp->srcu_gp_seq);
+	WRITE_ONCE(sp->srcu_state, SRCU_STATE_DONE);
+}
+
+/*
  * Enqueue an SRCU callback on the specified srcu_struct structure,
  * initiating grace-period processing if it is not already running.
  *
@@ -386,7 +405,7 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
 	rcu_batch_queue(&sp->batch_queue, head);
 	if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) {
-		WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
+		srcu_gp_start(sp);
 		queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
 	}
 	spin_unlock_irqrestore(&sp->queue_lock, flags);
@@ -420,7 +439,7 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
 	if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) {
 		/* steal the processing owner */
-		WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
+		srcu_gp_start(sp);
 		rcu_batch_queue(&sp->batch_check0, head);
 		spin_unlock_irq(&sp->queue_lock);
 		/* give the processing owner to work_struct */
@@ -555,7 +574,7 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 	 */
 
 	if (sp->srcu_state == SRCU_STATE_DONE)
-		WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
+		srcu_gp_start(sp);
 
 	if (sp->srcu_state == SRCU_STATE_SCAN1) {
 		idx = 1 ^ (sp->completed & 1);
@@ -602,7 +621,7 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 		 */
 		rcu_batch_move(&sp->batch_done, &sp->batch_check1);
 
-		WRITE_ONCE(sp->srcu_state, SRCU_STATE_DONE);
+		srcu_gp_end(sp);
 	}
 }
 
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 26/40] srcu: Use rcu_segcblist to track SRCU callbacks
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (24 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 25/40] srcu: Add grace-period sequence numbers Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 27/40] srcu: Move combining-tree definitions for SRCU's benefit Paul E. McKenney
                   ` (14 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit switches SRCU from custom-built callback queues to the new
rcu_segcblist structure.  This change associates grace-period sequence
numbers with groups of callbacks, which will be needed for efficient
processing of per-CPU callbacks.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcu_segcblist.h | 678 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/srcu.h          |  24 +-
 kernel/rcu/rcu.h              |   6 +
 kernel/rcu/rcu_segcblist.h    | 671 -----------------------------------------
 kernel/rcu/srcu.c             | 159 ++--------
 kernel/rcu/tree.h             |   2 +-
 6 files changed, 721 insertions(+), 819 deletions(-)
 create mode 100644 include/linux/rcu_segcblist.h
 delete mode 100644 kernel/rcu/rcu_segcblist.h

diff --git a/include/linux/rcu_segcblist.h b/include/linux/rcu_segcblist.h
new file mode 100644
index 000000000000..74b1e7243955
--- /dev/null
+++ b/include/linux/rcu_segcblist.h
@@ -0,0 +1,678 @@
+/*
+ * RCU segmented callback lists
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright IBM Corporation, 2017
+ *
+ * Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ */
+
+#ifndef __KERNEL_RCU_SEGCBLIST_H
+#define __KERNEL_RCU_SEGCBLIST_H
+
+/* Simple unsegmented callback lists. */
+struct rcu_cblist {
+	struct rcu_head *head;
+	struct rcu_head **tail;
+	long len;
+	long len_lazy;
+};
+
+#define RCU_CBLIST_INITIALIZER(n) { .head = NULL, .tail = &n.head }
+
+/* Initialize simple callback list. */
+static inline void rcu_cblist_init(struct rcu_cblist *rclp)
+{
+	rclp->head = NULL;
+	rclp->tail = &rclp->head;
+	rclp->len = 0;
+	rclp->len_lazy = 0;
+}
+
+/* Is simple callback list empty? */
+static inline bool rcu_cblist_empty(struct rcu_cblist *rclp)
+{
+	return !rclp->head;
+}
+
+/* Return number of callbacks in simple callback list. */
+static inline long rcu_cblist_n_cbs(struct rcu_cblist *rclp)
+{
+	return rclp->len;
+}
+
+/* Return number of lazy callbacks in simple callback list. */
+static inline long rcu_cblist_n_lazy_cbs(struct rcu_cblist *rclp)
+{
+	return rclp->len_lazy;
+}
+
+/*
+ * Debug function to actually count the number of callbacks.
+ * If the number exceeds the limit specified, return -1.
+ */
+static inline long rcu_cblist_count_cbs(struct rcu_cblist *rclp, long lim)
+{
+	int cnt = 0;
+	struct rcu_head **rhpp = &rclp->head;
+
+	for (;;) {
+		if (!*rhpp)
+			return cnt;
+		if (++cnt > lim)
+			return -1;
+		rhpp = &(*rhpp)->next;
+	}
+}
+
+/*
+ * Dequeue the oldest rcu_head structure from the specified callback
+ * list.  This function assumes that the callback is non-lazy, but
+ * the caller can later invoke rcu_cblist_dequeued_lazy() if it
+ * finds otherwise (and if it cares about laziness).  This allows
+ * different users to have different ways of determining laziness.
+ */
+static inline struct rcu_head *rcu_cblist_dequeue(struct rcu_cblist *rclp)
+{
+	struct rcu_head *rhp;
+
+	rhp = rclp->head;
+	if (!rhp)
+		return NULL;
+	rclp->len--;
+	rclp->head = rhp->next;
+	if (!rclp->head)
+		rclp->tail = &rclp->head;
+	return rhp;
+}
+
+/*
+ * Account for the fact that a previously dequeued callback turned out
+ * to be marked as lazy.
+ */
+static inline void rcu_cblist_dequeued_lazy(struct rcu_cblist *rclp)
+{
+	rclp->len_lazy--;
+}
+
+/*
+ * Interim function to return rcu_cblist head pointer.  Longer term, the
+ * rcu_cblist will be used more pervasively, removing the need for this
+ * function.
+ */
+static inline struct rcu_head *rcu_cblist_head(struct rcu_cblist *rclp)
+{
+	return rclp->head;
+}
+
+/*
+ * Interim function to return rcu_cblist head pointer.  Longer term, the
+ * rcu_cblist will be used more pervasively, removing the need for this
+ * function.
+ */
+static inline struct rcu_head **rcu_cblist_tail(struct rcu_cblist *rclp)
+{
+	WARN_ON_ONCE(rcu_cblist_empty(rclp));
+	return rclp->tail;
+}
+
+/* Complicated segmented callback lists.  ;-) */
+
+/*
+ * Index values for segments in rcu_segcblist structure.
+ *
+ * The segments are as follows:
+ *
+ * [head, *tails[RCU_DONE_TAIL]):
+ *	Callbacks whose grace period has elapsed, and thus can be invoked.
+ * [*tails[RCU_DONE_TAIL], *tails[RCU_WAIT_TAIL]):
+ *	Callbacks waiting for the current GP from the current CPU's viewpoint.
+ * [*tails[RCU_WAIT_TAIL], *tails[RCU_NEXT_READY_TAIL]):
+ *	Callbacks that arrived before the next GP started, again from
+ *	the current CPU's viewpoint.  These can be handled by the next GP.
+ * [*tails[RCU_NEXT_READY_TAIL], *tails[RCU_NEXT_TAIL]):
+ *	Callbacks that might have arrived after the next GP started.
+ *	There is some uncertainty as to when a given GP starts and
+ *	ends, but a CPU knows the exact times if it is the one starting
+ *	or ending the GP.  Other CPUs know that the previous GP ends
+ *	before the next one starts.
+ *
+ * Note that RCU_WAIT_TAIL cannot be empty unless RCU_NEXT_READY_TAIL is also
+ * empty.
+ *
+ * The ->gp_seq[] array contains the grace-period number at which the
+ * corresponding segment of callbacks will be ready to invoke.  A given
+ * element of this array is meaningful only when the corresponding segment
+ * is non-empty, and it is never valid for RCU_DONE_TAIL (whose callbacks
+ * are already ready to invoke) or for RCU_NEXT_TAIL (whose callbacks have
+ * not yet been assigned a grace-period number).
+ */
+#define RCU_DONE_TAIL		0	/* Also RCU_WAIT head. */
+#define RCU_WAIT_TAIL		1	/* Also RCU_NEXT_READY head. */
+#define RCU_NEXT_READY_TAIL	2	/* Also RCU_NEXT head. */
+#define RCU_NEXT_TAIL		3
+#define RCU_CBLIST_NSEGS	4
+
+struct rcu_segcblist {
+	struct rcu_head *head;
+	struct rcu_head **tails[RCU_CBLIST_NSEGS];
+	unsigned long gp_seq[RCU_CBLIST_NSEGS];
+	long len;
+	long len_lazy;
+};
+
+#define RCU_SEGCBLIST_INITIALIZER(n) \
+{ \
+	.head = NULL, \
+	.tails[RCU_DONE_TAIL] = &n.head, \
+	.tails[RCU_WAIT_TAIL] = &n.head, \
+	.tails[RCU_NEXT_READY_TAIL] = &n.head, \
+	.tails[RCU_NEXT_TAIL] = &n.head, \
+}
+
+/*
+ * Initialize an rcu_segcblist structure.
+ */
+static inline void rcu_segcblist_init(struct rcu_segcblist *rsclp)
+{
+	int i;
+
+	BUILD_BUG_ON(RCU_NEXT_TAIL + 1 != ARRAY_SIZE(rsclp->gp_seq));
+	BUILD_BUG_ON(ARRAY_SIZE(rsclp->tails) != ARRAY_SIZE(rsclp->gp_seq));
+	rsclp->head = NULL;
+	for (i = 0; i < RCU_CBLIST_NSEGS; i++)
+		rsclp->tails[i] = &rsclp->head;
+	rsclp->len = 0;
+	rsclp->len_lazy = 0;
+}
+
+/*
+ * Is the specified rcu_segcblist structure empty?
+ *
+ * But careful!  The fact that the ->head field is NULL does not
+ * necessarily imply that there are no callbacks associated with
+ * this structure.  When callbacks are being invoked, they are
+ * removed as a group.  If callback invocation must be preempted,
+ * the remaining callbacks will be added back to the list.  Either
+ * way, the counts are updated later.
+ *
+ * So it is often the case that rcu_segcblist_n_cbs() should be used
+ * instead.
+ */
+static inline bool rcu_segcblist_empty(struct rcu_segcblist *rsclp)
+{
+	return !rsclp->head;
+}
+
+/* Return number of callbacks in segmented callback list. */
+static inline long rcu_segcblist_n_cbs(struct rcu_segcblist *rsclp)
+{
+	return READ_ONCE(rsclp->len);
+}
+
+/* Return number of lazy callbacks in segmented callback list. */
+static inline long rcu_segcblist_n_lazy_cbs(struct rcu_segcblist *rsclp)
+{
+	return rsclp->len_lazy;
+}
+
+/* Return number of lazy callbacks in segmented callback list. */
+static inline long rcu_segcblist_n_nonlazy_cbs(struct rcu_segcblist *rsclp)
+{
+	return rsclp->len - rsclp->len_lazy;
+}
+
+/*
+ * Is the specified rcu_segcblist enabled, for example, not corresponding
+ * to an offline or callback-offloaded CPU?
+ */
+static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp)
+{
+	return !!rsclp->tails[RCU_NEXT_TAIL];
+}
+
+/*
+ * Disable the specified rcu_segcblist structure, so that callbacks can
+ * no longer be posted to it.  This structure must be empty.
+ */
+static inline void rcu_segcblist_disable(struct rcu_segcblist *rsclp)
+{
+	WARN_ON_ONCE(!rcu_segcblist_empty(rsclp));
+	WARN_ON_ONCE(rcu_segcblist_n_cbs(rsclp));
+	WARN_ON_ONCE(rcu_segcblist_n_lazy_cbs(rsclp));
+	rsclp->tails[RCU_NEXT_TAIL] = NULL;
+}
+
+/*
+ * Is the specified segment of the specified rcu_segcblist structure
+ * empty of callbacks?
+ */
+static inline bool rcu_segcblist_segempty(struct rcu_segcblist *rsclp, int seg)
+{
+	if (seg == RCU_DONE_TAIL)
+		return &rsclp->head == rsclp->tails[RCU_DONE_TAIL];
+	return rsclp->tails[seg - 1] == rsclp->tails[seg];
+}
+
+/*
+ * Are all segments following the specified segment of the specified
+ * rcu_segcblist structure empty of callbacks?  (The specified
+ * segment might well contain callbacks.)
+ */
+static inline bool rcu_segcblist_restempty(struct rcu_segcblist *rsclp, int seg)
+{
+	return !*rsclp->tails[seg];
+}
+
+/*
+ * Does the specified rcu_segcblist structure contain callbacks that
+ * are ready to be invoked?
+ */
+static inline bool rcu_segcblist_ready_cbs(struct rcu_segcblist *rsclp)
+{
+	return rcu_segcblist_is_enabled(rsclp) &&
+	       &rsclp->head != rsclp->tails[RCU_DONE_TAIL];
+}
+
+/*
+ * Does the specified rcu_segcblist structure contain callbacks that
+ * are still pending, that is, not yet ready to be invoked?
+ */
+static inline bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp)
+{
+	return rcu_segcblist_is_enabled(rsclp) &&
+	       !rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL);
+}
+
+/*
+ * Dequeue and return the first ready-to-invoke callback.  If there
+ * are no ready-to-invoke callbacks, return NULL.  Disables interrupts
+ * to avoid interference.  Does not protect from interference from other
+ * CPUs or tasks.
+ */
+static inline struct rcu_head *
+rcu_segcblist_dequeue(struct rcu_segcblist *rsclp)
+{
+	unsigned long flags;
+	int i;
+	struct rcu_head *rhp;
+
+	local_irq_save(flags);
+	if (!rcu_segcblist_ready_cbs(rsclp)) {
+		local_irq_restore(flags);
+		return NULL;
+	}
+	rhp = rsclp->head;
+	BUG_ON(!rhp);
+	rsclp->head = rhp->next;
+	for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++) {
+		if (rsclp->tails[i] != &rhp->next)
+			break;
+		rsclp->tails[i] = &rsclp->head;
+	}
+	smp_mb(); /* Dequeue before decrement for rcu_barrier(). */
+	WRITE_ONCE(rsclp->len, rsclp->len - 1);
+	local_irq_restore(flags);
+	return rhp;
+}
+
+/*
+ * Account for the fact that a previously dequeued callback turned out
+ * to be marked as lazy.
+ */
+static inline void rcu_segcblist_dequeued_lazy(struct rcu_segcblist *rsclp)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	rsclp->len_lazy--;
+	local_irq_restore(flags);
+}
+
+/*
+ * Return a pointer to the first callback in the specified rcu_segcblist
+ * structure.  This is useful for diagnostics.
+ */
+static inline struct rcu_head *
+rcu_segcblist_first_cb(struct rcu_segcblist *rsclp)
+{
+	if (rcu_segcblist_is_enabled(rsclp))
+		return rsclp->head;
+	return NULL;
+}
+
+/*
+ * Return a pointer to the first pending callback in the specified
+ * rcu_segcblist structure.  This is useful just after posting a given
+ * callback -- if that callback is the first pending callback, then
+ * you cannot rely on someone else having already started up the required
+ * grace period.
+ */
+static inline struct rcu_head *
+rcu_segcblist_first_pend_cb(struct rcu_segcblist *rsclp)
+{
+	if (rcu_segcblist_is_enabled(rsclp))
+		return *rsclp->tails[RCU_DONE_TAIL];
+	return NULL;
+}
+
+/*
+ * Does the specified rcu_segcblist structure contain callbacks that
+ * have not yet been processed beyond having been posted, that is,
+ * does it contain callbacks in its last segment?
+ */
+static inline bool rcu_segcblist_new_cbs(struct rcu_segcblist *rsclp)
+{
+	return rcu_segcblist_is_enabled(rsclp) &&
+	       !rcu_segcblist_restempty(rsclp, RCU_NEXT_READY_TAIL);
+}
+
+/*
+ * Enqueue the specified callback onto the specified rcu_segcblist
+ * structure, updating accounting as needed.  Note that the ->len
+ * field may be accessed locklessly, hence the WRITE_ONCE().
+ * The ->len field is used by rcu_barrier() and friends to determine
+ * if it must post a callback on this structure, and it is OK
+ * for rcu_barrier() to sometimes post callbacks needlessly, but
+ * absolutely not OK for it to ever miss posting a callback.
+ */
+static inline void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
+					 struct rcu_head *rhp, bool lazy)
+{
+	WRITE_ONCE(rsclp->len, rsclp->len + 1); /* ->len sampled locklessly. */
+	if (lazy)
+		rsclp->len_lazy++;
+	smp_mb(); /* Ensure counts are updated before callback is enqueued. */
+	rhp->next = NULL;
+	*rsclp->tails[RCU_NEXT_TAIL] = rhp;
+	rsclp->tails[RCU_NEXT_TAIL] = &rhp->next;
+}
+
+/*
+ * Extract only the counts from the specified rcu_segcblist structure,
+ * and place them in the specified rcu_cblist structure.  This function
+ * supports both callback orphaning and invocation, hence the separation
+ * of counts and callbacks.  (Callbacks ready for invocation must be
+ * orphaned and adopted separately from pending callbacks, but counts
+ * apply to all callbacks.  Locking must be used to make sure that
+ * both orphaned-callbacks lists are consistent.)
+ */
+static inline void rcu_segcblist_extract_count(struct rcu_segcblist *rsclp,
+					       struct rcu_cblist *rclp)
+{
+	rclp->len_lazy += rsclp->len_lazy;
+	rclp->len += rsclp->len;
+	rsclp->len_lazy = 0;
+	WRITE_ONCE(rsclp->len, 0); /* ->len sampled locklessly. */
+}
+
+/*
+ * Extract only those callbacks ready to be invoked from the specified
+ * rcu_segcblist structure and place them in the specified rcu_cblist
+ * structure.
+ */
+static inline void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp,
+						  struct rcu_cblist *rclp)
+{
+	int i;
+
+	if (!rcu_segcblist_ready_cbs(rsclp))
+		return; /* Nothing to do. */
+	*rclp->tail = rsclp->head;
+	rsclp->head = *rsclp->tails[RCU_DONE_TAIL];
+	*rsclp->tails[RCU_DONE_TAIL] = NULL;
+	rclp->tail = rsclp->tails[RCU_DONE_TAIL];
+	for (i = RCU_CBLIST_NSEGS - 1; i >= RCU_DONE_TAIL; i--)
+		if (rsclp->tails[i] == rsclp->tails[RCU_DONE_TAIL])
+			rsclp->tails[i] = &rsclp->head;
+}
+
+/*
+ * Extract only those callbacks still pending (not yet ready to be
+ * invoked) from the specified rcu_segcblist structure and place them in
+ * the specified rcu_cblist structure.  Note that this loses information
+ * about any callbacks that might have been partway done waiting for
+ * their grace period.  Too bad!  They will have to start over.
+ */
+static inline void
+rcu_segcblist_extract_pend_cbs(struct rcu_segcblist *rsclp,
+			       struct rcu_cblist *rclp)
+{
+	int i;
+
+	if (!rcu_segcblist_pend_cbs(rsclp))
+		return; /* Nothing to do. */
+	*rclp->tail = *rsclp->tails[RCU_DONE_TAIL];
+	rclp->tail = rsclp->tails[RCU_NEXT_TAIL];
+	*rsclp->tails[RCU_DONE_TAIL] = NULL;
+	for (i = RCU_DONE_TAIL + 1; i < RCU_CBLIST_NSEGS; i++)
+		rsclp->tails[i] = rsclp->tails[RCU_DONE_TAIL];
+}
+
+/*
+ * Move the entire contents of the specified rcu_segcblist structure,
+ * counts, callbacks, and all, to the specified rcu_cblist structure.
+ * @@@ Why do we need this???  Moving early-boot CBs to NOCB lists?
+ * @@@ Memory barrier needed?  (Not if only used at boot time...)
+ */
+static inline void rcu_segcblist_extract_all(struct rcu_segcblist *rsclp,
+					     struct rcu_cblist *rclp)
+{
+	rcu_segcblist_extract_done_cbs(rsclp, rclp);
+	rcu_segcblist_extract_pend_cbs(rsclp, rclp);
+	rcu_segcblist_extract_count(rsclp, rclp);
+}
+
+/*
+ * Insert counts from the specified rcu_cblist structure in the
+ * specified rcu_segcblist structure.
+ */
+static inline void rcu_segcblist_insert_count(struct rcu_segcblist *rsclp,
+					      struct rcu_cblist *rclp)
+{
+	rsclp->len_lazy += rclp->len_lazy;
+	/* ->len sampled locklessly. */
+	WRITE_ONCE(rsclp->len, rsclp->len + rclp->len);
+	rclp->len_lazy = 0;
+	rclp->len = 0;
+}
+
+/*
+ * Move callbacks from the specified rcu_cblist to the beginning of the
+ * done-callbacks segment of the specified rcu_segcblist.
+ */
+static inline void rcu_segcblist_insert_done_cbs(struct rcu_segcblist *rsclp,
+						 struct rcu_cblist *rclp)
+{
+	int i;
+
+	if (!rclp->head)
+		return; /* No callbacks to move. */
+	*rclp->tail = rsclp->head;
+	rsclp->head = rclp->head;
+	for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++)
+		if (&rsclp->head == rsclp->tails[i])
+			rsclp->tails[i] = rclp->tail;
+		else
+			break;
+	rclp->head = NULL;
+	rclp->tail = &rclp->head;
+}
+
+/*
+ * Move callbacks from the specified rcu_cblist to the end of the
+ * new-callbacks segment of the specified rcu_segcblist.
+ */
+static inline void rcu_segcblist_insert_pend_cbs(struct rcu_segcblist *rsclp,
+						 struct rcu_cblist *rclp)
+{
+	if (!rclp->head)
+		return; /* Nothing to do. */
+	*rsclp->tails[RCU_NEXT_TAIL] = rclp->head;
+	rsclp->tails[RCU_NEXT_TAIL] = rclp->tail;
+	rclp->head = NULL;
+	rclp->tail = &rclp->head;
+}
+
+/*
+ * Advance the callbacks in the specified rcu_segcblist structure based
+ * on the current value passed in for the grace-period counter.
+ */
+static inline void rcu_segcblist_advance(struct rcu_segcblist *rsclp,
+					 unsigned long seq)
+{
+	int i, j;
+
+	WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
+	WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL));
+
+	/*
+	 * Find all callbacks whose ->gp_seq numbers indicate that they
+	 * are ready to invoke, and put them into the RCU_DONE_TAIL segment.
+	 */
+	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
+		if (ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
+			break;
+		rsclp->tails[RCU_DONE_TAIL] = rsclp->tails[i];
+	}
+
+	/* If no callbacks moved, nothing more need be done. */
+	if (i == RCU_WAIT_TAIL)
+		return;
+
+	/* Clean up tail pointers that might have been misordered above. */
+	for (j = RCU_WAIT_TAIL; j < i; j++)
+		rsclp->tails[j] = rsclp->tails[RCU_DONE_TAIL];
+
+	/*
+	 * Callbacks moved, so clean up the misordered ->tails[] pointers
+	 * that now point into the middle of the list of ready-to-invoke
+	 * callbacks.  The overall effect is to copy down the later pointers
+	 * into the gap that was created by the now-ready segments.
+	 */
+	for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
+		if (rsclp->tails[j] == rsclp->tails[RCU_NEXT_TAIL])
+			break;  /* No more callbacks. */
+		rsclp->tails[j] = rsclp->tails[i];
+		rsclp->gp_seq[j] = rsclp->gp_seq[i];
+	}
+}
+
+/*
+ * "Accelerate" callbacks based on more-accurate grace-period information.
+ * The reason for this is that RCU does not synchronize the beginnings and
+ * ends of grace periods, and that callbacks are posted locally.  This in
+ * turn means that the callbacks must be labelled conservatively early
+ * on, as getting exact information would degrade both performance and
+ * scalability.  When more accurate grace-period information becomes
+ * available, previously posted callbacks can be "accelerated", marking
+ * them to complete at the end of the earlier grace period.
+ *
+ * This function operates on an rcu_segcblist structure, and also the
+ * grace-period sequence number at which new callbacks would become
+ * ready to invoke.
+ */
+static inline bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp,
+					    unsigned long seq)
+{
+	int i;
+
+	WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
+	WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL));
+
+	/*
+	 * Find the segment preceding the oldest segment of callbacks
+	 * whose ->gp_seq[] completion is at or after that passed in via
+	 * "seq", skipping any empty segments.  This oldest segment, along
+	 * with any later segments, can be merged in with any newly arrived
+	 * callbacks in the RCU_NEXT_TAIL segment, and assigned "seq"
+	 * as their ->gp_seq[] grace-period completion sequence number.
+	 */
+	for (i = RCU_NEXT_READY_TAIL; i > RCU_DONE_TAIL; i--)
+		if (rsclp->tails[i] != rsclp->tails[i - 1] &&
+		    ULONG_CMP_LT(rsclp->gp_seq[i], seq))
+			break;
+
+	/*
+	 * If all the segments contain callbacks that correspond to
+	 * earlier grace-period sequence numbers than "seq", leave.
+	 * Assuming that the rcu_segcblist structure has enough
+	 * segments in its arrays, this can only happen if some of
+	 * the non-done segments contain callbacks that really are
+	 * ready to invoke.  This situation will get straightened
+	 * out by the next call to rcu_segcblist_advance().
+	 *
+	 * Also advance to the oldest segment of callbacks whose
+	 * ->gp_seq[] completion is at or after that passed in via "seq",
+	 * skipping any empty segments.
+	 */
+	if (++i >= RCU_NEXT_TAIL)
+		return false;
+
+	/*
+	 * Merge all later callbacks, including newly arrived callbacks,
+	 * into the segment located by the for-loop above.  Assign "seq"
+	 * as the ->gp_seq[] value in order to correctly handle the case
+	 * where there were no pending callbacks in the rcu_segcblist
+	 * structure other than in the RCU_NEXT_TAIL segment.
+	 */
+	for (; i < RCU_NEXT_TAIL; i++) {
+		rsclp->tails[i] = rsclp->tails[RCU_NEXT_TAIL];
+		rsclp->gp_seq[i] = seq;
+	}
+	return true;
+}
+
+/*
+ * Scan the specified rcu_segcblist structure for callbacks that need
+ * a grace period later than the one specified by "seq".  We don't look
+ * at the RCU_DONE_TAIL or RCU_NEXT_TAIL segments because they don't
+ * have a grace-period sequence number.
+ */
+static inline bool rcu_segcblist_future_gp_needed(struct rcu_segcblist *rsclp,
+						  unsigned long seq)
+{
+	int i;
+
+	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
+		if (rsclp->tails[i - 1] != rsclp->tails[i] &&
+		    ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
+			return true;
+	return false;
+}
+
+/*
+ * Interim function to return rcu_segcblist head pointer.  Longer term, the
+ * rcu_segcblist will be used more pervasively, removing the need for this
+ * function.
+ */
+static inline struct rcu_head *rcu_segcblist_head(struct rcu_segcblist *rsclp)
+{
+	return rsclp->head;
+}
+
+/*
+ * Interim function to return rcu_segcblist head pointer.  Longer term, the
+ * rcu_segcblist will be used more pervasively, removing the need for this
+ * function.
+ */
+static inline struct rcu_head **rcu_segcblist_tail(struct rcu_segcblist *rsclp)
+{
+	WARN_ON_ONCE(rcu_segcblist_empty(rsclp));
+	return rsclp->tails[RCU_NEXT_TAIL];
+}
+
+#endif /* __KERNEL_RCU_SEGCBLIST_H */
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 047ac8c28a4e..ad154a7bc114 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -22,7 +22,7 @@
  *	   Lai Jiangshan <laijs@cn.fujitsu.com>
  *
  * For detailed explanation of Read-Copy Update mechanism see -
- * 		Documentation/RCU/ *.txt
+ *		Documentation/RCU/ *.txt
  *
  */
 
@@ -32,31 +32,20 @@
 #include <linux/mutex.h>
 #include <linux/rcupdate.h>
 #include <linux/workqueue.h>
+#include <linux/rcu_segcblist.h>
 
 struct srcu_array {
 	unsigned long lock_count[2];
 	unsigned long unlock_count[2];
 };
 
-struct rcu_batch {
-	struct rcu_head *head, **tail;
-};
-
-#define RCU_BATCH_INIT(name) { NULL, &(name.head) }
-
 struct srcu_struct {
 	unsigned long completed;
 	unsigned long srcu_gp_seq;
 	struct srcu_array __percpu *per_cpu_ref;
-	spinlock_t queue_lock; /* protect ->batch_queue, ->running */
+	spinlock_t queue_lock; /* protect ->srcu_cblist, ->srcu_state */
 	int srcu_state;
-	/* callbacks just queued */
-	struct rcu_batch batch_queue;
-	/* callbacks try to do the first check_zero */
-	struct rcu_batch batch_check0;
-	/* callbacks done with the first check_zero and the flip */
-	struct rcu_batch batch_check1;
-	struct rcu_batch batch_done;
+	struct rcu_segcblist srcu_cblist;
 	struct delayed_work work;
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map dep_map;
@@ -97,10 +86,7 @@ void process_srcu(struct work_struct *work);
 		.per_cpu_ref = &name##_srcu_array,			\
 		.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock),	\
 		.srcu_state = SRCU_STATE_IDLE,				\
-		.batch_queue = RCU_BATCH_INIT(name.batch_queue),	\
-		.batch_check0 = RCU_BATCH_INIT(name.batch_check0),	\
-		.batch_check1 = RCU_BATCH_INIT(name.batch_check1),	\
-		.batch_done = RCU_BATCH_INIT(name.batch_done),		\
+		.srcu_cblist = RCU_SEGCBLIST_INITIALIZER(name.srcu_cblist),\
 		.work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
 		__SRCU_DEP_MAP_INIT(name)				\
 	}
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 0bc1313c49e2..a943b42a9cf7 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -87,6 +87,12 @@ static inline unsigned long rcu_seq_snap(unsigned long *sp)
 	return s;
 }
 
+/* Return the current value the update side's sequence number, no ordering. */
+static inline unsigned long rcu_seq_current(unsigned long *sp)
+{
+	return READ_ONCE(*sp);
+}
+
 /*
  * Given a snapshot from rcu_seq_snap(), determine whether or not a
  * full update-side operation has occurred.
diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
deleted file mode 100644
index c32d13b368ac..000000000000
--- a/kernel/rcu/rcu_segcblist.h
+++ /dev/null
@@ -1,671 +0,0 @@
-/*
- * RCU segmented callback lists
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, you can access it online at
- * http://www.gnu.org/licenses/gpl-2.0.html.
- *
- * Copyright IBM Corporation, 2017
- *
- * Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
- */
-
-#ifndef __KERNEL_RCU_SEGCBLIST_H
-#define __KERNEL_RCU_SEGCBLIST_H
-
-/* Simple unsegmented callback lists. */
-struct rcu_cblist {
-	struct rcu_head *head;
-	struct rcu_head **tail;
-	long len;
-	long len_lazy;
-};
-
-#define RCU_CBLIST_INITIALIZER(n) { .head = NULL, .tail = &n.head }
-
-/* Initialize simple callback list. */
-static inline void rcu_cblist_init(struct rcu_cblist *rclp)
-{
-	rclp->head = NULL;
-	rclp->tail = &rclp->head;
-	rclp->len = 0;
-	rclp->len_lazy = 0;
-}
-
-/* Is simple callback list empty? */
-static inline bool rcu_cblist_empty(struct rcu_cblist *rclp)
-{
-	return !rclp->head;
-}
-
-/* Return number of callbacks in simple callback list. */
-static inline long rcu_cblist_n_cbs(struct rcu_cblist *rclp)
-{
-	return rclp->len;
-}
-
-/* Return number of lazy callbacks in simple callback list. */
-static inline long rcu_cblist_n_lazy_cbs(struct rcu_cblist *rclp)
-{
-	return rclp->len_lazy;
-}
-
-/*
- * Debug function to actually count the number of callbacks.
- * If the number exceeds the limit specified, return -1.
- */
-static inline long rcu_cblist_count_cbs(struct rcu_cblist *rclp, long lim)
-{
-	int cnt = 0;
-	struct rcu_head **rhpp = &rclp->head;
-
-	for (;;) {
-		if (!*rhpp)
-			return cnt;
-		if (++cnt > lim)
-			return -1;
-		rhpp = &(*rhpp)->next;
-	}
-}
-
-/*
- * Dequeue the oldest rcu_head structure from the specified callback
- * list.  This function assumes that the callback is non-lazy, but
- * the caller can later invoke rcu_cblist_dequeued_lazy() if it
- * finds otherwise (and if it cares about laziness).  This allows
- * different users to have different ways of determining laziness.
- */
-static inline struct rcu_head *rcu_cblist_dequeue(struct rcu_cblist *rclp)
-{
-	struct rcu_head *rhp;
-
-	rhp = rclp->head;
-	if (!rhp)
-		return NULL;
-	prefetch(rhp);
-	rclp->len--;
-	rclp->head = rhp->next;
-	if (!rclp->head)
-		rclp->tail = &rclp->head;
-	return rhp;
-}
-
-/*
- * Account for the fact that a previously dequeued callback turned out
- * to be marked as lazy.
- */
-static inline void rcu_cblist_dequeued_lazy(struct rcu_cblist *rclp)
-{
-	rclp->len_lazy--;
-}
-
-/*
- * Interim function to return rcu_cblist head pointer.  Longer term, the
- * rcu_cblist will be used more pervasively, removing the need for this
- * function.
- */
-static inline struct rcu_head *rcu_cblist_head(struct rcu_cblist *rclp)
-{
-	return rclp->head;
-}
-
-/*
- * Interim function to return rcu_cblist head pointer.  Longer term, the
- * rcu_cblist will be used more pervasively, removing the need for this
- * function.
- */
-static inline struct rcu_head **rcu_cblist_tail(struct rcu_cblist *rclp)
-{
-	WARN_ON_ONCE(rcu_cblist_empty(rclp));
-	return rclp->tail;
-}
-
-/* Complicated segmented callback lists.  ;-) */
-
-/*
- * Index values for segments in rcu_segcblist structure.
- *
- * The segments are as follows:
- *
- * [head, *tails[RCU_DONE_TAIL]):
- *	Callbacks whose grace period has elapsed, and thus can be invoked.
- * [*tails[RCU_DONE_TAIL], *tails[RCU_WAIT_TAIL]):
- *	Callbacks waiting for the current GP from the current CPU's viewpoint.
- * [*tails[RCU_WAIT_TAIL], *tails[RCU_NEXT_READY_TAIL]):
- *	Callbacks that arrived before the next GP started, again from
- *	the current CPU's viewpoint.  These can be handled by the next GP.
- * [*tails[RCU_NEXT_READY_TAIL], *tails[RCU_NEXT_TAIL]):
- *	Callbacks that might have arrived after the next GP started.
- *	There is some uncertainty as to when a given GP starts and
- *	ends, but a CPU knows the exact times if it is the one starting
- *	or ending the GP.  Other CPUs know that the previous GP ends
- *	before the next one starts.
- *
- * Note that RCU_WAIT_TAIL cannot be empty unless RCU_NEXT_READY_TAIL is also
- * empty.
- *
- * The ->gp_seq[] array contains the grace-period number at which the
- * corresponding segment of callbacks will be ready to invoke.  A given
- * element of this array is meaningful only when the corresponding segment
- * is non-empty, and it is never valid for RCU_DONE_TAIL (whose callbacks
- * are already ready to invoke) or for RCU_NEXT_TAIL (whose callbacks have
- * not yet been assigned a grace-period number).
- */
-#define RCU_DONE_TAIL		0	/* Also RCU_WAIT head. */
-#define RCU_WAIT_TAIL		1	/* Also RCU_NEXT_READY head. */
-#define RCU_NEXT_READY_TAIL	2	/* Also RCU_NEXT head. */
-#define RCU_NEXT_TAIL		3
-#define RCU_CBLIST_NSEGS	4
-
-struct rcu_segcblist {
-	struct rcu_head *head;
-	struct rcu_head **tails[RCU_CBLIST_NSEGS];
-	unsigned long gp_seq[RCU_CBLIST_NSEGS];
-	long len;
-	long len_lazy;
-};
-
-/*
- * Initialize an rcu_segcblist structure.
- */
-static inline void rcu_segcblist_init(struct rcu_segcblist *rsclp)
-{
-	int i;
-
-	BUILD_BUG_ON(RCU_NEXT_TAIL + 1 != ARRAY_SIZE(rsclp->gp_seq));
-	BUILD_BUG_ON(ARRAY_SIZE(rsclp->tails) != ARRAY_SIZE(rsclp->gp_seq));
-	rsclp->head = NULL;
-	for (i = 0; i < RCU_CBLIST_NSEGS; i++)
-		rsclp->tails[i] = &rsclp->head;
-	rsclp->len = 0;
-	rsclp->len_lazy = 0;
-}
-
-/*
- * Is the specified rcu_segcblist structure empty?
- *
- * But careful!  The fact that the ->head field is NULL does not
- * necessarily imply that there are no callbacks associated with
- * this structure.  When callbacks are being invoked, they are
- * removed as a group.  If callback invocation must be preempted,
- * the remaining callbacks will be added back to the list.  Either
- * way, the counts are updated later.
- *
- * So it is often the case that rcu_segcblist_n_cbs() should be used
- * instead.
- */
-static inline bool rcu_segcblist_empty(struct rcu_segcblist *rsclp)
-{
-	return !rsclp->head;
-}
-
-/* Return number of callbacks in segmented callback list. */
-static inline long rcu_segcblist_n_cbs(struct rcu_segcblist *rsclp)
-{
-	return READ_ONCE(rsclp->len);
-}
-
-/* Return number of lazy callbacks in segmented callback list. */
-static inline long rcu_segcblist_n_lazy_cbs(struct rcu_segcblist *rsclp)
-{
-	return rsclp->len_lazy;
-}
-
-/* Return number of lazy callbacks in segmented callback list. */
-static inline long rcu_segcblist_n_nonlazy_cbs(struct rcu_segcblist *rsclp)
-{
-	return rsclp->len - rsclp->len_lazy;
-}
-
-/*
- * Is the specified rcu_segcblist enabled, for example, not corresponding
- * to an offline or callback-offloaded CPU?
- */
-static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp)
-{
-	return !!rsclp->tails[RCU_NEXT_TAIL];
-}
-
-/*
- * Disable the specified rcu_segcblist structure, so that callbacks can
- * no longer be posted to it.  This structure must be empty.
- */
-static inline void rcu_segcblist_disable(struct rcu_segcblist *rsclp)
-{
-	WARN_ON_ONCE(!rcu_segcblist_empty(rsclp));
-	WARN_ON_ONCE(rcu_segcblist_n_cbs(rsclp));
-	WARN_ON_ONCE(rcu_segcblist_n_lazy_cbs(rsclp));
-	rsclp->tails[RCU_NEXT_TAIL] = NULL;
-}
-
-/*
- * Is the specified segment of the specified rcu_segcblist structure
- * empty of callbacks?
- */
-static inline bool rcu_segcblist_segempty(struct rcu_segcblist *rsclp, int seg)
-{
-	if (seg == RCU_DONE_TAIL)
-		return &rsclp->head == rsclp->tails[RCU_DONE_TAIL];
-	return rsclp->tails[seg - 1] == rsclp->tails[seg];
-}
-
-/*
- * Are all segments following the specified segment of the specified
- * rcu_segcblist structure empty of callbacks?  (The specified
- * segment might well contain callbacks.)
- */
-static inline bool rcu_segcblist_restempty(struct rcu_segcblist *rsclp, int seg)
-{
-	return !*rsclp->tails[seg];
-}
-
-/*
- * Does the specified rcu_segcblist structure contain callbacks that
- * are ready to be invoked?
- */
-static inline bool rcu_segcblist_ready_cbs(struct rcu_segcblist *rsclp)
-{
-	return rcu_segcblist_is_enabled(rsclp) &&
-	       &rsclp->head != rsclp->tails[RCU_DONE_TAIL];
-}
-
-/*
- * Does the specified rcu_segcblist structure contain callbacks that
- * are still pending, that is, not yet ready to be invoked?
- */
-static inline bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp)
-{
-	return rcu_segcblist_is_enabled(rsclp) &&
-	       !rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL);
-}
-
-/*
- * Dequeue and return the first ready-to-invoke callback.  If there
- * are no ready-to-invoke callbacks, return NULL.  Disables interrupts
- * to avoid interference.  Does not protect from interference from other
- * CPUs or tasks.
- */
-static inline struct rcu_head *
-rcu_segcblist_dequeue(struct rcu_segcblist *rsclp)
-{
-	unsigned long flags;
-	int i;
-	struct rcu_head *rhp;
-
-	local_irq_save(flags);
-	if (!rcu_segcblist_ready_cbs(rsclp)) {
-		local_irq_restore(flags);
-		return NULL;
-	}
-	rhp = rsclp->head;
-	BUG_ON(!rhp);
-	rsclp->head = rhp->next;
-	for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++) {
-		if (rsclp->tails[i] != &rhp->next)
-			break;
-		rsclp->tails[i] = &rsclp->head;
-	}
-	smp_mb(); /* Dequeue before decrement for rcu_barrier(). */
-	WRITE_ONCE(rsclp->len, rsclp->len - 1);
-	local_irq_restore(flags);
-	return rhp;
-}
-
-/*
- * Account for the fact that a previously dequeued callback turned out
- * to be marked as lazy.
- */
-static inline void rcu_segcblist_dequeued_lazy(struct rcu_segcblist *rsclp)
-{
-	unsigned long flags;
-
-	local_irq_save(flags);
-	rsclp->len_lazy--;
-	local_irq_restore(flags);
-}
-
-/*
- * Return a pointer to the first callback in the specified rcu_segcblist
- * structure.  This is useful for diagnostics.
- */
-static inline struct rcu_head *
-rcu_segcblist_first_cb(struct rcu_segcblist *rsclp)
-{
-	if (rcu_segcblist_is_enabled(rsclp))
-	       return rsclp->head;
-	return NULL;
-}
-
-/*
- * Return a pointer to the first pending callback in the specified
- * rcu_segcblist structure.  This is useful just after posting a given
- * callback -- if that callback is the first pending callback, then
- * you cannot rely on someone else having already started up the required
- * grace period.
- */
-static inline struct rcu_head *
-rcu_segcblist_first_pend_cb(struct rcu_segcblist *rsclp)
-{
-	if (rcu_segcblist_is_enabled(rsclp))
-	       return *rsclp->tails[RCU_DONE_TAIL];
-	return NULL;
-}
-
-/*
- * Does the specified rcu_segcblist structure contain callbacks that
- * have not yet been processed beyond having been posted, that is,
- * does it contain callbacks in its last segment?
- */
-static inline bool rcu_segcblist_new_cbs(struct rcu_segcblist *rsclp)
-{
-	return rcu_segcblist_is_enabled(rsclp) &&
-	       !rcu_segcblist_restempty(rsclp, RCU_NEXT_READY_TAIL);
-}
-
-/*
- * Enqueue the specified callback onto the specified rcu_segcblist
- * structure, updating accounting as needed.  Note that the ->len
- * field may be accessed locklessly, hence the WRITE_ONCE().
- * The ->len field is used by rcu_barrier() and friends to determine
- * if it must post a callback on this structure, and it is OK
- * for rcu_barrier() to sometimes post callbacks needlessly, but
- * absolutely not OK for it to ever miss posting a callback.
- */
-static inline void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
-					 struct rcu_head *rhp, bool lazy)
-{
-	WRITE_ONCE(rsclp->len, rsclp->len + 1); /* ->len sampled locklessly. */
-	if (lazy)
-		rsclp->len_lazy++;
-	smp_mb(); /* Ensure counts are updated before callback is enqueued. */
-	rhp->next = NULL;
-	*rsclp->tails[RCU_NEXT_TAIL] = rhp;
-	rsclp->tails[RCU_NEXT_TAIL] = &rhp->next;
-}
-
-/*
- * Extract only the counts from the specified rcu_segcblist structure,
- * and place them in the specified rcu_cblist structure.  This function
- * supports both callback orphaning and invocation, hence the separation
- * of counts and callbacks.  (Callbacks ready for invocation must be
- * orphaned and adopted separately from pending callbacks, but counts
- * apply to all callbacks.  Locking must be used to make sure that
- * both orphaned-callbacks lists are consistent.)
- */
-static inline void rcu_segcblist_extract_count(struct rcu_segcblist *rsclp,
-					       struct rcu_cblist *rclp)
-{
-	rclp->len_lazy += rsclp->len_lazy;
-	rclp->len += rsclp->len;
-	rsclp->len_lazy = 0;
-	WRITE_ONCE(rsclp->len, 0); /* ->len sampled locklessly. */
-}
-
-/*
- * Extract only those callbacks ready to be invoked from the specified
- * rcu_segcblist structure and place them in the specified rcu_cblist
- * structure.
- */
-static inline void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp,
-						  struct rcu_cblist *rclp)
-{
-	int i;
-
-	if (!rcu_segcblist_ready_cbs(rsclp))
-		return; /* Nothing to do. */
-	*rclp->tail = rsclp->head;
-	rsclp->head = *rsclp->tails[RCU_DONE_TAIL];
-	*rsclp->tails[RCU_DONE_TAIL] = NULL;
-	rclp->tail = rsclp->tails[RCU_DONE_TAIL];
-	for (i = RCU_CBLIST_NSEGS - 1; i >= RCU_DONE_TAIL; i--)
-		if (rsclp->tails[i] == rsclp->tails[RCU_DONE_TAIL])
-			rsclp->tails[i] = &rsclp->head;
-}
-
-/*
- * Extract only those callbacks still pending (not yet ready to be
- * invoked) from the specified rcu_segcblist structure and place them in
- * the specified rcu_cblist structure.  Note that this loses information
- * about any callbacks that might have been partway done waiting for
- * their grace period.  Too bad!  They will have to start over.
- */
-static inline void
-rcu_segcblist_extract_pend_cbs(struct rcu_segcblist *rsclp,
-			       struct rcu_cblist *rclp)
-{
-	int i;
-
-	if (!rcu_segcblist_pend_cbs(rsclp))
-		return; /* Nothing to do. */
-	*rclp->tail = *rsclp->tails[RCU_DONE_TAIL];
-	rclp->tail = rsclp->tails[RCU_NEXT_TAIL];
-	*rsclp->tails[RCU_DONE_TAIL] = NULL;
-	for (i = RCU_DONE_TAIL + 1; i < RCU_CBLIST_NSEGS; i++)
-		rsclp->tails[i] = rsclp->tails[RCU_DONE_TAIL];
-}
-
-/*
- * Move the entire contents of the specified rcu_segcblist structure,
- * counts, callbacks, and all, to the specified rcu_cblist structure.
- * @@@ Why do we need this???  Moving early-boot CBs to NOCB lists?
- * @@@ Memory barrier needed?  (Not if only used at boot time...)
- */
-static inline void rcu_segcblist_extract_all(struct rcu_segcblist *rsclp,
-					     struct rcu_cblist *rclp)
-{
-	rcu_segcblist_extract_done_cbs(rsclp, rclp);
-	rcu_segcblist_extract_pend_cbs(rsclp, rclp);
-	rcu_segcblist_extract_count(rsclp, rclp);
-}
-
-/*
- * Insert counts from the specified rcu_cblist structure in the
- * specified rcu_segcblist structure.
- */
-static inline void rcu_segcblist_insert_count(struct rcu_segcblist *rsclp,
-					      struct rcu_cblist *rclp)
-{
-	
-	rsclp->len_lazy += rclp->len_lazy;
-	/* ->len sampled locklessly. */
-	WRITE_ONCE(rsclp->len, rsclp->len + rclp->len);
-	rclp->len_lazy = 0;
-	rclp->len = 0;
-}
-
-/*
- * Move callbacks from the specified rcu_cblist to the beginning of the
- * done-callbacks segment of the specified rcu_segcblist.
- */
-static inline void rcu_segcblist_insert_done_cbs(struct rcu_segcblist *rsclp,
-						 struct rcu_cblist *rclp)
-{
-	int i;
-
-	if (!rclp->head)
-		return; /* No callbacks to move. */
-	*rclp->tail = rsclp->head;
-	rsclp->head = rclp->head;
-	for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++)
-		if (&rsclp->head == rsclp->tails[i])
-			rsclp->tails[i] = rclp->tail;
-		else
-			break;
-	rclp->head = NULL;
-	rclp->tail = &rclp->head;
-}
-
-/*
- * Move callbacks from the specified rcu_cblist to the end of the
- * new-callbacks segment of the specified rcu_segcblist.
- */
-static inline void rcu_segcblist_insert_pend_cbs(struct rcu_segcblist *rsclp,
-						 struct rcu_cblist *rclp)
-{
-	if (!rclp->head)
-		return; /* Nothing to do. */
-	*rsclp->tails[RCU_NEXT_TAIL] = rclp->head;
-	rsclp->tails[RCU_NEXT_TAIL] = rclp->tail;
-	rclp->head = NULL;
-	rclp->tail = &rclp->head;
-}
-
-/*
- * Advance the callbacks in the specified rcu_segcblist structure based
- * on the current value passed in for the grace-period counter.
- */
-static inline void rcu_segcblist_advance(struct rcu_segcblist *rsclp,
-					 unsigned long seq)
-{
-	int i, j;
-
-	WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
-	WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL));
-
-	/*
-	 * Find all callbacks whose ->gp_seq numbers indicate that they
-	 * are ready to invoke, and put them into the RCU_DONE_TAIL segment.
-	 */
-	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
-		if (ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
-			break;
-		rsclp->tails[RCU_DONE_TAIL] = rsclp->tails[i];
-	}
-
-	/* If no callbacks moved, nothing more need be done. */
-	if (i == RCU_WAIT_TAIL)
-		return;
-
-	/* Clean up tail pointers that might have been misordered above. */
-	for (j = RCU_WAIT_TAIL; j < i; j++)
-		rsclp->tails[j] = rsclp->tails[RCU_DONE_TAIL];
-
-	/*
-	 * Callbacks moved, so clean up the misordered ->tails[] pointers
-	 * that now point into the middle of the list of ready-to-invoke
-	 * callbacks.  The overall effect is to copy down the later pointers
-	 * into the gap that was created by the now-ready segments.
-	 */
-	for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
-		if (rsclp->tails[j] == rsclp->tails[RCU_NEXT_TAIL])
-			break;  /* No more callbacks. */
-		rsclp->tails[j] = rsclp->tails[i];
-		rsclp->gp_seq[j] = rsclp->gp_seq[i];
-	}
-}
-
-/*
- * "Accelerate" callbacks based on more-accurate grace-period information.
- * The reason for this is that RCU does not synchronize the beginnings and
- * ends of grace periods, and that callbacks are posted locally.  This in
- * turn means that the callbacks must be labelled conservatively early
- * on, as getting exact information would degrade both performance and
- * scalability.  When more accurate grace-period information becomes
- * available, previously posted callbacks can be "accelerated", marking
- * them to complete at the end of the earlier grace period.
- *
- * This function operates on an rcu_segcblist structure, and also the
- * grace-period sequence number at which new callbacks would become
- * ready to invoke.
- */
-static inline bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp,
-					    unsigned long seq)
-{
-	int i;
-
-	WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
-	WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL));
-
-	/*
-	 * Find the segment preceding the oldest segment of callbacks
-	 * whose ->gp_seq[] completion is at or after that passed in via
-	 * "seq", skipping any empty segments.  This oldest segment, along
-	 * with any later segments, can be merged in with any newly arrived
-	 * callbacks in the RCU_NEXT_TAIL segment, and assigned "seq"
-	 * as their ->gp_seq[] grace-period completion sequence number.
-	 */
-	for (i = RCU_NEXT_READY_TAIL; i > RCU_DONE_TAIL; i--)
-		if (rsclp->tails[i] != rsclp->tails[i - 1] &&
-		    ULONG_CMP_LT(rsclp->gp_seq[i], seq))
-			break;
-
-	/*
-	 * If all the segments contain callbacks that correspond to
-	 * earlier grace-period sequence numbers than "seq", leave.
-	 * Assuming that the rcu_segcblist structure has enough
-	 * segments in its arrays, this can only happen if some of
-	 * the non-done segments contain callbacks that really are
-	 * ready to invoke.  This situation will get straightened
-	 * out by the next call to rcu_segcblist_advance().
-	 *
-	 * Also advance to the oldest segment of callbacks whose
-	 * ->gp_seq[] completion is at or after that passed in via "seq",
-	 * skipping any empty segments.
-	 */
-	if (++i >= RCU_NEXT_TAIL)
-		return false;
-
-	/*
-	 * Merge all later callbacks, including newly arrived callbacks,
-	 * into the segment located by the for-loop above.  Assign "seq"
-	 * as the ->gp_seq[] value in order to correctly handle the case
-	 * where there were no pending callbacks in the rcu_segcblist
-	 * structure other than in the RCU_NEXT_TAIL segment.
-	 */
-	for (; i < RCU_NEXT_TAIL; i++) {
-		rsclp->tails[i] = rsclp->tails[RCU_NEXT_TAIL];
-		rsclp->gp_seq[i] = seq;
-	}
-	return true;
-}
-
-/*
- * Scan the specified rcu_segcblist structure for callbacks that need
- * a grace period later than the one specified by "seq".  We don't look
- * at the RCU_DONE_TAIL or RCU_NEXT_TAIL segments because they don't
- * have a grace-period sequence number.
- */
-static inline bool rcu_segcblist_future_gp_needed(struct rcu_segcblist *rsclp,
-						  unsigned long seq)
-{
-	int i;
-
-	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
-		if (rsclp->tails[i - 1] != rsclp->tails[i] &&
-		    ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
-		    	return true;
-	return false;
-}
-
-/*
- * Interim function to return rcu_segcblist head pointer.  Longer term, the
- * rcu_segcblist will be used more pervasively, removing the need for this
- * function.
- */
-static inline struct rcu_head *rcu_segcblist_head(struct rcu_segcblist *rsclp)
-{
-	return rsclp->head;
-}
-
-/*
- * Interim function to return rcu_segcblist head pointer.  Longer term, the
- * rcu_segcblist will be used more pervasively, removing the need for this
- * function.
- */
-static inline struct rcu_head **rcu_segcblist_tail(struct rcu_segcblist *rsclp)
-{
-	WARN_ON_ONCE(rcu_segcblist_empty(rsclp));
-	return rsclp->tails[RCU_NEXT_TAIL];
-}
-
-#endif /* __KERNEL_RCU_SEGCBLIST_H */
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index ed7c3d082b9f..132cd57c07f1 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -22,7 +22,7 @@
  *	   Lai Jiangshan <laijs@cn.fujitsu.com>
  *
  * For detailed explanation of Read-Copy Update mechanism see -
- * 		Documentation/RCU/ *.txt
+ *		Documentation/RCU/ *.txt
  *
  */
 
@@ -38,85 +38,13 @@
 
 #include "rcu.h"
 
-/*
- * Initialize an rcu_batch structure to empty.
- */
-static inline void rcu_batch_init(struct rcu_batch *b)
-{
-	b->head = NULL;
-	b->tail = &b->head;
-}
-
-/*
- * Enqueue a callback onto the tail of the specified rcu_batch structure.
- */
-static inline void rcu_batch_queue(struct rcu_batch *b, struct rcu_head *head)
-{
-	*b->tail = head;
-	b->tail = &head->next;
-}
-
-/*
- * Is the specified rcu_batch structure empty?
- */
-static inline bool rcu_batch_empty(struct rcu_batch *b)
-{
-	return b->tail == &b->head;
-}
-
-/*
- * Are all batches empty for the specified srcu_struct?
- */
-static inline bool rcu_all_batches_empty(struct srcu_struct *sp)
-{
-	return rcu_batch_empty(&sp->batch_done) &&
-	       rcu_batch_empty(&sp->batch_check1) &&
-	       rcu_batch_empty(&sp->batch_check0) &&
-	       rcu_batch_empty(&sp->batch_queue);
-}
-
-/*
- * Remove the callback at the head of the specified rcu_batch structure
- * and return a pointer to it, or return NULL if the structure is empty.
- */
-static inline struct rcu_head *rcu_batch_dequeue(struct rcu_batch *b)
-{
-	struct rcu_head *head;
-
-	if (rcu_batch_empty(b))
-		return NULL;
-
-	head = b->head;
-	b->head = head->next;
-	if (b->tail == &head->next)
-		rcu_batch_init(b);
-
-	return head;
-}
-
-/*
- * Move all callbacks from the rcu_batch structure specified by "from" to
- * the structure specified by "to".
- */
-static inline void rcu_batch_move(struct rcu_batch *to, struct rcu_batch *from)
-{
-	if (!rcu_batch_empty(from)) {
-		*to->tail = from->head;
-		to->tail = from->tail;
-		rcu_batch_init(from);
-	}
-}
-
 static int init_srcu_struct_fields(struct srcu_struct *sp)
 {
 	sp->completed = 0;
 	sp->srcu_gp_seq = 0;
 	spin_lock_init(&sp->queue_lock);
 	sp->srcu_state = SRCU_STATE_IDLE;
-	rcu_batch_init(&sp->batch_queue);
-	rcu_batch_init(&sp->batch_check0);
-	rcu_batch_init(&sp->batch_check1);
-	rcu_batch_init(&sp->batch_done);
+	rcu_segcblist_init(&sp->srcu_cblist);
 	INIT_DELAYED_WORK(&sp->work, process_srcu);
 	sp->per_cpu_ref = alloc_percpu(struct srcu_array);
 	return sp->per_cpu_ref ? 0 : -ENOMEM;
@@ -262,7 +190,7 @@ void cleanup_srcu_struct(struct srcu_struct *sp)
 {
 	if (WARN_ON(srcu_readers_active(sp)))
 		return; /* Leakage unless caller handles error. */
-	if (WARN_ON(!rcu_all_batches_empty(sp)))
+	if (WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist)))
 		return; /* Leakage unless caller handles error. */
 	flush_delayed_work(&sp->work);
 	if (WARN_ON(READ_ONCE(sp->srcu_state) != SRCU_STATE_IDLE))
@@ -318,6 +246,8 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
  */
 static void srcu_gp_start(struct srcu_struct *sp)
 {
+	rcu_segcblist_accelerate(&sp->srcu_cblist,
+				 rcu_seq_snap(&sp->srcu_gp_seq));
 	WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
 	rcu_seq_start(&sp->srcu_gp_seq);
 }
@@ -365,6 +295,11 @@ static void srcu_gp_end(struct srcu_struct *sp)
 {
 	rcu_seq_end(&sp->srcu_gp_seq);
 	WRITE_ONCE(sp->srcu_state, SRCU_STATE_DONE);
+
+	spin_lock_irq(&sp->queue_lock);
+	rcu_segcblist_advance(&sp->srcu_cblist,
+			      rcu_seq_current(&sp->srcu_gp_seq));
+	spin_unlock_irq(&sp->queue_lock);
 }
 
 /*
@@ -403,7 +338,7 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 	head->func = func;
 	spin_lock_irqsave(&sp->queue_lock, flags);
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
-	rcu_batch_queue(&sp->batch_queue, head);
+	rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
 	if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) {
 		srcu_gp_start(sp);
 		queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
@@ -439,13 +374,13 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
 	if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) {
 		/* steal the processing owner */
+		rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
 		srcu_gp_start(sp);
-		rcu_batch_queue(&sp->batch_check0, head);
 		spin_unlock_irq(&sp->queue_lock);
 		/* give the processing owner to work_struct */
 		srcu_reschedule(sp, 0);
 	} else {
-		rcu_batch_queue(&sp->batch_queue, head);
+		rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
 		spin_unlock_irq(&sp->queue_lock);
 	}
 
@@ -543,19 +478,6 @@ EXPORT_SYMBOL_GPL(srcu_batches_completed);
 #define SRCU_INTERVAL		1
 
 /*
- * Move any new SRCU callbacks to the first stage of the SRCU grace
- * period pipeline.
- */
-static void srcu_collect_new(struct srcu_struct *sp)
-{
-	if (!rcu_batch_empty(&sp->batch_queue)) {
-		spin_lock_irq(&sp->queue_lock);
-		rcu_batch_move(&sp->batch_check0, &sp->batch_queue);
-		spin_unlock_irq(&sp->queue_lock);
-	}
-}
-
-/*
  * Core SRCU state machine.  Advance callbacks from ->batch_check0 to
  * ->batch_check1 and then to ->batch_done as readers drain.
  */
@@ -580,26 +502,7 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 		idx = 1 ^ (sp->completed & 1);
 		if (!try_check_zero(sp, idx, trycount))
 			return; /* readers present, retry after SRCU_INTERVAL */
-
-		/*
-		 * The callbacks in ->batch_check1 have already done
-		 * with their first zero check and flip back when they were
-		 * enqueued on ->batch_check0 in a previous invocation of
-		 * srcu_advance_batches().  (Presumably try_check_zero()
-		 * returned false during that invocation, leaving the
-		 * callbacks stranded on ->batch_check1.) They are therefore
-		 * ready to invoke, so move them to ->batch_done.
-		 */
-		rcu_batch_move(&sp->batch_done, &sp->batch_check1);
 		srcu_flip(sp);
-
-		/*
-		 * The callbacks in ->batch_check0 just finished their
-		 * first check zero and flip, so move them to ->batch_check1
-		 * for future checking on the other idx.
-		 */
-		rcu_batch_move(&sp->batch_check1, &sp->batch_check0);
-
 		WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN2);
 	}
 
@@ -613,14 +516,6 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 		trycount = trycount < 2 ? 2 : trycount;
 		if (!try_check_zero(sp, idx, trycount))
 			return; /* readers present, retry after SRCU_INTERVAL */
-
-		/*
-		 * The callbacks in ->batch_check1 have now waited for
-		 * all pre-existing readers using both idx values.  They are
-		 * therefore ready to invoke, so move them to ->batch_done.
-		 */
-		rcu_batch_move(&sp->batch_done, &sp->batch_check1);
-
 		srcu_gp_end(sp);
 	}
 }
@@ -633,17 +528,26 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
  */
 static void srcu_invoke_callbacks(struct srcu_struct *sp)
 {
-	int i;
-	struct rcu_head *head;
+	struct rcu_cblist ready_cbs;
+	struct rcu_head *rhp;
 
-	for (i = 0; i < SRCU_CALLBACK_BATCH; i++) {
-		head = rcu_batch_dequeue(&sp->batch_done);
-		if (!head)
-			break;
+	spin_lock_irq(&sp->queue_lock);
+	if (!rcu_segcblist_ready_cbs(&sp->srcu_cblist)) {
+		spin_unlock_irq(&sp->queue_lock);
+		return;
+	}
+	rcu_cblist_init(&ready_cbs);
+	rcu_segcblist_extract_done_cbs(&sp->srcu_cblist, &ready_cbs);
+	spin_unlock_irq(&sp->queue_lock);
+	rhp = rcu_cblist_dequeue(&ready_cbs);
+	for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
 		local_bh_disable();
-		head->func(head);
+		rhp->func(rhp);
 		local_bh_enable();
 	}
+	spin_lock_irq(&sp->queue_lock);
+	rcu_segcblist_insert_count(&sp->srcu_cblist, &ready_cbs);
+	spin_unlock_irq(&sp->queue_lock);
 }
 
 /*
@@ -654,9 +558,9 @@ static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
 {
 	bool pending = true;
 
-	if (rcu_all_batches_empty(sp)) {
+	if (rcu_segcblist_empty(&sp->srcu_cblist)) {
 		spin_lock_irq(&sp->queue_lock);
-		if (rcu_all_batches_empty(sp) &&
+		if (rcu_segcblist_empty(&sp->srcu_cblist) &&
 		    READ_ONCE(sp->srcu_state) == SRCU_STATE_DONE) {
 			WRITE_ONCE(sp->srcu_state, SRCU_STATE_IDLE);
 			pending = false;
@@ -677,7 +581,6 @@ void process_srcu(struct work_struct *work)
 
 	sp = container_of(work, struct srcu_struct, work.work);
 
-	srcu_collect_new(sp);
 	srcu_advance_batches(sp, 1);
 	srcu_invoke_callbacks(sp);
 	srcu_reschedule(sp, SRCU_INTERVAL);
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 93889ff21dbb..4f62651588ea 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -30,7 +30,7 @@
 #include <linux/seqlock.h>
 #include <linux/swait.h>
 #include <linux/stop_machine.h>
-#include "rcu_segcblist.h"
+#include <linux/rcu_segcblist.h>
 
 /*
  * Define shape of hierarchy based on NR_CPUS, CONFIG_RCU_FANOUT, and
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 27/40] srcu: Move combining-tree definitions for SRCU's benefit
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (25 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 26/40] srcu: Use rcu_segcblist to track SRCU callbacks Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 28/40] srcu: Move rcu_init_levelspread() to rcu_tree_node.h Paul E. McKenney
                   ` (13 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit moves the C preprocessor code that defines the default shape
of the rcu_node combining tree to a new include/linux/rcu_node_tree.h
file as a first step towards enabling SRCU to create its own combining
tree, which in turn enables SRCU to implement per-CPU callback handling,
thus avoiding contention on the lock currently guarding the single list
of callbacks.  Note that users of SRCU still need to know the size of
the srcu_struct structure, hence include/linux rather than kernel/rcu.

This commit is code-movement only.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcu_node_tree.h | 102 ++++++++++++++++++++++++++++++++++++++++++
 kernel/rcu/tree.h             |  71 +----------------------------
 2 files changed, 103 insertions(+), 70 deletions(-)
 create mode 100644 include/linux/rcu_node_tree.h

diff --git a/include/linux/rcu_node_tree.h b/include/linux/rcu_node_tree.h
new file mode 100644
index 000000000000..b7eb97096b1c
--- /dev/null
+++ b/include/linux/rcu_node_tree.h
@@ -0,0 +1,102 @@
+/*
+ * RCU node combining tree definitions.  These are used to compute
+ * global attributes while avoiding common-case global contention.  A key
+ * property that these computations rely on is a tournament-style approach
+ * where only one of the tasks contending a lower level in the tree need
+ * advance to the next higher level.  If properly configured, this allows
+ * unlimited scalability while maintaining a constant level of contention
+ * on the root node.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright IBM Corporation, 2017
+ *
+ * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ */
+
+#ifndef __LINUX_RCU_NODE_TREE_H
+#define __LINUX_RCU_NODE_TREE_H
+
+/*
+ * Define shape of hierarchy based on NR_CPUS, CONFIG_RCU_FANOUT, and
+ * CONFIG_RCU_FANOUT_LEAF.
+ * In theory, it should be possible to add more levels straightforwardly.
+ * In practice, this did work well going from three levels to four.
+ * Of course, your mileage may vary.
+ */
+
+#ifdef CONFIG_RCU_FANOUT
+#define RCU_FANOUT CONFIG_RCU_FANOUT
+#else /* #ifdef CONFIG_RCU_FANOUT */
+# ifdef CONFIG_64BIT
+# define RCU_FANOUT 64
+# else
+# define RCU_FANOUT 32
+# endif
+#endif /* #else #ifdef CONFIG_RCU_FANOUT */
+
+#ifdef CONFIG_RCU_FANOUT_LEAF
+#define RCU_FANOUT_LEAF CONFIG_RCU_FANOUT_LEAF
+#else /* #ifdef CONFIG_RCU_FANOUT_LEAF */
+#define RCU_FANOUT_LEAF 16
+#endif /* #else #ifdef CONFIG_RCU_FANOUT_LEAF */
+
+#define RCU_FANOUT_1	      (RCU_FANOUT_LEAF)
+#define RCU_FANOUT_2	      (RCU_FANOUT_1 * RCU_FANOUT)
+#define RCU_FANOUT_3	      (RCU_FANOUT_2 * RCU_FANOUT)
+#define RCU_FANOUT_4	      (RCU_FANOUT_3 * RCU_FANOUT)
+
+#if NR_CPUS <= RCU_FANOUT_1
+#  define RCU_NUM_LVLS	      1
+#  define NUM_RCU_LVL_0	      1
+#  define NUM_RCU_NODES	      NUM_RCU_LVL_0
+#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0 }
+#  define RCU_NODE_NAME_INIT  { "rcu_node_0" }
+#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0" }
+#elif NR_CPUS <= RCU_FANOUT_2
+#  define RCU_NUM_LVLS	      2
+#  define NUM_RCU_LVL_0	      1
+#  define NUM_RCU_LVL_1	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
+#  define NUM_RCU_NODES	      (NUM_RCU_LVL_0 + NUM_RCU_LVL_1)
+#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0, NUM_RCU_LVL_1 }
+#  define RCU_NODE_NAME_INIT  { "rcu_node_0", "rcu_node_1" }
+#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0", "rcu_node_fqs_1" }
+#elif NR_CPUS <= RCU_FANOUT_3
+#  define RCU_NUM_LVLS	      3
+#  define NUM_RCU_LVL_0	      1
+#  define NUM_RCU_LVL_1	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
+#  define NUM_RCU_LVL_2	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
+#  define NUM_RCU_NODES	      (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2)
+#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2 }
+#  define RCU_NODE_NAME_INIT  { "rcu_node_0", "rcu_node_1", "rcu_node_2" }
+#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2" }
+#elif NR_CPUS <= RCU_FANOUT_4
+#  define RCU_NUM_LVLS	      4
+#  define NUM_RCU_LVL_0	      1
+#  define NUM_RCU_LVL_1	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_3)
+#  define NUM_RCU_LVL_2	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
+#  define NUM_RCU_LVL_3	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
+#  define NUM_RCU_NODES	      (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3)
+#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2, NUM_RCU_LVL_3 }
+#  define RCU_NODE_NAME_INIT  { "rcu_node_0", "rcu_node_1", "rcu_node_2", "rcu_node_3" }
+#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2", "rcu_node_fqs_3" }
+#else
+# error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
+#endif /* #if (NR_CPUS) <= RCU_FANOUT_1 */
+
+extern int rcu_num_lvls;
+extern int rcu_num_nodes;
+
+#endif /* __LINUX_RCU_NODE_TREE_H */
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 4f62651588ea..1bec3958d44f 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -31,76 +31,7 @@
 #include <linux/swait.h>
 #include <linux/stop_machine.h>
 #include <linux/rcu_segcblist.h>
-
-/*
- * Define shape of hierarchy based on NR_CPUS, CONFIG_RCU_FANOUT, and
- * CONFIG_RCU_FANOUT_LEAF.
- * In theory, it should be possible to add more levels straightforwardly.
- * In practice, this did work well going from three levels to four.
- * Of course, your mileage may vary.
- */
-
-#ifdef CONFIG_RCU_FANOUT
-#define RCU_FANOUT CONFIG_RCU_FANOUT
-#else /* #ifdef CONFIG_RCU_FANOUT */
-# ifdef CONFIG_64BIT
-# define RCU_FANOUT 64
-# else
-# define RCU_FANOUT 32
-# endif
-#endif /* #else #ifdef CONFIG_RCU_FANOUT */
-
-#ifdef CONFIG_RCU_FANOUT_LEAF
-#define RCU_FANOUT_LEAF CONFIG_RCU_FANOUT_LEAF
-#else /* #ifdef CONFIG_RCU_FANOUT_LEAF */
-#define RCU_FANOUT_LEAF 16
-#endif /* #else #ifdef CONFIG_RCU_FANOUT_LEAF */
-
-#define RCU_FANOUT_1	      (RCU_FANOUT_LEAF)
-#define RCU_FANOUT_2	      (RCU_FANOUT_1 * RCU_FANOUT)
-#define RCU_FANOUT_3	      (RCU_FANOUT_2 * RCU_FANOUT)
-#define RCU_FANOUT_4	      (RCU_FANOUT_3 * RCU_FANOUT)
-
-#if NR_CPUS <= RCU_FANOUT_1
-#  define RCU_NUM_LVLS	      1
-#  define NUM_RCU_LVL_0	      1
-#  define NUM_RCU_NODES	      NUM_RCU_LVL_0
-#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0 }
-#  define RCU_NODE_NAME_INIT  { "rcu_node_0" }
-#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0" }
-#elif NR_CPUS <= RCU_FANOUT_2
-#  define RCU_NUM_LVLS	      2
-#  define NUM_RCU_LVL_0	      1
-#  define NUM_RCU_LVL_1	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
-#  define NUM_RCU_NODES	      (NUM_RCU_LVL_0 + NUM_RCU_LVL_1)
-#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0, NUM_RCU_LVL_1 }
-#  define RCU_NODE_NAME_INIT  { "rcu_node_0", "rcu_node_1" }
-#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0", "rcu_node_fqs_1" }
-#elif NR_CPUS <= RCU_FANOUT_3
-#  define RCU_NUM_LVLS	      3
-#  define NUM_RCU_LVL_0	      1
-#  define NUM_RCU_LVL_1	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
-#  define NUM_RCU_LVL_2	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
-#  define NUM_RCU_NODES	      (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2)
-#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2 }
-#  define RCU_NODE_NAME_INIT  { "rcu_node_0", "rcu_node_1", "rcu_node_2" }
-#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2" }
-#elif NR_CPUS <= RCU_FANOUT_4
-#  define RCU_NUM_LVLS	      4
-#  define NUM_RCU_LVL_0	      1
-#  define NUM_RCU_LVL_1	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_3)
-#  define NUM_RCU_LVL_2	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
-#  define NUM_RCU_LVL_3	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
-#  define NUM_RCU_NODES	      (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3)
-#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2, NUM_RCU_LVL_3 }
-#  define RCU_NODE_NAME_INIT  { "rcu_node_0", "rcu_node_1", "rcu_node_2", "rcu_node_3" }
-#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2", "rcu_node_fqs_3" }
-#else
-# error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
-#endif /* #if (NR_CPUS) <= RCU_FANOUT_1 */
-
-extern int rcu_num_lvls;
-extern int rcu_num_nodes;
+#include <linux/rcu_node_tree.h>
 
 /*
  * Dynticks per-CPU state.
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 28/40] srcu: Move rcu_init_levelspread() to rcu_tree_node.h
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (26 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 27/40] srcu: Move combining-tree definitions for SRCU's benefit Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 29/40] rcu: Remove redundant levelcnt[] array from rcu_init_one() Paul E. McKenney
                   ` (12 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit moves the rcu_init_levelspread() function from
kernel/rcu/tree.c to kernel/rcu/rcu.h so that SRCU can access it.  This is
another step towards enabling SRCU to create its own combining tree.
This commit is code-movement only, give or take knock-on adjustments.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcu_node_tree.h |  3 ---
 kernel/rcu/rcu.h              | 36 ++++++++++++++++++++++++++++++++++++
 kernel/rcu/srcu.c             |  1 +
 kernel/rcu/tree.c             | 25 -------------------------
 kernel/rcu/tree_trace.c       |  1 +
 5 files changed, 38 insertions(+), 28 deletions(-)

diff --git a/include/linux/rcu_node_tree.h b/include/linux/rcu_node_tree.h
index b7eb97096b1c..4b766b61e1a0 100644
--- a/include/linux/rcu_node_tree.h
+++ b/include/linux/rcu_node_tree.h
@@ -96,7 +96,4 @@
 # error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
 #endif /* #if (NR_CPUS) <= RCU_FANOUT_1 */
 
-extern int rcu_num_lvls;
-extern int rcu_num_nodes;
-
 #endif /* __LINUX_RCU_NODE_TREE_H */
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index a943b42a9cf7..87326479b39a 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -190,4 +190,40 @@ void rcu_test_sync_prims(void);
  */
 extern void resched_cpu(int cpu);
 
+#if defined(SRCU) || !defined(TINY_RCU)
+
+#include <linux/rcu_node_tree.h>
+
+extern int rcu_num_lvls;
+extern int rcu_num_nodes;
+static bool rcu_fanout_exact;
+static int rcu_fanout_leaf;
+
+/*
+ * Compute the per-level fanout, either using the exact fanout specified
+ * or balancing the tree, depending on the rcu_fanout_exact boot parameter.
+ */
+static inline void rcu_init_levelspread(int *levelspread, const int *levelcnt)
+{
+	int i;
+
+	if (rcu_fanout_exact) {
+		levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf;
+		for (i = rcu_num_lvls - 2; i >= 0; i--)
+			levelspread[i] = RCU_FANOUT;
+	} else {
+		int ccur;
+		int cprv;
+
+		cprv = nr_cpu_ids;
+		for (i = rcu_num_lvls - 1; i >= 0; i--) {
+			ccur = levelcnt[i];
+			levelspread[i] = (cprv + ccur - 1) / ccur;
+			cprv = ccur;
+		}
+	}
+}
+
+#endif /* #if defined(SRCU) || !defined(TINY_RCU) */
+
 #endif /* __LINUX_RCU_H */
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 132cd57c07f1..d51ab050f777 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -36,6 +36,7 @@
 #include <linux/delay.h>
 #include <linux/srcu.h>
 
+#include <linux/rcu_node_tree.h>
 #include "rcu.h"
 
 static int init_srcu_struct_fields(struct srcu_struct *sp)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f8b100902e21..c5a9674824ef 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3959,31 +3959,6 @@ void rcu_scheduler_starting(void)
 }
 
 /*
- * Compute the per-level fanout, either using the exact fanout specified
- * or balancing the tree, depending on the rcu_fanout_exact boot parameter.
- */
-static void __init rcu_init_levelspread(int *levelspread, const int *levelcnt)
-{
-	int i;
-
-	if (rcu_fanout_exact) {
-		levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf;
-		for (i = rcu_num_lvls - 2; i >= 0; i--)
-			levelspread[i] = RCU_FANOUT;
-	} else {
-		int ccur;
-		int cprv;
-
-		cprv = nr_cpu_ids;
-		for (i = rcu_num_lvls - 1; i >= 0; i--) {
-			ccur = levelcnt[i];
-			levelspread[i] = (cprv + ccur - 1) / ccur;
-			cprv = ccur;
-		}
-	}
-}
-
-/*
  * Helper function for rcu_init() that initializes one rcu_state structure.
  */
 static void __init rcu_init_one(struct rcu_state *rsp)
diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c
index 066c64071a7b..30c5bf89ee58 100644
--- a/kernel/rcu/tree_trace.c
+++ b/kernel/rcu/tree_trace.c
@@ -45,6 +45,7 @@
 
 #define RCU_TREE_NONCORE
 #include "tree.h"
+#include "rcu.h"
 
 static int r_open(struct inode *inode, struct file *file,
 					const struct seq_operations *op)
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 29/40] rcu: Remove redundant levelcnt[] array from rcu_init_one()
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (27 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 28/40] srcu: Move rcu_init_levelspread() to rcu_tree_node.h Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 30/40] srcu: Move rcu_node traversal macros to rcu.h Paul E. McKenney
                   ` (11 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The levelcnt[] array is identical to num_rcu_lvl[], so this commit
removes levelcnt[].

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index c5a9674824ef..101473f92ff5 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3968,7 +3968,6 @@ static void __init rcu_init_one(struct rcu_state *rsp)
 	static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
 	static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
 
-	int levelcnt[RCU_NUM_LVLS];		/* # nodes in each level. */
 	int levelspread[RCU_NUM_LVLS];		/* kids/node in each level. */
 	int cpustride = 1;
 	int i;
@@ -3983,18 +3982,16 @@ static void __init rcu_init_one(struct rcu_state *rsp)
 
 	/* Initialize the level-tracking arrays. */
 
-	for (i = 0; i < rcu_num_lvls; i++)
-		levelcnt[i] = num_rcu_lvl[i];
 	for (i = 1; i < rcu_num_lvls; i++)
-		rsp->level[i] = rsp->level[i - 1] + levelcnt[i - 1];
-	rcu_init_levelspread(levelspread, levelcnt);
+		rsp->level[i] = rsp->level[i - 1] + num_rcu_lvl[i - 1];
+	rcu_init_levelspread(levelspread, num_rcu_lvl);
 
 	/* Initialize the elements themselves, starting from the leaves. */
 
 	for (i = rcu_num_lvls - 1; i >= 0; i--) {
 		cpustride *= levelspread[i];
 		rnp = rsp->level[i];
-		for (j = 0; j < levelcnt[i]; j++, rnp++) {
+		for (j = 0; j < num_rcu_lvl[i]; j++, rnp++) {
 			raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
 			lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
 						   &rcu_node_class[i], buf[i]);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 30/40] srcu: Move rcu_node traversal macros to rcu.h
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (28 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 29/40] rcu: Remove redundant levelcnt[] array from rcu_init_one() Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 31/40] srcu: Make num_rcu_lvl[] array be external Paul E. McKenney
                   ` (10 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit moves rcu_for_each_node_breadth_first(),
rcu_for_each_nonleaf_node_breadth_first(), and
rcu_for_each_leaf_node() from kernel/rcu/tree.h to
kernel/rcu/rcu.h so that SRCU can access them.
This commit is code-movement only.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcu.h  | 35 +++++++++++++++++++++++++++++++++++
 kernel/rcu/tree.h | 35 -----------------------------------
 2 files changed, 35 insertions(+), 35 deletions(-)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 87326479b39a..5c1798ec32f7 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -224,6 +224,41 @@ static inline void rcu_init_levelspread(int *levelspread, const int *levelcnt)
 	}
 }
 
+/*
+ * Do a full breadth-first scan of the rcu_node structures for the
+ * specified rcu_state structure.
+ */
+#define rcu_for_each_node_breadth_first(rsp, rnp) \
+	for ((rnp) = &(rsp)->node[0]; \
+	     (rnp) < &(rsp)->node[rcu_num_nodes]; (rnp)++)
+
+/*
+ * Do a breadth-first scan of the non-leaf rcu_node structures for the
+ * specified rcu_state structure.  Note that if there is a singleton
+ * rcu_node tree with but one rcu_node structure, this loop is a no-op.
+ */
+#define rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) \
+	for ((rnp) = &(rsp)->node[0]; \
+	     (rnp) < (rsp)->level[rcu_num_lvls - 1]; (rnp)++)
+
+/*
+ * Scan the leaves of the rcu_node hierarchy for the specified rcu_state
+ * structure.  Note that if there is a singleton rcu_node tree with but
+ * one rcu_node structure, this loop -will- visit the rcu_node structure.
+ * It is still a leaf node, even if it is also the root node.
+ */
+#define rcu_for_each_leaf_node(rsp, rnp) \
+	for ((rnp) = (rsp)->level[rcu_num_lvls - 1]; \
+	     (rnp) < &(rsp)->node[rcu_num_nodes]; (rnp)++)
+
+/*
+ * Iterate over all possible CPUs in a leaf RCU node.
+ */
+#define for_each_leaf_node_possible_cpu(rnp, cpu) \
+	for ((cpu) = cpumask_next(rnp->grplo - 1, cpu_possible_mask); \
+	     cpu <= rnp->grphi; \
+	     cpu = cpumask_next((cpu), cpu_possible_mask))
+
 #endif /* #if defined(SRCU) || !defined(TINY_RCU) */
 
 #endif /* __LINUX_RCU_H */
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 1bec3958d44f..a2a45cb629d6 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -193,41 +193,6 @@ struct rcu_node {
 #define leaf_node_cpu_bit(rnp, cpu) (1UL << ((cpu) - (rnp)->grplo))
 
 /*
- * Do a full breadth-first scan of the rcu_node structures for the
- * specified rcu_state structure.
- */
-#define rcu_for_each_node_breadth_first(rsp, rnp) \
-	for ((rnp) = &(rsp)->node[0]; \
-	     (rnp) < &(rsp)->node[rcu_num_nodes]; (rnp)++)
-
-/*
- * Do a breadth-first scan of the non-leaf rcu_node structures for the
- * specified rcu_state structure.  Note that if there is a singleton
- * rcu_node tree with but one rcu_node structure, this loop is a no-op.
- */
-#define rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) \
-	for ((rnp) = &(rsp)->node[0]; \
-	     (rnp) < (rsp)->level[rcu_num_lvls - 1]; (rnp)++)
-
-/*
- * Scan the leaves of the rcu_node hierarchy for the specified rcu_state
- * structure.  Note that if there is a singleton rcu_node tree with but
- * one rcu_node structure, this loop -will- visit the rcu_node structure.
- * It is still a leaf node, even if it is also the root node.
- */
-#define rcu_for_each_leaf_node(rsp, rnp) \
-	for ((rnp) = (rsp)->level[rcu_num_lvls - 1]; \
-	     (rnp) < &(rsp)->node[rcu_num_nodes]; (rnp)++)
-
-/*
- * Iterate over all possible CPUs in a leaf RCU node.
- */
-#define for_each_leaf_node_possible_cpu(rnp, cpu) \
-	for ((cpu) = cpumask_next(rnp->grplo - 1, cpu_possible_mask); \
-	     cpu <= rnp->grphi; \
-	     cpu = cpumask_next((cpu), cpu_possible_mask))
-
-/*
  * Union to allow "aggregate OR" operation on the need for a quiescent
  * state by the normal and expedited grace periods.
  */
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 31/40] srcu: Make num_rcu_lvl[] array be external
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (29 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 30/40] srcu: Move rcu_node traversal macros to rcu.h Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 32/40] srcu: Fix bogus try_check_zero() comment Paul E. McKenney
                   ` (9 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit makes the num_rcu_lvl[] array external so that SRCU can
make use of it for initializing its upcoming srcu_node tree.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcu.h  | 1 +
 kernel/rcu/tree.c | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 5c1798ec32f7..4303b880ac99 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -195,6 +195,7 @@ extern void resched_cpu(int cpu);
 #include <linux/rcu_node_tree.h>
 
 extern int rcu_num_lvls;
+extern int num_rcu_lvl[];
 extern int rcu_num_nodes;
 static bool rcu_fanout_exact;
 static int rcu_fanout_leaf;
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 101473f92ff5..e0eb798181bc 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -123,7 +123,7 @@ static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
 module_param(rcu_fanout_leaf, int, 0444);
 int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
 /* Number of rcu_nodes at specified level. */
-static int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
+int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
 int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
 /* panic() on RCU Stall sysctl. */
 int sysctl_panic_on_rcu_stall __read_mostly;
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 32/40] srcu: Fix bogus try_check_zero() comment
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (30 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 31/40] srcu: Make num_rcu_lvl[] array be external Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 33/40] srcu: Improve rcu_seq grace-period-counter abstraction Paul E. McKenney
                   ` (8 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/srcu.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index d51ab050f777..5aeeaecfb673 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -254,10 +254,9 @@ static void srcu_gp_start(struct srcu_struct *sp)
 }
 
 /*
- * @@@ Wait until all pre-existing readers complete.  Such readers
- * will have used the index specified by "idx".
- * the caller should ensures the ->completed is not changed while checking
- * and idx = (->completed & 1) ^ 1
+ * Wait until all readers counted by array index idx complete, but loop
+ * a maximum of trycount times.  The caller must ensure that ->completed
+ * is not changed while checking.
  */
 static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
 {
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 33/40] srcu: Improve rcu_seq grace-period-counter abstraction
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (31 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 32/40] srcu: Fix bogus try_check_zero() comment Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 34/40] srcu: Allow a second bit in rcu_seq for SRCU state Paul E. McKenney
                   ` (7 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The expedited grace-period code contains several open-coded shifts
know the format of an rcu_seq grace-period counter, which is not
particularly good style.  This commit therefore creates a new
rcu_seq_ctr() function that extracts the counter portion of the
counter, and an rcu_seq_state() function that extracts the low-order
state bit.  This commit prepares for SRCU callback parallelization,
which will require two state bits.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcu.h      | 29 +++++++++++++++++++++++++----
 kernel/rcu/tree_exp.h |  9 ++++-----
 2 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 4303b880ac99..c62df93bfc1b 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -61,20 +61,41 @@
  * Grace-period counter management.
  */
 
+#define RCU_SEQ_CTR_SHIFT	1
+#define RCU_SEQ_STATE_MASK	((1 << RCU_SEQ_CTR_SHIFT) - 1)
+
+/*
+ * Return the counter portion of a sequence number previously returned
+ * by rcu_seq_snap() or rcu_seq_current().
+ */
+static inline unsigned long rcu_seq_ctr(unsigned long s)
+{
+	return s >> RCU_SEQ_CTR_SHIFT;
+}
+
+/*
+ * Return the state portion of a sequence number previously returned
+ * by rcu_seq_snap() or rcu_seq_current().
+ */
+static inline int rcu_seq_state(unsigned long s)
+{
+	return s & RCU_SEQ_STATE_MASK;
+}
+
 /* Adjust sequence number for start of update-side operation. */
 static inline void rcu_seq_start(unsigned long *sp)
 {
 	WRITE_ONCE(*sp, *sp + 1);
 	smp_mb(); /* Ensure update-side operation after counter increment. */
-	WARN_ON_ONCE(!(*sp & 0x1));
+	WARN_ON_ONCE(rcu_seq_state(*sp) != 1);
 }
 
 /* Adjust sequence number for end of update-side operation. */
 static inline void rcu_seq_end(unsigned long *sp)
 {
 	smp_mb(); /* Ensure update-side operation before counter increment. */
-	WARN_ON_ONCE(!(*sp & 0x1));
-	WRITE_ONCE(*sp, *sp + 1);
+	WARN_ON_ONCE(!rcu_seq_state(*sp));
+	WRITE_ONCE(*sp, (*sp | RCU_SEQ_STATE_MASK) + 1);
 }
 
 /* Take a snapshot of the update side's sequence number. */
@@ -82,7 +103,7 @@ static inline unsigned long rcu_seq_snap(unsigned long *sp)
 {
 	unsigned long s;
 
-	s = (READ_ONCE(*sp) + 3) & ~0x1;
+	s = (READ_ONCE(*sp) + 2 * RCU_SEQ_STATE_MASK + 1) & ~RCU_SEQ_STATE_MASK;
 	smp_mb(); /* Above access must not bleed into critical section. */
 	return s;
 }
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 027e123d93c7..e513b4ab1197 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -292,7 +292,7 @@ static bool exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
 			trace_rcu_exp_funnel_lock(rsp->name, rnp->level,
 						  rnp->grplo, rnp->grphi,
 						  TPS("wait"));
-			wait_event(rnp->exp_wq[(s >> 1) & 0x3],
+			wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
 				   sync_exp_work_done(rsp,
 						      &rdp->exp_workdone2, s));
 			return true;
@@ -534,7 +534,7 @@ static void rcu_exp_wait_wake(struct rcu_state *rsp, unsigned long s)
 			spin_unlock(&rnp->exp_lock);
 		}
 		smp_mb(); /* All above changes before wakeup. */
-		wake_up_all(&rnp->exp_wq[(rsp->expedited_sequence >> 1) & 0x3]);
+		wake_up_all(&rnp->exp_wq[rcu_seq_ctr(rsp->expedited_sequence) & 0x3]);
 	}
 	trace_rcu_exp_grace_period(rsp->name, s, TPS("endwake"));
 	mutex_unlock(&rsp->exp_wake_mutex);
@@ -612,9 +612,8 @@ static void _synchronize_rcu_expedited(struct rcu_state *rsp,
 	/* Wait for expedited grace period to complete. */
 	rdp = per_cpu_ptr(rsp->rda, raw_smp_processor_id());
 	rnp = rcu_get_root(rsp);
-	wait_event(rnp->exp_wq[(s >> 1) & 0x3],
-		   sync_exp_work_done(rsp,
-				      &rdp->exp_workdone0, s));
+	wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
+		   sync_exp_work_done(rsp, &rdp->exp_workdone0, s));
 	smp_mb(); /* Workqueue actions happen before return. */
 
 	/* Let the next expedited grace period start. */
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 34/40] srcu: Allow a second bit in rcu_seq for SRCU state
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (32 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 33/40] srcu: Improve rcu_seq grace-period-counter abstraction Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 35/40] srcu: Merge ->srcu_state into ->srcu_gp_seq Paul E. McKenney
                   ` (6 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit increases the number of reserved bits at the bottom of an
rcu_seq grace-period counter from one to two, as will be needed to
accommodate SRCU's three-state grace periods.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcu.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index c62df93bfc1b..87a0ac95b551 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -61,7 +61,7 @@
  * Grace-period counter management.
  */
 
-#define RCU_SEQ_CTR_SHIFT	1
+#define RCU_SEQ_CTR_SHIFT	2
 #define RCU_SEQ_STATE_MASK	((1 << RCU_SEQ_CTR_SHIFT) - 1)
 
 /*
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 35/40] srcu: Merge ->srcu_state into ->srcu_gp_seq
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (33 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 34/40] srcu: Allow a second bit in rcu_seq for SRCU state Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 36/40] srcu: Crude control of expedited grace periods Paul E. McKenney
                   ` (5 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

Updating ->srcu_state and ->srcu_gp_seq will lead to extremely complex
race conditions given multiple callback queues, so this commit takes
advantage of the two-bit state now available in rcu_seq counters to
store the state in the bottom two bits of ->srcu_gp_seq.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/srcu.h |  5 +----
 kernel/rcu/rcu.h     | 10 ++++++++++
 kernel/rcu/srcu.c    | 55 +++++++++++++++++++++++++++++++++-------------------
 3 files changed, 46 insertions(+), 24 deletions(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index ad154a7bc114..e7dbc01b61a1 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -43,8 +43,7 @@ struct srcu_struct {
 	unsigned long completed;
 	unsigned long srcu_gp_seq;
 	struct srcu_array __percpu *per_cpu_ref;
-	spinlock_t queue_lock; /* protect ->srcu_cblist, ->srcu_state */
-	int srcu_state;
+	spinlock_t queue_lock; /* protect ->srcu_cblist */
 	struct rcu_segcblist srcu_cblist;
 	struct delayed_work work;
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
@@ -56,7 +55,6 @@ struct srcu_struct {
 #define SRCU_STATE_IDLE		0
 #define SRCU_STATE_SCAN1	1
 #define SRCU_STATE_SCAN2	2
-#define SRCU_STATE_DONE		3
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
@@ -85,7 +83,6 @@ void process_srcu(struct work_struct *work);
 		.completed = -300,					\
 		.per_cpu_ref = &name##_srcu_array,			\
 		.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock),	\
-		.srcu_state = SRCU_STATE_IDLE,				\
 		.srcu_cblist = RCU_SEGCBLIST_INITIALIZER(name.srcu_cblist),\
 		.work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
 		__SRCU_DEP_MAP_INIT(name)				\
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 87a0ac95b551..73e16ec4054b 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -82,6 +82,16 @@ static inline int rcu_seq_state(unsigned long s)
 	return s & RCU_SEQ_STATE_MASK;
 }
 
+/*
+ * Set the state portion of the pointed-to sequence number.
+ * The caller is responsible for preventing conflicting updates.
+ */
+static inline void rcu_seq_set_state(unsigned long *sp, int newstate)
+{
+	WARN_ON_ONCE(newstate & ~RCU_SEQ_STATE_MASK);
+	WRITE_ONCE(*sp, (*sp & ~RCU_SEQ_STATE_MASK) + newstate);
+}
+
 /* Adjust sequence number for start of update-side operation. */
 static inline void rcu_seq_start(unsigned long *sp)
 {
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 5aeeaecfb673..97aec5d7b316 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -44,7 +44,6 @@ static int init_srcu_struct_fields(struct srcu_struct *sp)
 	sp->completed = 0;
 	sp->srcu_gp_seq = 0;
 	spin_lock_init(&sp->queue_lock);
-	sp->srcu_state = SRCU_STATE_IDLE;
 	rcu_segcblist_init(&sp->srcu_cblist);
 	INIT_DELAYED_WORK(&sp->work, process_srcu);
 	sp->per_cpu_ref = alloc_percpu(struct srcu_array);
@@ -180,6 +179,9 @@ static bool srcu_readers_active(struct srcu_struct *sp)
 	return sum;
 }
 
+#define SRCU_CALLBACK_BATCH	10
+#define SRCU_INTERVAL		1
+
 /**
  * cleanup_srcu_struct - deconstruct a sleep-RCU structure
  * @sp: structure to clean up.
@@ -194,8 +196,10 @@ void cleanup_srcu_struct(struct srcu_struct *sp)
 	if (WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist)))
 		return; /* Leakage unless caller handles error. */
 	flush_delayed_work(&sp->work);
-	if (WARN_ON(READ_ONCE(sp->srcu_state) != SRCU_STATE_IDLE))
+	if (WARN_ON(rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) != SRCU_STATE_IDLE)) {
+		pr_info("cleanup_srcu_struct: Active srcu_struct %lu CBs %c state: %d\n", rcu_segcblist_n_cbs(&sp->srcu_cblist), ".E"[rcu_segcblist_empty(&sp->srcu_cblist)], rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)));
 		return; /* Caller forgot to stop doing call_srcu()? */
+	}
 	free_percpu(sp->per_cpu_ref);
 	sp->per_cpu_ref = NULL;
 }
@@ -247,10 +251,13 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
  */
 static void srcu_gp_start(struct srcu_struct *sp)
 {
+	int state;
+
 	rcu_segcblist_accelerate(&sp->srcu_cblist,
 				 rcu_seq_snap(&sp->srcu_gp_seq));
-	WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
 	rcu_seq_start(&sp->srcu_gp_seq);
+	state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
+	WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
 }
 
 /*
@@ -294,7 +301,6 @@ static void srcu_flip(struct srcu_struct *sp)
 static void srcu_gp_end(struct srcu_struct *sp)
 {
 	rcu_seq_end(&sp->srcu_gp_seq);
-	WRITE_ONCE(sp->srcu_state, SRCU_STATE_DONE);
 
 	spin_lock_irq(&sp->queue_lock);
 	rcu_segcblist_advance(&sp->srcu_cblist,
@@ -339,7 +345,7 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 	spin_lock_irqsave(&sp->queue_lock, flags);
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
 	rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
-	if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) {
+	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
 		srcu_gp_start(sp);
 		queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
 	}
@@ -372,7 +378,7 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 	head->func = wakeme_after_rcu;
 	spin_lock_irq(&sp->queue_lock);
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
-	if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) {
+	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
 		/* steal the processing owner */
 		rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
 		srcu_gp_start(sp);
@@ -474,9 +480,6 @@ unsigned long srcu_batches_completed(struct srcu_struct *sp)
 }
 EXPORT_SYMBOL_GPL(srcu_batches_completed);
 
-#define SRCU_CALLBACK_BATCH	10
-#define SRCU_INTERVAL		1
-
 /*
  * Core SRCU state machine.  Advance callbacks from ->batch_check0 to
  * ->batch_check1 and then to ->batch_done as readers drain.
@@ -485,28 +488,40 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 {
 	int idx;
 
-	WARN_ON_ONCE(sp->srcu_state == SRCU_STATE_IDLE);
-
 	/*
 	 * Because readers might be delayed for an extended period after
 	 * fetching ->completed for their index, at any point in time there
 	 * might well be readers using both idx=0 and idx=1.  We therefore
 	 * need to wait for readers to clear from both index values before
 	 * invoking a callback.
+	 *
+	 * The load-acquire ensures that we see the accesses performed
+	 * by the prior grace period.
 	 */
+	idx = rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq)); /* ^^^ */
+	if (idx == SRCU_STATE_IDLE) {
+		spin_lock_irq(&sp->queue_lock);
+		if (rcu_segcblist_empty(&sp->srcu_cblist)) {
+			spin_unlock_irq(&sp->queue_lock);
+			return;
+		}
+		idx = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
+		if (idx == SRCU_STATE_IDLE)
+			srcu_gp_start(sp);
+		spin_unlock_irq(&sp->queue_lock);
+		if (idx != SRCU_STATE_IDLE)
+			return; /* Someone else started the grace period. */
+	}
 
-	if (sp->srcu_state == SRCU_STATE_DONE)
-		srcu_gp_start(sp);
-
-	if (sp->srcu_state == SRCU_STATE_SCAN1) {
+	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
 		idx = 1 ^ (sp->completed & 1);
 		if (!try_check_zero(sp, idx, trycount))
 			return; /* readers present, retry after SRCU_INTERVAL */
 		srcu_flip(sp);
-		WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN2);
+		rcu_seq_set_state(&sp->srcu_gp_seq, SRCU_STATE_SCAN2);
 	}
 
-	if (sp->srcu_state == SRCU_STATE_SCAN2) {
+	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN2) {
 
 		/*
 		 * SRCU read-side critical sections are normally short,
@@ -557,14 +572,14 @@ static void srcu_invoke_callbacks(struct srcu_struct *sp)
 static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
 {
 	bool pending = true;
+	int state;
 
 	if (rcu_segcblist_empty(&sp->srcu_cblist)) {
 		spin_lock_irq(&sp->queue_lock);
+		state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
 		if (rcu_segcblist_empty(&sp->srcu_cblist) &&
-		    READ_ONCE(sp->srcu_state) == SRCU_STATE_DONE) {
-			WRITE_ONCE(sp->srcu_state, SRCU_STATE_IDLE);
+		    state == SRCU_STATE_IDLE)
 			pending = false;
-		}
 		spin_unlock_irq(&sp->queue_lock);
 	}
 
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 36/40] srcu: Crude control of expedited grace periods
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (34 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 35/40] srcu: Merge ->srcu_state into ->srcu_gp_seq Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 37/40] srcu: Create a tiny SRCU Paul E. McKenney
                   ` (4 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

SRCU's implementation of expedited grace periods has always assumed
that the SRCU instance is idle when the expedited request arrives.
This commit improves this a bit by maintaining a count of the number
of outstanding expedited requests, thus allowing prior non-expedited
grace periods accommodate these requests by shifting to expedited mode.
However, any non-expedited wait already in progress will still wait for
the full duration.

Improved control of expedited grace periods is planned, but one step
at a time.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/srcu.h |  1 +
 kernel/rcu/srcu.c    | 84 ++++++++++++++++++++++++++++------------------------
 2 files changed, 47 insertions(+), 38 deletions(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index e7dbc01b61a1..73a1b6296224 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -42,6 +42,7 @@ struct srcu_array {
 struct srcu_struct {
 	unsigned long completed;
 	unsigned long srcu_gp_seq;
+	atomic_t srcu_exp_cnt;
 	struct srcu_array __percpu *per_cpu_ref;
 	spinlock_t queue_lock; /* protect ->srcu_cblist */
 	struct rcu_segcblist srcu_cblist;
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 97aec5d7b316..b62919be99e7 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -43,6 +43,7 @@ static int init_srcu_struct_fields(struct srcu_struct *sp)
 {
 	sp->completed = 0;
 	sp->srcu_gp_seq = 0;
+	atomic_set(&sp->srcu_exp_cnt, 0);
 	spin_lock_init(&sp->queue_lock);
 	rcu_segcblist_init(&sp->srcu_cblist);
 	INIT_DELAYED_WORK(&sp->work, process_srcu);
@@ -179,7 +180,6 @@ static bool srcu_readers_active(struct srcu_struct *sp)
 	return sum;
 }
 
-#define SRCU_CALLBACK_BATCH	10
 #define SRCU_INTERVAL		1
 
 /**
@@ -191,6 +191,7 @@ static bool srcu_readers_active(struct srcu_struct *sp)
  */
 void cleanup_srcu_struct(struct srcu_struct *sp)
 {
+	WARN_ON_ONCE(atomic_read(&sp->srcu_exp_cnt));
 	if (WARN_ON(srcu_readers_active(sp)))
 		return; /* Leakage unless caller handles error. */
 	if (WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist)))
@@ -238,13 +239,10 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
  * We use an adaptive strategy for synchronize_srcu() and especially for
  * synchronize_srcu_expedited().  We spin for a fixed time period
  * (defined below) to allow SRCU readers to exit their read-side critical
- * sections.  If there are still some readers after 10 microseconds,
- * we repeatedly block for 1-millisecond time periods.  This approach
- * has done well in testing, so there is no need for a config parameter.
+ * sections.  If there are still some readers after a few microseconds,
+ * we repeatedly block for 1-millisecond time periods.
  */
 #define SRCU_RETRY_CHECK_DELAY		5
-#define SYNCHRONIZE_SRCU_TRYCOUNT	2
-#define SYNCHRONIZE_SRCU_EXP_TRYCOUNT	12
 
 /*
  * Start an SRCU grace period.
@@ -261,16 +259,16 @@ static void srcu_gp_start(struct srcu_struct *sp)
 }
 
 /*
- * Wait until all readers counted by array index idx complete, but loop
- * a maximum of trycount times.  The caller must ensure that ->completed
- * is not changed while checking.
+ * Wait until all readers counted by array index idx complete, but
+ * loop an additional time if there is an expedited grace period pending.
+ * The caller must ensure that ->completed is not changed while checking.
  */
 static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
 {
 	for (;;) {
 		if (srcu_readers_active_idx_check(sp, idx))
 			return true;
-		if (--trycount <= 0)
+		if (--trycount + !!atomic_read(&sp->srcu_exp_cnt) <= 0)
 			return false;
 		udelay(SRCU_RETRY_CHECK_DELAY);
 	}
@@ -358,7 +356,7 @@ static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay);
 /*
  * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
  */
-static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
+static void __synchronize_srcu(struct srcu_struct *sp)
 {
 	struct rcu_synchronize rcu;
 	struct rcu_head *head = &rcu.head;
@@ -395,6 +393,32 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 }
 
 /**
+ * synchronize_srcu_expedited - Brute-force SRCU grace period
+ * @sp: srcu_struct with which to synchronize.
+ *
+ * Wait for an SRCU grace period to elapse, but be more aggressive about
+ * spinning rather than blocking when waiting.
+ *
+ * Note that synchronize_srcu_expedited() has the same deadlock and
+ * memory-ordering properties as does synchronize_srcu().
+ */
+void synchronize_srcu_expedited(struct srcu_struct *sp)
+{
+	bool do_norm = rcu_gp_is_normal();
+
+	if (!do_norm) {
+		atomic_inc(&sp->srcu_exp_cnt);
+		smp_mb__after_atomic(); /* increment before GP. */
+	}
+	__synchronize_srcu(sp);
+	if (!do_norm) {
+		smp_mb__before_atomic(); /* GP before decrement. */
+		atomic_dec(&sp->srcu_exp_cnt);
+	}
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
+
+/**
  * synchronize_srcu - wait for prior SRCU read-side critical-section completion
  * @sp: srcu_struct with which to synchronize.
  *
@@ -435,29 +459,14 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
  */
 void synchronize_srcu(struct srcu_struct *sp)
 {
-	__synchronize_srcu(sp, (rcu_gp_is_expedited() && !rcu_gp_is_normal())
-			   ? SYNCHRONIZE_SRCU_EXP_TRYCOUNT
-			   : SYNCHRONIZE_SRCU_TRYCOUNT);
+	if (rcu_gp_is_expedited())
+		synchronize_srcu_expedited(sp);
+	else
+		__synchronize_srcu(sp);
 }
 EXPORT_SYMBOL_GPL(synchronize_srcu);
 
 /**
- * synchronize_srcu_expedited - Brute-force SRCU grace period
- * @sp: srcu_struct with which to synchronize.
- *
- * Wait for an SRCU grace period to elapse, but be more aggressive about
- * spinning rather than blocking when waiting.
- *
- * Note that synchronize_srcu_expedited() has the same deadlock and
- * memory-ordering properties as does synchronize_srcu().
- */
-void synchronize_srcu_expedited(struct srcu_struct *sp)
-{
-	__synchronize_srcu(sp, SYNCHRONIZE_SRCU_EXP_TRYCOUNT);
-}
-EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
-
-/**
  * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
  * @sp: srcu_struct on which to wait for in-flight callbacks.
  */
@@ -484,7 +493,7 @@ EXPORT_SYMBOL_GPL(srcu_batches_completed);
  * Core SRCU state machine.  Advance callbacks from ->batch_check0 to
  * ->batch_check1 and then to ->batch_done as readers drain.
  */
-static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
+static void srcu_advance_batches(struct srcu_struct *sp)
 {
 	int idx;
 
@@ -515,8 +524,8 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 
 	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
 		idx = 1 ^ (sp->completed & 1);
-		if (!try_check_zero(sp, idx, trycount))
-			return; /* readers present, retry after SRCU_INTERVAL */
+		if (!try_check_zero(sp, idx, 1))
+			return; /* readers present, retry later. */
 		srcu_flip(sp);
 		rcu_seq_set_state(&sp->srcu_gp_seq, SRCU_STATE_SCAN2);
 	}
@@ -528,9 +537,8 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 		 * so check at least twice in quick succession after a flip.
 		 */
 		idx = 1 ^ (sp->completed & 1);
-		trycount = trycount < 2 ? 2 : trycount;
-		if (!try_check_zero(sp, idx, trycount))
-			return; /* readers present, retry after SRCU_INTERVAL */
+		if (!try_check_zero(sp, idx, 2))
+			return; /* readers present, retry after later. */
 		srcu_gp_end(sp);
 	}
 }
@@ -596,8 +604,8 @@ void process_srcu(struct work_struct *work)
 
 	sp = container_of(work, struct srcu_struct, work.work);
 
-	srcu_advance_batches(sp, 1);
+	srcu_advance_batches(sp);
 	srcu_invoke_callbacks(sp);
-	srcu_reschedule(sp, SRCU_INTERVAL);
+	srcu_reschedule(sp, atomic_read(&sp->srcu_exp_cnt) ? 0 : SRCU_INTERVAL);
 }
 EXPORT_SYMBOL_GPL(process_srcu);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 37/40] srcu: Create a tiny SRCU
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (35 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 36/40] srcu: Crude control of expedited grace periods Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-13  9:48   ` Peter Zijlstra
  2017-04-12 17:40 ` [PATCH tip/core/rcu 38/40] srcutorture: Print Tiny SRCU reader statistics Paul E. McKenney
                   ` (3 subsequent siblings)
  40 siblings, 1 reply; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

In response to automated complaints about modifications to SRCU
increasing its size, this commit creates a tiny SRCU that is
used in SMP=y && PREEMPT=n builds.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/srcu.h     |  69 ++-------------
 include/linux/srcutiny.h |  81 ++++++++++++++++++
 include/linux/srcutree.h |  91 ++++++++++++++++++++
 init/Kconfig             |  12 +++
 kernel/rcu/Makefile      |   3 +-
 kernel/rcu/rcutorture.c  |   2 +
 kernel/rcu/srcutiny.c    | 215 +++++++++++++++++++++++++++++++++++++++++++++++
 7 files changed, 411 insertions(+), 62 deletions(-)
 create mode 100644 include/linux/srcutiny.h
 create mode 100644 include/linux/srcutree.h
 create mode 100644 kernel/rcu/srcutiny.c

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 73a1b6296224..907f09b14eda 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -34,28 +34,7 @@
 #include <linux/workqueue.h>
 #include <linux/rcu_segcblist.h>
 
-struct srcu_array {
-	unsigned long lock_count[2];
-	unsigned long unlock_count[2];
-};
-
-struct srcu_struct {
-	unsigned long completed;
-	unsigned long srcu_gp_seq;
-	atomic_t srcu_exp_cnt;
-	struct srcu_array __percpu *per_cpu_ref;
-	spinlock_t queue_lock; /* protect ->srcu_cblist */
-	struct rcu_segcblist srcu_cblist;
-	struct delayed_work work;
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
-	struct lockdep_map dep_map;
-#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
-};
-
-/* Values for -> state variable. */
-#define SRCU_STATE_IDLE		0
-#define SRCU_STATE_SCAN1	1
-#define SRCU_STATE_SCAN2	2
+struct srcu_struct;
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
@@ -77,42 +56,13 @@ int init_srcu_struct(struct srcu_struct *sp);
 #define __SRCU_DEP_MAP_INIT(srcu_name)
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
-void process_srcu(struct work_struct *work);
-
-#define __SRCU_STRUCT_INIT(name)					\
-	{								\
-		.completed = -300,					\
-		.per_cpu_ref = &name##_srcu_array,			\
-		.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock),	\
-		.srcu_cblist = RCU_SEGCBLIST_INITIALIZER(name.srcu_cblist),\
-		.work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
-		__SRCU_DEP_MAP_INIT(name)				\
-	}
-
-/*
- * Define and initialize a srcu struct at build time.
- * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
- *
- * Note that although DEFINE_STATIC_SRCU() hides the name from other
- * files, the per-CPU variable rules nevertheless require that the
- * chosen name be globally unique.  These rules also prohibit use of
- * DEFINE_STATIC_SRCU() within a function.  If these rules are too
- * restrictive, declare the srcu_struct manually.  For example, in
- * each file:
- *
- *	static struct srcu_struct my_srcu;
- *
- * Then, before the first use of each my_srcu, manually initialize it:
- *
- *	init_srcu_struct(&my_srcu);
- *
- * See include/linux/percpu-defs.h for the rules on per-CPU variables.
- */
-#define __DEFINE_SRCU(name, is_static)					\
-	static DEFINE_PER_CPU(struct srcu_array, name##_srcu_array);\
-	is_static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
-#define DEFINE_SRCU(name)		__DEFINE_SRCU(name, /* not static */)
-#define DEFINE_STATIC_SRCU(name)	__DEFINE_SRCU(name, static)
+#ifdef CONFIG_TINY_SRCU
+#include <linux/srcutiny.h>
+#elif defined(CONFIG_TREE_SRCU)
+#include <linux/srcutree.h>
+#else
+#error "Unknown SRCU implementation specified to kernel configuration"
+#endif
 
 /**
  * call_srcu() - Queue a callback for invocation after an SRCU grace period
@@ -138,9 +88,6 @@ void cleanup_srcu_struct(struct srcu_struct *sp);
 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
 void synchronize_srcu(struct srcu_struct *sp);
-void synchronize_srcu_expedited(struct srcu_struct *sp);
-unsigned long srcu_batches_completed(struct srcu_struct *sp);
-void srcu_barrier(struct srcu_struct *sp);
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
new file mode 100644
index 000000000000..4f284e4f4d8c
--- /dev/null
+++ b/include/linux/srcutiny.h
@@ -0,0 +1,81 @@
+/*
+ * Sleepable Read-Copy Update mechanism for mutual exclusion,
+ *	tiny variant.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright (C) IBM Corporation, 2017
+ *
+ * Author: Paul McKenney <paulmck@us.ibm.com>
+ */
+
+#ifndef _LINUX_SRCU_TINY_H
+#define _LINUX_SRCU_TINY_H
+
+#include <linux/swait.h>
+
+struct srcu_struct {
+	int srcu_lock_nesting[2];	/* srcu_read_lock() nesting depth. */
+	struct swait_queue_head srcu_wq;
+					/* Last srcu_read_unlock() wakes GP. */
+	unsigned long srcu_gp_seq;	/* GP seq # for callback tagging. */
+	struct rcu_segcblist srcu_cblist;
+					/* Pending SRCU callbacks. */
+	int srcu_idx;			/* Current reader array element. */
+	bool srcu_gp_running;		/* GP workqueue running? */
+	bool srcu_gp_waiting;		/* GP waiting for readers? */
+	struct work_struct srcu_work;	/* For driving grace periods. */
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	struct lockdep_map dep_map;
+#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+};
+
+void srcu_drive_gp(struct work_struct *wp);
+
+#define __SRCU_STRUCT_INIT(name)					\
+{									\
+	.srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq),	\
+	.srcu_cblist = RCU_SEGCBLIST_INITIALIZER(name.srcu_cblist),	\
+	.srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp),	\
+	__SRCU_DEP_MAP_INIT(name)					\
+}
+
+/*
+ * This odd _STATIC_ arrangement is needed for API compatibility with
+ * Tree SRCU, which needs some per-CPU data.
+ */
+#define DEFINE_SRCU(name) \
+	struct srcu_struct name = __SRCU_STRUCT_INIT(name)
+#define DEFINE_STATIC_SRCU(name) \
+	static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
+
+void synchronize_srcu(struct srcu_struct *sp);
+
+static inline void synchronize_srcu_expedited(struct srcu_struct *sp)
+{
+	synchronize_srcu(sp);
+}
+
+static inline void srcu_barrier(struct srcu_struct *sp)
+{
+	synchronize_srcu(sp);
+}
+
+static inline unsigned long srcu_batches_completed(struct srcu_struct *sp)
+{
+	return 0;
+}
+
+#endif
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
new file mode 100644
index 000000000000..f2b3bd6c6bc2
--- /dev/null
+++ b/include/linux/srcutree.h
@@ -0,0 +1,91 @@
+/*
+ * Sleepable Read-Copy Update mechanism for mutual exclusion,
+ *	tree variant.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright (C) IBM Corporation, 2017
+ *
+ * Author: Paul McKenney <paulmck@us.ibm.com>
+ */
+
+#ifndef _LINUX_SRCU_TREE_H
+#define _LINUX_SRCU_TREE_H
+
+struct srcu_array {
+	unsigned long lock_count[2];
+	unsigned long unlock_count[2];
+};
+
+struct srcu_struct {
+	unsigned long completed;
+	unsigned long srcu_gp_seq;
+	atomic_t srcu_exp_cnt;
+	struct srcu_array __percpu *per_cpu_ref;
+	spinlock_t queue_lock; /* protect ->srcu_cblist */
+	struct rcu_segcblist srcu_cblist;
+	struct delayed_work work;
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	struct lockdep_map dep_map;
+#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+};
+
+/* Values for -> state variable. */
+#define SRCU_STATE_IDLE		0
+#define SRCU_STATE_SCAN1	1
+#define SRCU_STATE_SCAN2	2
+
+void process_srcu(struct work_struct *work);
+
+#define __SRCU_STRUCT_INIT(name)					\
+	{								\
+		.completed = -300,					\
+		.per_cpu_ref = &name##_srcu_array,			\
+		.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock),	\
+		.srcu_cblist = RCU_SEGCBLIST_INITIALIZER(name.srcu_cblist),\
+		.work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
+		__SRCU_DEP_MAP_INIT(name)				\
+	}
+
+/*
+ * Define and initialize a srcu struct at build time.
+ * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
+ *
+ * Note that although DEFINE_STATIC_SRCU() hides the name from other
+ * files, the per-CPU variable rules nevertheless require that the
+ * chosen name be globally unique.  These rules also prohibit use of
+ * DEFINE_STATIC_SRCU() within a function.  If these rules are too
+ * restrictive, declare the srcu_struct manually.  For example, in
+ * each file:
+ *
+ *	static struct srcu_struct my_srcu;
+ *
+ * Then, before the first use of each my_srcu, manually initialize it:
+ *
+ *	init_srcu_struct(&my_srcu);
+ *
+ * See include/linux/percpu-defs.h for the rules on per-CPU variables.
+ */
+#define __DEFINE_SRCU(name, is_static)					\
+	static DEFINE_PER_CPU(struct srcu_array, name##_srcu_array);\
+	is_static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
+#define DEFINE_SRCU(name)		__DEFINE_SRCU(name, /* not static */)
+#define DEFINE_STATIC_SRCU(name)	__DEFINE_SRCU(name, static)
+
+void synchronize_srcu_expedited(struct srcu_struct *sp);
+void srcu_barrier(struct srcu_struct *sp);
+unsigned long srcu_batches_completed(struct srcu_struct *sp);
+
+#endif
diff --git a/init/Kconfig b/init/Kconfig
index a92f27da4a27..d269f2ca17b8 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -526,6 +526,18 @@ config SRCU
 	  permits arbitrary sleeping or blocking within RCU read-side critical
 	  sections.
 
+config TINY_SRCU
+	bool
+	default y if TINY_RCU
+	help
+	  This option selects the single-CPU non-preemptible version of SRCU.
+
+config TREE_SRCU
+	bool
+	default y if !TINY_RCU
+	help
+	  This option selects the full-fledged version of SRCU.
+
 config TASKS_RCU
 	bool
 	default n
diff --git a/kernel/rcu/Makefile b/kernel/rcu/Makefile
index 18dfc485225c..b853214a2b99 100644
--- a/kernel/rcu/Makefile
+++ b/kernel/rcu/Makefile
@@ -3,7 +3,8 @@
 KCOV_INSTRUMENT := n
 
 obj-y += update.o sync.o
-obj-$(CONFIG_SRCU) += srcu.o
+obj-$(CONFIG_TREE_SRCU) += srcu.o
+obj-$(CONFIG_TINY_SRCU) += srcutiny.o
 obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
 obj-$(CONFIG_RCU_PERF_TEST) += rcuperf.o
 obj-$(CONFIG_TREE_RCU) += tree.o
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index cccc417a8135..98591e16db1a 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -559,6 +559,7 @@ static void srcu_torture_barrier(void)
 
 static void srcu_torture_stats(void)
 {
+#ifdef CONFIG_TREE_SRCU
 	int cpu;
 	int idx = srcu_ctlp->completed & 0x1;
 
@@ -587,6 +588,7 @@ static void srcu_torture_stats(void)
 		pr_cont(" %d(%ld,%ld)", cpu, c0, c1);
 	}
 	pr_cont("\n");
+#endif
 }
 
 static void srcu_torture_synchronize_expedited(void)
diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
new file mode 100644
index 000000000000..b8293527ee18
--- /dev/null
+++ b/kernel/rcu/srcutiny.c
@@ -0,0 +1,215 @@
+/*
+ * Sleepable Read-Copy Update mechanism for mutual exclusion,
+ *	tiny version for non-preemptible single-CPU use.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright (C) IBM Corporation, 2017
+ *
+ * Author: Paul McKenney <paulmck@us.ibm.com>
+ */
+
+#include <linux/export.h>
+#include <linux/mutex.h>
+#include <linux/preempt.h>
+#include <linux/rcupdate_wait.h>
+#include <linux/sched.h>
+#include <linux/delay.h>
+#include <linux/srcu.h>
+
+#include <linux/rcu_node_tree.h>
+#include "rcu.h"
+
+static int init_srcu_struct_fields(struct srcu_struct *sp)
+{
+	sp->srcu_lock_nesting[0] = 0;
+	sp->srcu_lock_nesting[1] = 0;
+	init_swait_queue_head(&sp->srcu_wq);
+	sp->srcu_gp_seq = 0;
+	rcu_segcblist_init(&sp->srcu_cblist);
+	sp->srcu_gp_running = false;
+	sp->srcu_gp_waiting = false;
+	sp->srcu_idx = 0;
+	INIT_WORK(&sp->srcu_work, srcu_drive_gp);
+	return 0;
+}
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+
+int __init_srcu_struct(struct srcu_struct *sp, const char *name,
+		       struct lock_class_key *key)
+{
+	/* Don't re-initialize a lock while it is held. */
+	debug_check_no_locks_freed((void *)sp, sizeof(*sp));
+	lockdep_init_map(&sp->dep_map, name, key, 0);
+	return init_srcu_struct_fields(sp);
+}
+EXPORT_SYMBOL_GPL(__init_srcu_struct);
+
+#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+/*
+ * init_srcu_struct - initialize a sleep-RCU structure
+ * @sp: structure to initialize.
+ *
+ * Must invoke this on a given srcu_struct before passing that srcu_struct
+ * to any other function.  Each srcu_struct represents a separate domain
+ * of SRCU protection.
+ */
+int init_srcu_struct(struct srcu_struct *sp)
+{
+	return init_srcu_struct_fields(sp);
+}
+EXPORT_SYMBOL_GPL(init_srcu_struct);
+
+#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+/*
+ * cleanup_srcu_struct - deconstruct a sleep-RCU structure
+ * @sp: structure to clean up.
+ *
+ * Must invoke this after you are finished using a given srcu_struct that
+ * was initialized via init_srcu_struct(), else you leak memory.
+ */
+void cleanup_srcu_struct(struct srcu_struct *sp)
+{
+	WARN_ON(sp->srcu_lock_nesting[0] || sp->srcu_lock_nesting[1]);
+	flush_work(&sp->srcu_work);
+	WARN_ON(rcu_seq_state(sp->srcu_gp_seq));
+	WARN_ON(sp->srcu_gp_running);
+	WARN_ON(sp->srcu_gp_waiting);
+	WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist));
+}
+EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
+
+/*
+ * Counts the new reader in the appropriate per-CPU element of the
+ * srcu_struct.  Must be called from process context.
+ * Returns an index that must be passed to the matching srcu_read_unlock().
+ */
+int __srcu_read_lock(struct srcu_struct *sp)
+{
+	int idx;
+
+	idx = READ_ONCE(sp->srcu_idx);
+	WRITE_ONCE(sp->srcu_lock_nesting[idx], sp->srcu_lock_nesting[idx] + 1);
+	return idx;
+}
+EXPORT_SYMBOL_GPL(__srcu_read_lock);
+
+/*
+ * Removes the count for the old reader from the appropriate element of
+ * the srcu_struct.  Must be called from process context.
+ */
+void __srcu_read_unlock(struct srcu_struct *sp, int idx)
+{
+	int newval = sp->srcu_lock_nesting[idx] - 1;
+
+	WRITE_ONCE(sp->srcu_lock_nesting[idx], newval);
+	if (!newval && READ_ONCE(sp->srcu_gp_waiting))
+		swake_up(&sp->srcu_wq);
+}
+EXPORT_SYMBOL_GPL(__srcu_read_unlock);
+
+/*
+ * Workqueue handler to drive one grace period and invoke any callbacks
+ * that become ready as a result.  Single-CPU and !PREEMPT operation
+ * means that we get away with murder on synchronization.  ;-)
+ */
+void srcu_drive_gp(struct work_struct *wp)
+{
+	int idx;
+	struct rcu_cblist ready_cbs;
+	struct srcu_struct *sp;
+	struct rcu_head *rhp;
+
+	sp = container_of(wp, struct srcu_struct, srcu_work);
+	if (sp->srcu_gp_running || rcu_segcblist_empty(&sp->srcu_cblist))
+		return; /* Already running or nothing to do. */
+
+	/* Tag recently arrived callbacks and wait for readers. */
+	WRITE_ONCE(sp->srcu_gp_running, true);
+	rcu_segcblist_accelerate(&sp->srcu_cblist,
+				 rcu_seq_snap(&sp->srcu_gp_seq));
+	rcu_seq_start(&sp->srcu_gp_seq);
+	idx = sp->srcu_idx;
+	WRITE_ONCE(sp->srcu_idx, !sp->srcu_idx);
+	WRITE_ONCE(sp->srcu_gp_waiting, true);  /* srcu_read_unlock() wakes! */
+	swait_event(sp->srcu_wq, !READ_ONCE(sp->srcu_lock_nesting[idx]));
+	WRITE_ONCE(sp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
+	rcu_seq_end(&sp->srcu_gp_seq);
+
+	/* Update callback list based on GP, and invoke ready callbacks. */
+	rcu_segcblist_advance(&sp->srcu_cblist,
+			      rcu_seq_current(&sp->srcu_gp_seq));
+	if (rcu_segcblist_ready_cbs(&sp->srcu_cblist)) {
+		rcu_cblist_init(&ready_cbs);
+		local_irq_disable();
+		rcu_segcblist_extract_done_cbs(&sp->srcu_cblist, &ready_cbs);
+		local_irq_enable();
+		rhp = rcu_cblist_dequeue(&ready_cbs);
+		for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
+			local_bh_disable();
+			rhp->func(rhp);
+			local_bh_enable();
+		}
+		local_irq_disable();
+		rcu_segcblist_insert_count(&sp->srcu_cblist, &ready_cbs);
+		local_irq_enable();
+	}
+	WRITE_ONCE(sp->srcu_gp_running, false);
+
+	/*
+	 * If more callbacks, reschedule ourselves.  This can race with
+	 * a call_srcu() at interrupt level, but the ->srcu_gp_running
+	 * checks will straighten that out.
+	 */
+	if (!rcu_segcblist_empty(&sp->srcu_cblist))
+		schedule_work(&sp->srcu_work);
+}
+EXPORT_SYMBOL_GPL(srcu_drive_gp);
+
+/*
+ * Enqueue an SRCU callback on the specified srcu_struct structure,
+ * initiating grace-period processing if it is not already running.
+ */
+void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
+	       rcu_callback_t func)
+{
+	unsigned long flags;
+
+	head->func = func;
+	local_irq_save(flags);
+	rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
+	local_irq_restore(flags);
+	if (!READ_ONCE(sp->srcu_gp_running))
+		schedule_work(&sp->srcu_work);
+}
+EXPORT_SYMBOL_GPL(call_srcu);
+
+/*
+ * synchronize_srcu - wait for prior SRCU read-side critical-section completion
+ */
+void synchronize_srcu(struct srcu_struct *sp)
+{
+	struct rcu_synchronize rs;
+
+	init_rcu_head_on_stack(&rs.head);
+	init_completion(&rs.completion);
+	call_srcu(sp, &rs.head, wakeme_after_rcu);
+	wait_for_completion(&rs.completion);
+	destroy_rcu_head_on_stack(&rs.head);
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 38/40] srcutorture: Print Tiny SRCU reader statistics
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (36 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 37/40] srcu: Create a tiny SRCU Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 39/40] srcu: Introduce CLASSIC_SRCU Kconfig option Paul E. McKenney
                   ` (2 subsequent siblings)
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The srcu_torture_stats() function is adapted to the specific srcu_struct
layout traditionally used by SRCU.  This commit therefore adds support
for Tiny SRCU.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcutorture.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 98591e16db1a..9cbb8a7b909d 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -559,11 +559,12 @@ static void srcu_torture_barrier(void)
 
 static void srcu_torture_stats(void)
 {
-#ifdef CONFIG_TREE_SRCU
-	int cpu;
-	int idx = srcu_ctlp->completed & 0x1;
+	int __maybe_unused cpu;
+	int idx;
 
-	pr_alert("%s%s per-CPU(idx=%d):",
+#ifdef CONFIG_TREE_SRCU
+	idx = srcu_ctlp->completed & 0x1;
+	pr_alert("%s%s Tree SRCU per-CPU(idx=%d):",
 		 torture_type, TORTURE_FLAG, idx);
 	for_each_possible_cpu(cpu) {
 		unsigned long l0, l1;
@@ -588,6 +589,12 @@ static void srcu_torture_stats(void)
 		pr_cont(" %d(%ld,%ld)", cpu, c0, c1);
 	}
 	pr_cont("\n");
+#elif defined(CONFIG_TINY_SRCU)
+	idx = READ_ONCE(srcu_ctlp->srcu_idx) & 0x1;
+	pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%d,%d)\n",
+		 torture_type, TORTURE_FLAG, idx,
+		 READ_ONCE(srcu_ctlp->srcu_lock_nesting[!idx]),
+		 READ_ONCE(srcu_ctlp->srcu_lock_nesting[idx]));
 #endif
 }
 
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 39/40] srcu: Introduce CLASSIC_SRCU Kconfig option
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (37 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 38/40] srcutorture: Print Tiny SRCU reader statistics Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-12 17:40 ` [PATCH tip/core/rcu 40/40] srcu: Parallelize callback handling Paul E. McKenney
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
  40 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The TREE_SRCU rewrite is large and a bit on the non-simple side, so
this commit helps reduce risk by allowing the old v4.11 SRCU algorithm
to be selected using a new CLASSIC_SRCU Kconfig option that depends
on RCU_EXPERT.  The default is to use the new TREE_SRCU and TINY_SRCU
algorithms, in order to help get these the testing that they need.
However, if your users do not require the update-side scalability that
is to be provided by TREE_SRCU, select RCU_EXPERT and then CLASSIC_SRCU
to revert back to the old classic SRCU algorithm.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/srcu.h        |   2 +
 include/linux/srcuclassic.h | 101 ++++++++
 init/Kconfig                |  21 +-
 kernel/rcu/Makefile         |   3 +-
 kernel/rcu/rcutorture.c     |   2 +-
 kernel/rcu/srcu.c           | 347 ++++++++++++++-----------
 kernel/rcu/srcutree.c       | 613 ++++++++++++++++++++++++++++++++++++++++++++
 7 files changed, 934 insertions(+), 155 deletions(-)
 create mode 100644 include/linux/srcuclassic.h
 create mode 100644 kernel/rcu/srcutree.c

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 907f09b14eda..167ad8831aaf 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -60,6 +60,8 @@ int init_srcu_struct(struct srcu_struct *sp);
 #include <linux/srcutiny.h>
 #elif defined(CONFIG_TREE_SRCU)
 #include <linux/srcutree.h>
+#elif defined(CONFIG_CLASSIC_SRCU)
+#include <linux/srcuclassic.h>
 #else
 #error "Unknown SRCU implementation specified to kernel configuration"
 #endif
diff --git a/include/linux/srcuclassic.h b/include/linux/srcuclassic.h
new file mode 100644
index 000000000000..41cf99930f34
--- /dev/null
+++ b/include/linux/srcuclassic.h
@@ -0,0 +1,101 @@
+/*
+ * Sleepable Read-Copy Update mechanism for mutual exclusion,
+ *	classic v4.11 variant.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright (C) IBM Corporation, 2017
+ *
+ * Author: Paul McKenney <paulmck@us.ibm.com>
+ */
+
+#ifndef _LINUX_SRCU_CLASSIC_H
+#define _LINUX_SRCU_CLASSIC_H
+
+struct srcu_array {
+	unsigned long lock_count[2];
+	unsigned long unlock_count[2];
+};
+
+struct rcu_batch {
+	struct rcu_head *head, **tail;
+};
+
+#define RCU_BATCH_INIT(name) { NULL, &(name.head) }
+
+struct srcu_struct {
+	unsigned long completed;
+	struct srcu_array __percpu *per_cpu_ref;
+	spinlock_t queue_lock; /* protect ->batch_queue, ->running */
+	bool running;
+	/* callbacks just queued */
+	struct rcu_batch batch_queue;
+	/* callbacks try to do the first check_zero */
+	struct rcu_batch batch_check0;
+	/* callbacks done with the first check_zero and the flip */
+	struct rcu_batch batch_check1;
+	struct rcu_batch batch_done;
+	struct delayed_work work;
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	struct lockdep_map dep_map;
+#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+};
+
+void process_srcu(struct work_struct *work);
+
+#define __SRCU_STRUCT_INIT(name)					\
+	{								\
+		.completed = -300,					\
+		.per_cpu_ref = &name##_srcu_array,			\
+		.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock),	\
+		.running = false,					\
+		.batch_queue = RCU_BATCH_INIT(name.batch_queue),	\
+		.batch_check0 = RCU_BATCH_INIT(name.batch_check0),	\
+		.batch_check1 = RCU_BATCH_INIT(name.batch_check1),	\
+		.batch_done = RCU_BATCH_INIT(name.batch_done),		\
+		.work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
+		__SRCU_DEP_MAP_INIT(name)				\
+	}
+
+/*
+ * Define and initialize a srcu struct at build time.
+ * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
+ *
+ * Note that although DEFINE_STATIC_SRCU() hides the name from other
+ * files, the per-CPU variable rules nevertheless require that the
+ * chosen name be globally unique.  These rules also prohibit use of
+ * DEFINE_STATIC_SRCU() within a function.  If these rules are too
+ * restrictive, declare the srcu_struct manually.  For example, in
+ * each file:
+ *
+ *	static struct srcu_struct my_srcu;
+ *
+ * Then, before the first use of each my_srcu, manually initialize it:
+ *
+ *	init_srcu_struct(&my_srcu);
+ *
+ * See include/linux/percpu-defs.h for the rules on per-CPU variables.
+ */
+#define __DEFINE_SRCU(name, is_static)					\
+	static DEFINE_PER_CPU(struct srcu_array, name##_srcu_array);\
+	is_static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
+#define DEFINE_SRCU(name)		__DEFINE_SRCU(name, /* not static */)
+#define DEFINE_STATIC_SRCU(name)	__DEFINE_SRCU(name, static)
+
+void synchronize_srcu_expedited(struct srcu_struct *sp);
+void srcu_barrier(struct srcu_struct *sp);
+unsigned long srcu_batches_completed(struct srcu_struct *sp);
+
+#endif
diff --git a/init/Kconfig b/init/Kconfig
index d269f2ca17b8..558cc3638ab9 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -526,15 +526,32 @@ config SRCU
 	  permits arbitrary sleeping or blocking within RCU read-side critical
 	  sections.
 
+config CLASSIC_SRCU
+	bool "Use v4.11 classic SRCU implementation"
+	default n
+	depends on RCU_EXPERT && SRCU
+	help
+	  This option selects the traditional well-tested classic SRCU
+	  implementation from v4.11, as might be desired for enterprise
+	  Linux distributions.  Without this option, the shiny new
+	  Tiny SRCU and Tree SRCU implementations are used instead.
+	  At some point, it is hoped that Tiny SRCU and Tree SRCU
+	  will accumulate enough test time and confidence to allow
+	  Classic SRCU to be dropped entirely.
+
+	  Say Y if you need a rock-solid SRCU.
+
+	  Say N if you would like help test Tree SRCU.
+
 config TINY_SRCU
 	bool
-	default y if TINY_RCU
+	default y if TINY_RCU && !CLASSIC_SRCU
 	help
 	  This option selects the single-CPU non-preemptible version of SRCU.
 
 config TREE_SRCU
 	bool
-	default y if !TINY_RCU
+	default y if !TINY_RCU && !CLASSIC_SRCU
 	help
 	  This option selects the full-fledged version of SRCU.
 
diff --git a/kernel/rcu/Makefile b/kernel/rcu/Makefile
index b853214a2b99..158e6593d58c 100644
--- a/kernel/rcu/Makefile
+++ b/kernel/rcu/Makefile
@@ -3,7 +3,8 @@
 KCOV_INSTRUMENT := n
 
 obj-y += update.o sync.o
-obj-$(CONFIG_TREE_SRCU) += srcu.o
+obj-$(CONFIG_CLASSIC_SRCU) += srcu.o
+obj-$(CONFIG_TREE_SRCU) += srcutree.o
 obj-$(CONFIG_TINY_SRCU) += srcutiny.o
 obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
 obj-$(CONFIG_RCU_PERF_TEST) += rcuperf.o
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 9cbb8a7b909d..6f344b6748a8 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -562,7 +562,7 @@ static void srcu_torture_stats(void)
 	int __maybe_unused cpu;
 	int idx;
 
-#ifdef CONFIG_TREE_SRCU
+#if defined(CONFIG_TREE_SRCU) || defined(CONFIG_CLASSIC_SRCU)
 	idx = srcu_ctlp->completed & 0x1;
 	pr_alert("%s%s Tree SRCU per-CPU(idx=%d):",
 		 torture_type, TORTURE_FLAG, idx);
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index b62919be99e7..1b11a7c3203e 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -36,16 +36,75 @@
 #include <linux/delay.h>
 #include <linux/srcu.h>
 
-#include <linux/rcu_node_tree.h>
 #include "rcu.h"
 
+/*
+ * Initialize an rcu_batch structure to empty.
+ */
+static inline void rcu_batch_init(struct rcu_batch *b)
+{
+	b->head = NULL;
+	b->tail = &b->head;
+}
+
+/*
+ * Enqueue a callback onto the tail of the specified rcu_batch structure.
+ */
+static inline void rcu_batch_queue(struct rcu_batch *b, struct rcu_head *head)
+{
+	*b->tail = head;
+	b->tail = &head->next;
+}
+
+/*
+ * Is the specified rcu_batch structure empty?
+ */
+static inline bool rcu_batch_empty(struct rcu_batch *b)
+{
+	return b->tail == &b->head;
+}
+
+/*
+ * Remove the callback at the head of the specified rcu_batch structure
+ * and return a pointer to it, or return NULL if the structure is empty.
+ */
+static inline struct rcu_head *rcu_batch_dequeue(struct rcu_batch *b)
+{
+	struct rcu_head *head;
+
+	if (rcu_batch_empty(b))
+		return NULL;
+
+	head = b->head;
+	b->head = head->next;
+	if (b->tail == &head->next)
+		rcu_batch_init(b);
+
+	return head;
+}
+
+/*
+ * Move all callbacks from the rcu_batch structure specified by "from" to
+ * the structure specified by "to".
+ */
+static inline void rcu_batch_move(struct rcu_batch *to, struct rcu_batch *from)
+{
+	if (!rcu_batch_empty(from)) {
+		*to->tail = from->head;
+		to->tail = from->tail;
+		rcu_batch_init(from);
+	}
+}
+
 static int init_srcu_struct_fields(struct srcu_struct *sp)
 {
 	sp->completed = 0;
-	sp->srcu_gp_seq = 0;
-	atomic_set(&sp->srcu_exp_cnt, 0);
 	spin_lock_init(&sp->queue_lock);
-	rcu_segcblist_init(&sp->srcu_cblist);
+	sp->running = false;
+	rcu_batch_init(&sp->batch_queue);
+	rcu_batch_init(&sp->batch_check0);
+	rcu_batch_init(&sp->batch_check1);
+	rcu_batch_init(&sp->batch_done);
 	INIT_DELAYED_WORK(&sp->work, process_srcu);
 	sp->per_cpu_ref = alloc_percpu(struct srcu_array);
 	return sp->per_cpu_ref ? 0 : -ENOMEM;
@@ -180,8 +239,6 @@ static bool srcu_readers_active(struct srcu_struct *sp)
 	return sum;
 }
 
-#define SRCU_INTERVAL		1
-
 /**
  * cleanup_srcu_struct - deconstruct a sleep-RCU structure
  * @sp: structure to clean up.
@@ -191,16 +248,8 @@ static bool srcu_readers_active(struct srcu_struct *sp)
  */
 void cleanup_srcu_struct(struct srcu_struct *sp)
 {
-	WARN_ON_ONCE(atomic_read(&sp->srcu_exp_cnt));
 	if (WARN_ON(srcu_readers_active(sp)))
 		return; /* Leakage unless caller handles error. */
-	if (WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist)))
-		return; /* Leakage unless caller handles error. */
-	flush_delayed_work(&sp->work);
-	if (WARN_ON(rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) != SRCU_STATE_IDLE)) {
-		pr_info("cleanup_srcu_struct: Active srcu_struct %lu CBs %c state: %d\n", rcu_segcblist_n_cbs(&sp->srcu_cblist), ".E"[rcu_segcblist_empty(&sp->srcu_cblist)], rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)));
-		return; /* Caller forgot to stop doing call_srcu()? */
-	}
 	free_percpu(sp->per_cpu_ref);
 	sp->per_cpu_ref = NULL;
 }
@@ -239,36 +288,26 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
  * We use an adaptive strategy for synchronize_srcu() and especially for
  * synchronize_srcu_expedited().  We spin for a fixed time period
  * (defined below) to allow SRCU readers to exit their read-side critical
- * sections.  If there are still some readers after a few microseconds,
- * we repeatedly block for 1-millisecond time periods.
+ * sections.  If there are still some readers after 10 microseconds,
+ * we repeatedly block for 1-millisecond time periods.  This approach
+ * has done well in testing, so there is no need for a config parameter.
  */
 #define SRCU_RETRY_CHECK_DELAY		5
+#define SYNCHRONIZE_SRCU_TRYCOUNT	2
+#define SYNCHRONIZE_SRCU_EXP_TRYCOUNT	12
 
 /*
- * Start an SRCU grace period.
- */
-static void srcu_gp_start(struct srcu_struct *sp)
-{
-	int state;
-
-	rcu_segcblist_accelerate(&sp->srcu_cblist,
-				 rcu_seq_snap(&sp->srcu_gp_seq));
-	rcu_seq_start(&sp->srcu_gp_seq);
-	state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
-	WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
-}
-
-/*
- * Wait until all readers counted by array index idx complete, but
- * loop an additional time if there is an expedited grace period pending.
- * The caller must ensure that ->completed is not changed while checking.
+ * @@@ Wait until all pre-existing readers complete.  Such readers
+ * will have used the index specified by "idx".
+ * the caller should ensures the ->completed is not changed while checking
+ * and idx = (->completed & 1) ^ 1
  */
 static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
 {
 	for (;;) {
 		if (srcu_readers_active_idx_check(sp, idx))
 			return true;
-		if (--trycount + !!atomic_read(&sp->srcu_exp_cnt) <= 0)
+		if (--trycount <= 0)
 			return false;
 		udelay(SRCU_RETRY_CHECK_DELAY);
 	}
@@ -294,19 +333,6 @@ static void srcu_flip(struct srcu_struct *sp)
 }
 
 /*
- * End an SRCU grace period.
- */
-static void srcu_gp_end(struct srcu_struct *sp)
-{
-	rcu_seq_end(&sp->srcu_gp_seq);
-
-	spin_lock_irq(&sp->queue_lock);
-	rcu_segcblist_advance(&sp->srcu_cblist,
-			      rcu_seq_current(&sp->srcu_gp_seq));
-	spin_unlock_irq(&sp->queue_lock);
-}
-
-/*
  * Enqueue an SRCU callback on the specified srcu_struct structure,
  * initiating grace-period processing if it is not already running.
  *
@@ -342,24 +368,26 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 	head->func = func;
 	spin_lock_irqsave(&sp->queue_lock, flags);
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
-	rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
-	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
-		srcu_gp_start(sp);
+	rcu_batch_queue(&sp->batch_queue, head);
+	if (!sp->running) {
+		sp->running = true;
 		queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
 	}
 	spin_unlock_irqrestore(&sp->queue_lock, flags);
 }
 EXPORT_SYMBOL_GPL(call_srcu);
 
-static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay);
+static void srcu_advance_batches(struct srcu_struct *sp, int trycount);
+static void srcu_reschedule(struct srcu_struct *sp);
 
 /*
  * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
  */
-static void __synchronize_srcu(struct srcu_struct *sp)
+static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 {
 	struct rcu_synchronize rcu;
 	struct rcu_head *head = &rcu.head;
+	bool done = false;
 
 	RCU_LOCKDEP_WARN(lock_is_held(&sp->dep_map) ||
 			 lock_is_held(&rcu_bh_lock_map) ||
@@ -367,8 +395,6 @@ static void __synchronize_srcu(struct srcu_struct *sp)
 			 lock_is_held(&rcu_sched_lock_map),
 			 "Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");
 
-	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
-		return;
 	might_sleep();
 	init_completion(&rcu.completion);
 
@@ -376,47 +402,31 @@ static void __synchronize_srcu(struct srcu_struct *sp)
 	head->func = wakeme_after_rcu;
 	spin_lock_irq(&sp->queue_lock);
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
-	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
+	if (!sp->running) {
 		/* steal the processing owner */
-		rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
-		srcu_gp_start(sp);
+		sp->running = true;
+		rcu_batch_queue(&sp->batch_check0, head);
 		spin_unlock_irq(&sp->queue_lock);
+
+		srcu_advance_batches(sp, trycount);
+		if (!rcu_batch_empty(&sp->batch_done)) {
+			BUG_ON(sp->batch_done.head != head);
+			rcu_batch_dequeue(&sp->batch_done);
+			done = true;
+		}
 		/* give the processing owner to work_struct */
-		srcu_reschedule(sp, 0);
+		srcu_reschedule(sp);
 	} else {
-		rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
+		rcu_batch_queue(&sp->batch_queue, head);
 		spin_unlock_irq(&sp->queue_lock);
 	}
 
-	wait_for_completion(&rcu.completion);
-	smp_mb(); /* Caller's later accesses after GP. */
-}
-
-/**
- * synchronize_srcu_expedited - Brute-force SRCU grace period
- * @sp: srcu_struct with which to synchronize.
- *
- * Wait for an SRCU grace period to elapse, but be more aggressive about
- * spinning rather than blocking when waiting.
- *
- * Note that synchronize_srcu_expedited() has the same deadlock and
- * memory-ordering properties as does synchronize_srcu().
- */
-void synchronize_srcu_expedited(struct srcu_struct *sp)
-{
-	bool do_norm = rcu_gp_is_normal();
-
-	if (!do_norm) {
-		atomic_inc(&sp->srcu_exp_cnt);
-		smp_mb__after_atomic(); /* increment before GP. */
-	}
-	__synchronize_srcu(sp);
-	if (!do_norm) {
-		smp_mb__before_atomic(); /* GP before decrement. */
-		atomic_dec(&sp->srcu_exp_cnt);
+	if (!done) {
+		wait_for_completion(&rcu.completion);
+		smp_mb(); /* Caller's later accesses after GP. */
 	}
+
 }
-EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
 
 /**
  * synchronize_srcu - wait for prior SRCU read-side critical-section completion
@@ -459,14 +469,29 @@ EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
  */
 void synchronize_srcu(struct srcu_struct *sp)
 {
-	if (rcu_gp_is_expedited())
-		synchronize_srcu_expedited(sp);
-	else
-		__synchronize_srcu(sp);
+	__synchronize_srcu(sp, (rcu_gp_is_expedited() && !rcu_gp_is_normal())
+			   ? SYNCHRONIZE_SRCU_EXP_TRYCOUNT
+			   : SYNCHRONIZE_SRCU_TRYCOUNT);
 }
 EXPORT_SYMBOL_GPL(synchronize_srcu);
 
 /**
+ * synchronize_srcu_expedited - Brute-force SRCU grace period
+ * @sp: srcu_struct with which to synchronize.
+ *
+ * Wait for an SRCU grace period to elapse, but be more aggressive about
+ * spinning rather than blocking when waiting.
+ *
+ * Note that synchronize_srcu_expedited() has the same deadlock and
+ * memory-ordering properties as does synchronize_srcu().
+ */
+void synchronize_srcu_expedited(struct srcu_struct *sp)
+{
+	__synchronize_srcu(sp, SYNCHRONIZE_SRCU_EXP_TRYCOUNT);
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
+
+/**
  * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
  * @sp: srcu_struct on which to wait for in-flight callbacks.
  */
@@ -489,13 +514,29 @@ unsigned long srcu_batches_completed(struct srcu_struct *sp)
 }
 EXPORT_SYMBOL_GPL(srcu_batches_completed);
 
+#define SRCU_CALLBACK_BATCH	10
+#define SRCU_INTERVAL		1
+
+/*
+ * Move any new SRCU callbacks to the first stage of the SRCU grace
+ * period pipeline.
+ */
+static void srcu_collect_new(struct srcu_struct *sp)
+{
+	if (!rcu_batch_empty(&sp->batch_queue)) {
+		spin_lock_irq(&sp->queue_lock);
+		rcu_batch_move(&sp->batch_check0, &sp->batch_queue);
+		spin_unlock_irq(&sp->queue_lock);
+	}
+}
+
 /*
  * Core SRCU state machine.  Advance callbacks from ->batch_check0 to
  * ->batch_check1 and then to ->batch_done as readers drain.
  */
-static void srcu_advance_batches(struct srcu_struct *sp)
+static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 {
-	int idx;
+	int idx = 1 ^ (sp->completed & 1);
 
 	/*
 	 * Because readers might be delayed for an extended period after
@@ -503,44 +544,50 @@ static void srcu_advance_batches(struct srcu_struct *sp)
 	 * might well be readers using both idx=0 and idx=1.  We therefore
 	 * need to wait for readers to clear from both index values before
 	 * invoking a callback.
-	 *
-	 * The load-acquire ensures that we see the accesses performed
-	 * by the prior grace period.
 	 */
-	idx = rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq)); /* ^^^ */
-	if (idx == SRCU_STATE_IDLE) {
-		spin_lock_irq(&sp->queue_lock);
-		if (rcu_segcblist_empty(&sp->srcu_cblist)) {
-			spin_unlock_irq(&sp->queue_lock);
-			return;
-		}
-		idx = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
-		if (idx == SRCU_STATE_IDLE)
-			srcu_gp_start(sp);
-		spin_unlock_irq(&sp->queue_lock);
-		if (idx != SRCU_STATE_IDLE)
-			return; /* Someone else started the grace period. */
-	}
 
-	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
-		idx = 1 ^ (sp->completed & 1);
-		if (!try_check_zero(sp, idx, 1))
-			return; /* readers present, retry later. */
-		srcu_flip(sp);
-		rcu_seq_set_state(&sp->srcu_gp_seq, SRCU_STATE_SCAN2);
-	}
+	if (rcu_batch_empty(&sp->batch_check0) &&
+	    rcu_batch_empty(&sp->batch_check1))
+		return; /* no callbacks need to be advanced */
 
-	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN2) {
+	if (!try_check_zero(sp, idx, trycount))
+		return; /* failed to advance, will try after SRCU_INTERVAL */
 
-		/*
-		 * SRCU read-side critical sections are normally short,
-		 * so check at least twice in quick succession after a flip.
-		 */
-		idx = 1 ^ (sp->completed & 1);
-		if (!try_check_zero(sp, idx, 2))
-			return; /* readers present, retry after later. */
-		srcu_gp_end(sp);
-	}
+	/*
+	 * The callbacks in ->batch_check1 have already done with their
+	 * first zero check and flip back when they were enqueued on
+	 * ->batch_check0 in a previous invocation of srcu_advance_batches().
+	 * (Presumably try_check_zero() returned false during that
+	 * invocation, leaving the callbacks stranded on ->batch_check1.)
+	 * They are therefore ready to invoke, so move them to ->batch_done.
+	 */
+	rcu_batch_move(&sp->batch_done, &sp->batch_check1);
+
+	if (rcu_batch_empty(&sp->batch_check0))
+		return; /* no callbacks need to be advanced */
+	srcu_flip(sp);
+
+	/*
+	 * The callbacks in ->batch_check0 just finished their
+	 * first check zero and flip, so move them to ->batch_check1
+	 * for future checking on the other idx.
+	 */
+	rcu_batch_move(&sp->batch_check1, &sp->batch_check0);
+
+	/*
+	 * SRCU read-side critical sections are normally short, so check
+	 * at least twice in quick succession after a flip.
+	 */
+	trycount = trycount < 2 ? 2 : trycount;
+	if (!try_check_zero(sp, idx^1, trycount))
+		return; /* failed to advance, will try after SRCU_INTERVAL */
+
+	/*
+	 * The callbacks in ->batch_check1 have now waited for all
+	 * pre-existing readers using both idx values.  They are therefore
+	 * ready to invoke, so move them to ->batch_done.
+	 */
+	rcu_batch_move(&sp->batch_done, &sp->batch_check1);
 }
 
 /*
@@ -551,48 +598,45 @@ static void srcu_advance_batches(struct srcu_struct *sp)
  */
 static void srcu_invoke_callbacks(struct srcu_struct *sp)
 {
-	struct rcu_cblist ready_cbs;
-	struct rcu_head *rhp;
+	int i;
+	struct rcu_head *head;
 
-	spin_lock_irq(&sp->queue_lock);
-	if (!rcu_segcblist_ready_cbs(&sp->srcu_cblist)) {
-		spin_unlock_irq(&sp->queue_lock);
-		return;
-	}
-	rcu_cblist_init(&ready_cbs);
-	rcu_segcblist_extract_done_cbs(&sp->srcu_cblist, &ready_cbs);
-	spin_unlock_irq(&sp->queue_lock);
-	rhp = rcu_cblist_dequeue(&ready_cbs);
-	for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
+	for (i = 0; i < SRCU_CALLBACK_BATCH; i++) {
+		head = rcu_batch_dequeue(&sp->batch_done);
+		if (!head)
+			break;
 		local_bh_disable();
-		rhp->func(rhp);
+		head->func(head);
 		local_bh_enable();
 	}
-	spin_lock_irq(&sp->queue_lock);
-	rcu_segcblist_insert_count(&sp->srcu_cblist, &ready_cbs);
-	spin_unlock_irq(&sp->queue_lock);
 }
 
 /*
  * Finished one round of SRCU grace period.  Start another if there are
  * more SRCU callbacks queued, otherwise put SRCU into not-running state.
  */
-static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
+static void srcu_reschedule(struct srcu_struct *sp)
 {
 	bool pending = true;
-	int state;
 
-	if (rcu_segcblist_empty(&sp->srcu_cblist)) {
+	if (rcu_batch_empty(&sp->batch_done) &&
+	    rcu_batch_empty(&sp->batch_check1) &&
+	    rcu_batch_empty(&sp->batch_check0) &&
+	    rcu_batch_empty(&sp->batch_queue)) {
 		spin_lock_irq(&sp->queue_lock);
-		state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
-		if (rcu_segcblist_empty(&sp->srcu_cblist) &&
-		    state == SRCU_STATE_IDLE)
+		if (rcu_batch_empty(&sp->batch_done) &&
+		    rcu_batch_empty(&sp->batch_check1) &&
+		    rcu_batch_empty(&sp->batch_check0) &&
+		    rcu_batch_empty(&sp->batch_queue)) {
+			sp->running = false;
 			pending = false;
+		}
 		spin_unlock_irq(&sp->queue_lock);
 	}
 
 	if (pending)
-		queue_delayed_work(system_power_efficient_wq, &sp->work, delay);
+		queue_delayed_work(system_power_efficient_wq,
+				   &sp->work, SRCU_INTERVAL);
 }
 
 /*
@@ -604,8 +648,9 @@ void process_srcu(struct work_struct *work)
 
 	sp = container_of(work, struct srcu_struct, work.work);
 
-	srcu_advance_batches(sp);
+	srcu_collect_new(sp);
+	srcu_advance_batches(sp, 1);
 	srcu_invoke_callbacks(sp);
-	srcu_reschedule(sp, atomic_read(&sp->srcu_exp_cnt) ? 0 : SRCU_INTERVAL);
+	srcu_reschedule(sp);
 }
 EXPORT_SYMBOL_GPL(process_srcu);
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
new file mode 100644
index 000000000000..da676b0d016b
--- /dev/null
+++ b/kernel/rcu/srcutree.c
@@ -0,0 +1,613 @@
+/*
+ * Sleepable Read-Copy Update mechanism for mutual exclusion.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright (C) IBM Corporation, 2006
+ * Copyright (C) Fujitsu, 2012
+ *
+ * Author: Paul McKenney <paulmck@us.ibm.com>
+ *	   Lai Jiangshan <laijs@cn.fujitsu.com>
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ *		Documentation/RCU/ *.txt
+ *
+ */
+
+#include <linux/export.h>
+#include <linux/mutex.h>
+#include <linux/percpu.h>
+#include <linux/preempt.h>
+#include <linux/rcupdate_wait.h>
+#include <linux/sched.h>
+#include <linux/smp.h>
+#include <linux/delay.h>
+#include <linux/srcu.h>
+
+#include <linux/rcu_node_tree.h>
+#include "rcu.h"
+
+static int init_srcu_struct_fields(struct srcu_struct *sp)
+{
+	sp->completed = 0;
+	sp->srcu_gp_seq = 0;
+	atomic_set(&sp->srcu_exp_cnt, 0);
+	spin_lock_init(&sp->queue_lock);
+	rcu_segcblist_init(&sp->srcu_cblist);
+	INIT_DELAYED_WORK(&sp->work, process_srcu);
+	sp->per_cpu_ref = alloc_percpu(struct srcu_array);
+	return sp->per_cpu_ref ? 0 : -ENOMEM;
+}
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+
+int __init_srcu_struct(struct srcu_struct *sp, const char *name,
+		       struct lock_class_key *key)
+{
+	/* Don't re-initialize a lock while it is held. */
+	debug_check_no_locks_freed((void *)sp, sizeof(*sp));
+	lockdep_init_map(&sp->dep_map, name, key, 0);
+	return init_srcu_struct_fields(sp);
+}
+EXPORT_SYMBOL_GPL(__init_srcu_struct);
+
+#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+/**
+ * init_srcu_struct - initialize a sleep-RCU structure
+ * @sp: structure to initialize.
+ *
+ * Must invoke this on a given srcu_struct before passing that srcu_struct
+ * to any other function.  Each srcu_struct represents a separate domain
+ * of SRCU protection.
+ */
+int init_srcu_struct(struct srcu_struct *sp)
+{
+	return init_srcu_struct_fields(sp);
+}
+EXPORT_SYMBOL_GPL(init_srcu_struct);
+
+#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+/*
+ * Returns approximate total of the readers' ->lock_count[] values for the
+ * rank of per-CPU counters specified by idx.
+ */
+static unsigned long srcu_readers_lock_idx(struct srcu_struct *sp, int idx)
+{
+	int cpu;
+	unsigned long sum = 0;
+
+	for_each_possible_cpu(cpu) {
+		struct srcu_array *cpuc = per_cpu_ptr(sp->per_cpu_ref, cpu);
+
+		sum += READ_ONCE(cpuc->lock_count[idx]);
+	}
+	return sum;
+}
+
+/*
+ * Returns approximate total of the readers' ->unlock_count[] values for the
+ * rank of per-CPU counters specified by idx.
+ */
+static unsigned long srcu_readers_unlock_idx(struct srcu_struct *sp, int idx)
+{
+	int cpu;
+	unsigned long sum = 0;
+
+	for_each_possible_cpu(cpu) {
+		struct srcu_array *cpuc = per_cpu_ptr(sp->per_cpu_ref, cpu);
+
+		sum += READ_ONCE(cpuc->unlock_count[idx]);
+	}
+	return sum;
+}
+
+/*
+ * Return true if the number of pre-existing readers is determined to
+ * be zero.
+ */
+static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx)
+{
+	unsigned long unlocks;
+
+	unlocks = srcu_readers_unlock_idx(sp, idx);
+
+	/*
+	 * Make sure that a lock is always counted if the corresponding
+	 * unlock is counted. Needs to be a smp_mb() as the read side may
+	 * contain a read from a variable that is written to before the
+	 * synchronize_srcu() in the write side. In this case smp_mb()s
+	 * A and B act like the store buffering pattern.
+	 *
+	 * This smp_mb() also pairs with smp_mb() C to prevent accesses
+	 * after the synchronize_srcu() from being executed before the
+	 * grace period ends.
+	 */
+	smp_mb(); /* A */
+
+	/*
+	 * If the locks are the same as the unlocks, then there must have
+	 * been no readers on this index at some time in between. This does
+	 * not mean that there are no more readers, as one could have read
+	 * the current index but not have incremented the lock counter yet.
+	 *
+	 * Possible bug: There is no guarantee that there haven't been
+	 * ULONG_MAX increments of ->lock_count[] since the unlocks were
+	 * counted, meaning that this could return true even if there are
+	 * still active readers.  Since there are no memory barriers around
+	 * srcu_flip(), the CPU is not required to increment ->completed
+	 * before running srcu_readers_unlock_idx(), which means that there
+	 * could be an arbitrarily large number of critical sections that
+	 * execute after srcu_readers_unlock_idx() but use the old value
+	 * of ->completed.
+	 */
+	return srcu_readers_lock_idx(sp, idx) == unlocks;
+}
+
+/**
+ * srcu_readers_active - returns true if there are readers. and false
+ *                       otherwise
+ * @sp: which srcu_struct to count active readers (holding srcu_read_lock).
+ *
+ * Note that this is not an atomic primitive, and can therefore suffer
+ * severe errors when invoked on an active srcu_struct.  That said, it
+ * can be useful as an error check at cleanup time.
+ */
+static bool srcu_readers_active(struct srcu_struct *sp)
+{
+	int cpu;
+	unsigned long sum = 0;
+
+	for_each_possible_cpu(cpu) {
+		struct srcu_array *cpuc = per_cpu_ptr(sp->per_cpu_ref, cpu);
+
+		sum += READ_ONCE(cpuc->lock_count[0]);
+		sum += READ_ONCE(cpuc->lock_count[1]);
+		sum -= READ_ONCE(cpuc->unlock_count[0]);
+		sum -= READ_ONCE(cpuc->unlock_count[1]);
+	}
+	return sum;
+}
+
+#define SRCU_INTERVAL		1
+
+/**
+ * cleanup_srcu_struct - deconstruct a sleep-RCU structure
+ * @sp: structure to clean up.
+ *
+ * Must invoke this after you are finished using a given srcu_struct that
+ * was initialized via init_srcu_struct(), else you leak memory.
+ */
+void cleanup_srcu_struct(struct srcu_struct *sp)
+{
+	WARN_ON_ONCE(atomic_read(&sp->srcu_exp_cnt));
+	if (WARN_ON(srcu_readers_active(sp)))
+		return; /* Leakage unless caller handles error. */
+	if (WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist)))
+		return; /* Leakage unless caller handles error. */
+	flush_delayed_work(&sp->work);
+	if (WARN_ON(rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) != SRCU_STATE_IDLE)) {
+		pr_info("cleanup_srcu_struct: Active srcu_struct %lu CBs %c state: %d\n", rcu_segcblist_n_cbs(&sp->srcu_cblist), ".E"[rcu_segcblist_empty(&sp->srcu_cblist)], rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)));
+		return; /* Caller forgot to stop doing call_srcu()? */
+	}
+	free_percpu(sp->per_cpu_ref);
+	sp->per_cpu_ref = NULL;
+}
+EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
+
+/*
+ * Counts the new reader in the appropriate per-CPU element of the
+ * srcu_struct.  Must be called from process context.
+ * Returns an index that must be passed to the matching srcu_read_unlock().
+ */
+int __srcu_read_lock(struct srcu_struct *sp)
+{
+	int idx;
+
+	idx = READ_ONCE(sp->completed) & 0x1;
+	__this_cpu_inc(sp->per_cpu_ref->lock_count[idx]);
+	smp_mb(); /* B */  /* Avoid leaking the critical section. */
+	return idx;
+}
+EXPORT_SYMBOL_GPL(__srcu_read_lock);
+
+/*
+ * Removes the count for the old reader from the appropriate per-CPU
+ * element of the srcu_struct.  Note that this may well be a different
+ * CPU than that which was incremented by the corresponding srcu_read_lock().
+ * Must be called from process context.
+ */
+void __srcu_read_unlock(struct srcu_struct *sp, int idx)
+{
+	smp_mb(); /* C */  /* Avoid leaking the critical section. */
+	this_cpu_inc(sp->per_cpu_ref->unlock_count[idx]);
+}
+EXPORT_SYMBOL_GPL(__srcu_read_unlock);
+
+/*
+ * We use an adaptive strategy for synchronize_srcu() and especially for
+ * synchronize_srcu_expedited().  We spin for a fixed time period
+ * (defined below) to allow SRCU readers to exit their read-side critical
+ * sections.  If there are still some readers after a few microseconds,
+ * we repeatedly block for 1-millisecond time periods.
+ */
+#define SRCU_RETRY_CHECK_DELAY		5
+
+/*
+ * Start an SRCU grace period.
+ */
+static void srcu_gp_start(struct srcu_struct *sp)
+{
+	int state;
+
+	rcu_segcblist_accelerate(&sp->srcu_cblist,
+				 rcu_seq_snap(&sp->srcu_gp_seq));
+	rcu_seq_start(&sp->srcu_gp_seq);
+	state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
+	WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
+}
+
+/*
+ * Wait until all readers counted by array index idx complete, but
+ * loop an additional time if there is an expedited grace period pending.
+ * The caller must ensure that ->completed is not changed while checking.
+ */
+static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
+{
+	for (;;) {
+		if (srcu_readers_active_idx_check(sp, idx))
+			return true;
+		if (--trycount + !!atomic_read(&sp->srcu_exp_cnt) <= 0)
+			return false;
+		udelay(SRCU_RETRY_CHECK_DELAY);
+	}
+}
+
+/*
+ * Increment the ->completed counter so that future SRCU readers will
+ * use the other rank of the ->(un)lock_count[] arrays.  This allows
+ * us to wait for pre-existing readers in a starvation-free manner.
+ */
+static void srcu_flip(struct srcu_struct *sp)
+{
+	WRITE_ONCE(sp->completed, sp->completed + 1);
+
+	/*
+	 * Ensure that if the updater misses an __srcu_read_unlock()
+	 * increment, that task's next __srcu_read_lock() will see the
+	 * above counter update.  Note that both this memory barrier
+	 * and the one in srcu_readers_active_idx_check() provide the
+	 * guarantee for __srcu_read_lock().
+	 */
+	smp_mb(); /* D */  /* Pairs with C. */
+}
+
+/*
+ * End an SRCU grace period.
+ */
+static void srcu_gp_end(struct srcu_struct *sp)
+{
+	rcu_seq_end(&sp->srcu_gp_seq);
+
+	spin_lock_irq(&sp->queue_lock);
+	rcu_segcblist_advance(&sp->srcu_cblist,
+			      rcu_seq_current(&sp->srcu_gp_seq));
+	spin_unlock_irq(&sp->queue_lock);
+}
+
+/*
+ * Enqueue an SRCU callback on the specified srcu_struct structure,
+ * initiating grace-period processing if it is not already running.
+ *
+ * Note that all CPUs must agree that the grace period extended beyond
+ * all pre-existing SRCU read-side critical section.  On systems with
+ * more than one CPU, this means that when "func()" is invoked, each CPU
+ * is guaranteed to have executed a full memory barrier since the end of
+ * its last corresponding SRCU read-side critical section whose beginning
+ * preceded the call to call_rcu().  It also means that each CPU executing
+ * an SRCU read-side critical section that continues beyond the start of
+ * "func()" must have executed a memory barrier after the call_rcu()
+ * but before the beginning of that SRCU read-side critical section.
+ * Note that these guarantees include CPUs that are offline, idle, or
+ * executing in user mode, as well as CPUs that are executing in the kernel.
+ *
+ * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
+ * resulting SRCU callback function "func()", then both CPU A and CPU
+ * B are guaranteed to execute a full memory barrier during the time
+ * interval between the call to call_rcu() and the invocation of "func()".
+ * This guarantee applies even if CPU A and CPU B are the same CPU (but
+ * again only if the system has more than one CPU).
+ *
+ * Of course, these guarantees apply only for invocations of call_srcu(),
+ * srcu_read_lock(), and srcu_read_unlock() that are all passed the same
+ * srcu_struct structure.
+ */
+void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
+	       rcu_callback_t func)
+{
+	unsigned long flags;
+
+	head->next = NULL;
+	head->func = func;
+	spin_lock_irqsave(&sp->queue_lock, flags);
+	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
+	rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
+	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
+		srcu_gp_start(sp);
+		queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
+	}
+	spin_unlock_irqrestore(&sp->queue_lock, flags);
+}
+EXPORT_SYMBOL_GPL(call_srcu);
+
+static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay);
+
+/*
+ * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
+ */
+static void __synchronize_srcu(struct srcu_struct *sp)
+{
+	struct rcu_synchronize rcu;
+	struct rcu_head *head = &rcu.head;
+
+	RCU_LOCKDEP_WARN(lock_is_held(&sp->dep_map) ||
+			 lock_is_held(&rcu_bh_lock_map) ||
+			 lock_is_held(&rcu_lock_map) ||
+			 lock_is_held(&rcu_sched_lock_map),
+			 "Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");
+
+	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
+		return;
+	might_sleep();
+	init_completion(&rcu.completion);
+
+	head->next = NULL;
+	head->func = wakeme_after_rcu;
+	spin_lock_irq(&sp->queue_lock);
+	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
+	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
+		/* steal the processing owner */
+		rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
+		srcu_gp_start(sp);
+		spin_unlock_irq(&sp->queue_lock);
+		/* give the processing owner to work_struct */
+		srcu_reschedule(sp, 0);
+	} else {
+		rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
+		spin_unlock_irq(&sp->queue_lock);
+	}
+
+	wait_for_completion(&rcu.completion);
+	smp_mb(); /* Caller's later accesses after GP. */
+}
+
+/**
+ * synchronize_srcu_expedited - Brute-force SRCU grace period
+ * @sp: srcu_struct with which to synchronize.
+ *
+ * Wait for an SRCU grace period to elapse, but be more aggressive about
+ * spinning rather than blocking when waiting.
+ *
+ * Note that synchronize_srcu_expedited() has the same deadlock and
+ * memory-ordering properties as does synchronize_srcu().
+ */
+void synchronize_srcu_expedited(struct srcu_struct *sp)
+{
+	bool do_norm = rcu_gp_is_normal();
+
+	if (!do_norm) {
+		atomic_inc(&sp->srcu_exp_cnt);
+		smp_mb__after_atomic(); /* increment before GP. */
+	}
+	__synchronize_srcu(sp);
+	if (!do_norm) {
+		smp_mb__before_atomic(); /* GP before decrement. */
+		atomic_dec(&sp->srcu_exp_cnt);
+	}
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
+
+/**
+ * synchronize_srcu - wait for prior SRCU read-side critical-section completion
+ * @sp: srcu_struct with which to synchronize.
+ *
+ * Wait for the count to drain to zero of both indexes. To avoid the
+ * possible starvation of synchronize_srcu(), it waits for the count of
+ * the index=((->completed & 1) ^ 1) to drain to zero at first,
+ * and then flip the completed and wait for the count of the other index.
+ *
+ * Can block; must be called from process context.
+ *
+ * Note that it is illegal to call synchronize_srcu() from the corresponding
+ * SRCU read-side critical section; doing so will result in deadlock.
+ * However, it is perfectly legal to call synchronize_srcu() on one
+ * srcu_struct from some other srcu_struct's read-side critical section,
+ * as long as the resulting graph of srcu_structs is acyclic.
+ *
+ * There are memory-ordering constraints implied by synchronize_srcu().
+ * On systems with more than one CPU, when synchronize_srcu() returns,
+ * each CPU is guaranteed to have executed a full memory barrier since
+ * the end of its last corresponding SRCU-sched read-side critical section
+ * whose beginning preceded the call to synchronize_srcu().  In addition,
+ * each CPU having an SRCU read-side critical section that extends beyond
+ * the return from synchronize_srcu() is guaranteed to have executed a
+ * full memory barrier after the beginning of synchronize_srcu() and before
+ * the beginning of that SRCU read-side critical section.  Note that these
+ * guarantees include CPUs that are offline, idle, or executing in user mode,
+ * as well as CPUs that are executing in the kernel.
+ *
+ * Furthermore, if CPU A invoked synchronize_srcu(), which returned
+ * to its caller on CPU B, then both CPU A and CPU B are guaranteed
+ * to have executed a full memory barrier during the execution of
+ * synchronize_srcu().  This guarantee applies even if CPU A and CPU B
+ * are the same CPU, but again only if the system has more than one CPU.
+ *
+ * Of course, these memory-ordering guarantees apply only when
+ * synchronize_srcu(), srcu_read_lock(), and srcu_read_unlock() are
+ * passed the same srcu_struct structure.
+ */
+void synchronize_srcu(struct srcu_struct *sp)
+{
+	if (rcu_gp_is_expedited())
+		synchronize_srcu_expedited(sp);
+	else
+		__synchronize_srcu(sp);
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu);
+
+/**
+ * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
+ * @sp: srcu_struct on which to wait for in-flight callbacks.
+ */
+void srcu_barrier(struct srcu_struct *sp)
+{
+	synchronize_srcu(sp);
+}
+EXPORT_SYMBOL_GPL(srcu_barrier);
+
+/**
+ * srcu_batches_completed - return batches completed.
+ * @sp: srcu_struct on which to report batch completion.
+ *
+ * Report the number of batches, correlated with, but not necessarily
+ * precisely the same as, the number of grace periods that have elapsed.
+ */
+unsigned long srcu_batches_completed(struct srcu_struct *sp)
+{
+	return sp->completed;
+}
+EXPORT_SYMBOL_GPL(srcu_batches_completed);
+
+/*
+ * Core SRCU state machine.  Advance callbacks from ->batch_check0 to
+ * ->batch_check1 and then to ->batch_done as readers drain.
+ */
+static void srcu_advance_batches(struct srcu_struct *sp)
+{
+	int idx;
+
+	/*
+	 * Because readers might be delayed for an extended period after
+	 * fetching ->completed for their index, at any point in time there
+	 * might well be readers using both idx=0 and idx=1.  We therefore
+	 * need to wait for readers to clear from both index values before
+	 * invoking a callback.
+	 *
+	 * The load-acquire ensures that we see the accesses performed
+	 * by the prior grace period.
+	 */
+	idx = rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq)); /* ^^^ */
+	if (idx == SRCU_STATE_IDLE) {
+		spin_lock_irq(&sp->queue_lock);
+		if (rcu_segcblist_empty(&sp->srcu_cblist)) {
+			spin_unlock_irq(&sp->queue_lock);
+			return;
+		}
+		idx = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
+		if (idx == SRCU_STATE_IDLE)
+			srcu_gp_start(sp);
+		spin_unlock_irq(&sp->queue_lock);
+		if (idx != SRCU_STATE_IDLE)
+			return; /* Someone else started the grace period. */
+	}
+
+	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
+		idx = 1 ^ (sp->completed & 1);
+		if (!try_check_zero(sp, idx, 1))
+			return; /* readers present, retry later. */
+		srcu_flip(sp);
+		rcu_seq_set_state(&sp->srcu_gp_seq, SRCU_STATE_SCAN2);
+	}
+
+	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN2) {
+
+		/*
+		 * SRCU read-side critical sections are normally short,
+		 * so check at least twice in quick succession after a flip.
+		 */
+		idx = 1 ^ (sp->completed & 1);
+		if (!try_check_zero(sp, idx, 2))
+			return; /* readers present, retry after later. */
+		srcu_gp_end(sp);
+	}
+}
+
+/*
+ * Invoke a limited number of SRCU callbacks that have passed through
+ * their grace period.  If there are more to do, SRCU will reschedule
+ * the workqueue.  Note that needed memory barriers have been executed
+ * in this task's context by srcu_readers_active_idx_check().
+ */
+static void srcu_invoke_callbacks(struct srcu_struct *sp)
+{
+	struct rcu_cblist ready_cbs;
+	struct rcu_head *rhp;
+
+	spin_lock_irq(&sp->queue_lock);
+	if (!rcu_segcblist_ready_cbs(&sp->srcu_cblist)) {
+		spin_unlock_irq(&sp->queue_lock);
+		return;
+	}
+	rcu_cblist_init(&ready_cbs);
+	rcu_segcblist_extract_done_cbs(&sp->srcu_cblist, &ready_cbs);
+	spin_unlock_irq(&sp->queue_lock);
+	rhp = rcu_cblist_dequeue(&ready_cbs);
+	for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
+		local_bh_disable();
+		rhp->func(rhp);
+		local_bh_enable();
+	}
+	spin_lock_irq(&sp->queue_lock);
+	rcu_segcblist_insert_count(&sp->srcu_cblist, &ready_cbs);
+	spin_unlock_irq(&sp->queue_lock);
+}
+
+/*
+ * Finished one round of SRCU grace period.  Start another if there are
+ * more SRCU callbacks queued, otherwise put SRCU into not-running state.
+ */
+static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
+{
+	bool pending = true;
+	int state;
+
+	if (rcu_segcblist_empty(&sp->srcu_cblist)) {
+		spin_lock_irq(&sp->queue_lock);
+		state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
+		if (rcu_segcblist_empty(&sp->srcu_cblist) &&
+		    state == SRCU_STATE_IDLE)
+			pending = false;
+		spin_unlock_irq(&sp->queue_lock);
+	}
+
+	if (pending)
+		queue_delayed_work(system_power_efficient_wq, &sp->work, delay);
+}
+
+/*
+ * This is the work-queue function that handles SRCU grace periods.
+ */
+void process_srcu(struct work_struct *work)
+{
+	struct srcu_struct *sp;
+
+	sp = container_of(work, struct srcu_struct, work.work);
+
+	srcu_advance_batches(sp);
+	srcu_invoke_callbacks(sp);
+	srcu_reschedule(sp, atomic_read(&sp->srcu_exp_cnt) ? 0 : SRCU_INTERVAL);
+}
+EXPORT_SYMBOL_GPL(process_srcu);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH tip/core/rcu 40/40] srcu: Parallelize callback handling
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (38 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 39/40] srcu: Introduce CLASSIC_SRCU Kconfig option Paul E. McKenney
@ 2017-04-12 17:40 ` Paul E. McKenney
  2017-04-13  9:50   ` Peter Zijlstra
                     ` (2 more replies)
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
  40 siblings, 3 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-12 17:40 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

Peter Zijlstra proposed using SRCU to reduce mmap_sem contention [1],
however, there are workloads that could result in a high volume of
concurrent invocations of call_srcu(), which with current SRCU would
result in excessive lock contention on the srcu_struct structure's
->queue_lock, which protects SRCU's callback lists.  This commit therefore
moves SRCU to per-CPU callback lists, thus greatly reducing contention.

Because a given SRCU instance no longer has a single centralized callback
list, starting grace periods and invoking callbacks each require a bit
more work.  These are handled using an srcu_node tree that is in some ways
similar to the rcu_node trees used by RCU-bh, RCU-preempt, and RCU-sched
(for example, the srcu_node tree shape is controlled by exactly the
same Kconfig options and boot parameters that control the shape of the
rcu_node tree).

In addition, the old per-CPU srcu_array structure is now named srcu_data
and contains an rcu_segcblist structure named ->srcu_cblist for its
callbacks (and a spinlock to protect this).  The srcu_struct gets
an srcu_gp_seq that is used to associate callback segments with the
corresponding completion-time grace-period number.  These completion-time
grace-period numbers are propagated up the srcu_node tree so that the
grace-period workqueue handler can determine whether additional grace
periods are needed on the one hand and where to look for callbacks that
are ready to be invoked.

The srcu_barrier() function must now wait on all instances of the
per-CPU ->srcu_cblist.  Because each ->srcu_cblist is protected
by ->lock, srcu_barrier() can remotely add the needed callbacks.
In theory, it could also remotely start grace periods, but this gets
complex and racy.  And interestingly enough, it is never necessary to
start a grace period in this case because srcu_barrier() only enqueues
a callback when a callback is already present.  And a grace period has
to have already been started for this pre-existing callback.  And it is
only the callback that srcu_barrier() needs to wait on, not any particular
grace period.  Therefore, a new rcu_segcblist_entrain() function enqueues
the srcu_barrier() function's callback into the same segment occupied by
the pre-existing callback.  The special case where all the pre-existing
callbacks are on a different list being invoked is handled by enqueuing
srcu_barrier()'s callback into the RCU_DONE_TAIL segment, relying on
the done-callbacks check that takes place after all callbacks are inovked.

Note that the readers use the same algorithm as before.  Note that there
is a separate srcu_idx that tells the readers what counter to increment.
This unfortunately cannot be combined with srcu_gp_seq because they
need to be incremented at different times.

This commit introduces some ugly #ifdefs in rcutorture.  These will go
away when I feel good enough about Tree SRCU to ditch Classic SRCU.

[1] https://lwn.net/Articles/309030/

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcu_segcblist.h |  42 ++-
 include/linux/srcutree.h      |  80 ++++--
 kernel/rcu/rcutorture.c       |  20 +-
 kernel/rcu/srcutree.c         | 639 +++++++++++++++++++++++++++++++++---------
 kernel/rcu/tree.c             |   6 +
 kernel/rcu/tree.h             |   8 +
 6 files changed, 645 insertions(+), 150 deletions(-)

diff --git a/include/linux/rcu_segcblist.h b/include/linux/rcu_segcblist.h
index 74b1e7243955..ced8f313fd05 100644
--- a/include/linux/rcu_segcblist.h
+++ b/include/linux/rcu_segcblist.h
@@ -402,6 +402,37 @@ static inline void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
 }
 
 /*
+ * Entrain the specified callback onto the specified rcu_segcblist at
+ * the end of the last non-empty segment.  If the entire rcu_segcblist
+ * is empty, make no change, but return false.
+ *
+ * This is intended for use by rcu_barrier()-like primitives, -not-
+ * for normal grace-period use.  IMPORTANT:  The callback you enqueue
+ * will wait for all prior callbacks, NOT necessarily for a grace
+ * period.  You have been warned.
+ */
+static inline bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp,
+					 struct rcu_head *rhp, bool lazy)
+{
+	int i;
+
+	if (rcu_segcblist_n_cbs(rsclp) == 0)
+		return false;
+	WRITE_ONCE(rsclp->len, rsclp->len + 1);
+	if (lazy)
+		rsclp->len_lazy++;
+	smp_mb(); /* Ensure counts are updated before callback is entrained. */
+	rhp->next = NULL;
+	for (i = RCU_NEXT_TAIL; i > RCU_DONE_TAIL; i--)
+		if (rsclp->tails[i] != rsclp->tails[i - 1])
+			break;
+	*rsclp->tails[i] = rhp;
+	for (; i <= RCU_NEXT_TAIL; i++)
+		rsclp->tails[i] = &rhp->next;
+	return true;
+}
+
+/*
  * Extract only the counts from the specified rcu_segcblist structure,
  * and place them in the specified rcu_cblist structure.  This function
  * supports both callback orphaning and invocation, hence the separation
@@ -537,7 +568,8 @@ static inline void rcu_segcblist_advance(struct rcu_segcblist *rsclp,
 	int i, j;
 
 	WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
-	WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL));
+	if (rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL))
+		return;
 
 	/*
 	 * Find all callbacks whose ->gp_seq numbers indicate that they
@@ -582,8 +614,9 @@ static inline void rcu_segcblist_advance(struct rcu_segcblist *rsclp,
  * them to complete at the end of the earlier grace period.
  *
  * This function operates on an rcu_segcblist structure, and also the
- * grace-period sequence number at which new callbacks would become
- * ready to invoke.
+ * grace-period sequence number seq at which new callbacks would become
+ * ready to invoke.  Returns true if there are callbacks that won't be
+ * ready to invoke until seq, false otherwise.
  */
 static inline bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp,
 					    unsigned long seq)
@@ -591,7 +624,8 @@ static inline bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp,
 	int i;
 
 	WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
-	WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL));
+	if (rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL))
+		return false;
 
 	/*
 	 * Find the segment preceding the oldest segment of callbacks
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index f2b3bd6c6bc2..0400e211aa44 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -24,25 +24,75 @@
 #ifndef _LINUX_SRCU_TREE_H
 #define _LINUX_SRCU_TREE_H
 
-struct srcu_array {
-	unsigned long lock_count[2];
-	unsigned long unlock_count[2];
+#include <linux/rcu_node_tree.h>
+#include <linux/completion.h>
+
+struct srcu_node;
+struct srcu_struct;
+
+/*
+ * Per-CPU structure feeding into leaf srcu_node, similar in function
+ * to rcu_node.
+ */
+struct srcu_data {
+	/* Read-side state. */
+	unsigned long srcu_lock_count[2];	/* Locks per CPU. */
+	unsigned long srcu_unlock_count[2];	/* Unlocks per CPU. */
+
+	/* Update-side state. */
+	spinlock_t lock ____cacheline_internodealigned_in_smp;
+	struct rcu_segcblist srcu_cblist;	/* List of callbacks.*/
+	unsigned long srcu_gp_seq_needed;	/* Furthest future GP needed. */
+	bool srcu_cblist_invoking;		/* Invoking these CBs? */
+	struct delayed_work work;		/* Context for CB invoking. */
+	struct rcu_head srcu_barrier_head;	/* For srcu_barrier() use. */
+	struct srcu_node *mynode;		/* Leaf srcu_node. */
+	int cpu;
+	struct srcu_struct *sp;
 };
 
+/*
+ * Node in SRCU combining tree, similar in function to rcu_data.
+ */
+struct srcu_node {
+	spinlock_t lock;
+	unsigned long srcu_have_cbs[4];		/* GP seq for children */
+						/*  having CBs, but only */
+						/*  is > ->srcu_gq_seq. */
+	struct srcu_node *srcu_parent;		/* Next up in tree. */
+	int grplo;				/* Least CPU for node. */
+	int grphi;				/* Biggest CPU for node. */
+};
+
+/*
+ * Per-SRCU-domain structure, similar in function to rcu_state.
+ */
 struct srcu_struct {
-	unsigned long completed;
-	unsigned long srcu_gp_seq;
-	atomic_t srcu_exp_cnt;
-	struct srcu_array __percpu *per_cpu_ref;
-	spinlock_t queue_lock; /* protect ->srcu_cblist */
-	struct rcu_segcblist srcu_cblist;
+	struct srcu_node node[NUM_RCU_NODES];	/* Combining tree. */
+	struct srcu_node *level[RCU_NUM_LVLS + 1];
+						/* First node at each level. */
+	struct mutex srcu_cb_mutex;		/* Serialize CB preparation. */
+	spinlock_t gp_lock;			/* protect ->srcu_cblist */
+	struct mutex srcu_gp_mutex;		/* Serialize GP work. */
+	unsigned int srcu_idx;			/* Current rdr array element. */
+	unsigned long srcu_gp_seq;		/* Grace-period seq #. */
+	unsigned long srcu_gp_seq_needed;	/* Latest gp_seq needed. */
+	atomic_t srcu_exp_cnt;			/* # ongoing expedited GPs. */
+	struct srcu_data __percpu *sda;		/* Per-CPU srcu_data array. */
+	unsigned long srcu_barrier_seq;		/* srcu_barrier seq #. */
+	struct mutex srcu_barrier_mutex;	/* Serialize barrier ops. */
+	struct completion srcu_barrier_completion;
+						/* Awaken barrier rq at end. */
+	atomic_t srcu_barrier_cpu_cnt;		/* # CPUs not yet posting a */
+						/*  callback for the barrier */
+						/*  operation. */
 	struct delayed_work work;
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map dep_map;
 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 };
 
-/* Values for -> state variable. */
+/* Values for state variable (bottom bits of ->srcu_gp_seq). */
 #define SRCU_STATE_IDLE		0
 #define SRCU_STATE_SCAN1	1
 #define SRCU_STATE_SCAN2	2
@@ -51,11 +101,9 @@ void process_srcu(struct work_struct *work);
 
 #define __SRCU_STRUCT_INIT(name)					\
 	{								\
-		.completed = -300,					\
-		.per_cpu_ref = &name##_srcu_array,			\
-		.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock),	\
-		.srcu_cblist = RCU_SEGCBLIST_INITIALIZER(name.srcu_cblist),\
-		.work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
+		.sda = &name##_srcu_data,				\
+		.gp_lock = __SPIN_LOCK_UNLOCKED(name.gp_lock),		\
+		.srcu_gp_seq_needed = 0 - 1,				\
 		__SRCU_DEP_MAP_INIT(name)				\
 	}
 
@@ -79,7 +127,7 @@ void process_srcu(struct work_struct *work);
  * See include/linux/percpu-defs.h for the rules on per-CPU variables.
  */
 #define __DEFINE_SRCU(name, is_static)					\
-	static DEFINE_PER_CPU(struct srcu_array, name##_srcu_array);\
+	static DEFINE_PER_CPU(struct srcu_data, name##_srcu_data);\
 	is_static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
 #define DEFINE_SRCU(name)		__DEFINE_SRCU(name, /* not static */)
 #define DEFINE_STATIC_SRCU(name)	__DEFINE_SRCU(name, static)
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 6f344b6748a8..e9d4527cdd43 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -563,17 +563,30 @@ static void srcu_torture_stats(void)
 	int idx;
 
 #if defined(CONFIG_TREE_SRCU) || defined(CONFIG_CLASSIC_SRCU)
+#ifdef CONFIG_TREE_SRCU
+	idx = srcu_ctlp->srcu_idx & 0x1;
+#else /* #ifdef CONFIG_TREE_SRCU */
 	idx = srcu_ctlp->completed & 0x1;
+#endif /* #else #ifdef CONFIG_TREE_SRCU */
 	pr_alert("%s%s Tree SRCU per-CPU(idx=%d):",
 		 torture_type, TORTURE_FLAG, idx);
 	for_each_possible_cpu(cpu) {
 		unsigned long l0, l1;
 		unsigned long u0, u1;
 		long c0, c1;
-		struct srcu_array *counts = per_cpu_ptr(srcu_ctlp->per_cpu_ref, cpu);
+#ifdef CONFIG_TREE_SRCU
+		struct srcu_data *counts;
 
+		counts = per_cpu_ptr(srcu_ctlp->sda, cpu);
+		u0 = counts->srcu_unlock_count[!idx];
+		u1 = counts->srcu_unlock_count[idx];
+#else /* #ifdef CONFIG_TREE_SRCU */
+		struct srcu_array *counts;
+
+		counts = per_cpu_ptr(srcu_ctlp->per_cpu_ref, cpu);
 		u0 = counts->unlock_count[!idx];
 		u1 = counts->unlock_count[idx];
+#endif /* #else #ifdef CONFIG_TREE_SRCU */
 
 		/*
 		 * Make sure that a lock is always counted if the corresponding
@@ -581,8 +594,13 @@ static void srcu_torture_stats(void)
 		 */
 		smp_rmb();
 
+#ifdef CONFIG_TREE_SRCU
+		l0 = counts->srcu_lock_count[!idx];
+		l1 = counts->srcu_lock_count[idx];
+#else /* #ifdef CONFIG_TREE_SRCU */
 		l0 = counts->lock_count[!idx];
 		l1 = counts->lock_count[idx];
+#endif /* #else #ifdef CONFIG_TREE_SRCU */
 
 		c0 = l0 - u0;
 		c1 = l1 - u1;
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index da676b0d016b..f9c684d79faa 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -36,19 +36,110 @@
 #include <linux/delay.h>
 #include <linux/srcu.h>
 
-#include <linux/rcu_node_tree.h>
 #include "rcu.h"
 
-static int init_srcu_struct_fields(struct srcu_struct *sp)
+static void srcu_invoke_callbacks(struct work_struct *work);
+static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay);
+
+/*
+ * Initialize SRCU combining tree.  Note that statically allocated
+ * srcu_struct structures might already have srcu_read_lock() and
+ * srcu_read_unlock() running against them.  So if the is_static parameter
+ * is set, don't initialize ->srcu_lock_count[] and ->srcu_unlock_count[].
+ */
+static void init_srcu_struct_nodes(struct srcu_struct *sp, bool is_static)
 {
-	sp->completed = 0;
+	int cpu;
+	int i;
+	int level = 0;
+	int levelspread[RCU_NUM_LVLS];
+	struct srcu_data *sdp;
+	struct srcu_node *snp;
+	struct srcu_node *snp_first;
+
+	/* Work out the overall tree geometry. */
+	sp->level[0] = &sp->node[0];
+	for (i = 1; i < rcu_num_lvls; i++)
+		sp->level[i] = sp->level[i - 1] + num_rcu_lvl[i - 1];
+	rcu_init_levelspread(levelspread, num_rcu_lvl);
+
+	/* Each pass through this loop initializes one srcu_node structure. */
+	rcu_for_each_node_breadth_first(sp, snp) {
+		spin_lock_init(&snp->lock);
+		for (i = 0; i < ARRAY_SIZE(snp->srcu_have_cbs); i++)
+			snp->srcu_have_cbs[i] = 0;
+		snp->grplo = -1;
+		snp->grphi = -1;
+		if (snp == &sp->node[0]) {
+			/* Root node, special case. */
+			snp->srcu_parent = NULL;
+			continue;
+		}
+
+		/* Non-root node. */
+		if (snp == sp->level[level + 1])
+			level++;
+		snp->srcu_parent = sp->level[level - 1] +
+				   (snp - sp->level[level]) /
+				   levelspread[level - 1];
+	}
+
+	/*
+	 * Initialize the per-CPU srcu_data array, which feeds into the
+	 * leaves of the srcu_node tree.
+	 */
+	WARN_ON_ONCE(ARRAY_SIZE(sdp->srcu_lock_count) !=
+		     ARRAY_SIZE(sdp->srcu_unlock_count));
+	level = rcu_num_lvls - 1;
+	snp_first = sp->level[level];
+	for_each_possible_cpu(cpu) {
+		sdp = per_cpu_ptr(sp->sda, cpu);
+		spin_lock_init(&sdp->lock);
+		rcu_segcblist_init(&sdp->srcu_cblist);
+		sdp->srcu_cblist_invoking = false;
+		sdp->srcu_gp_seq_needed = sp->srcu_gp_seq;
+		sdp->mynode = &snp_first[cpu / levelspread[level]];
+		for (snp = sdp->mynode; snp != NULL; snp = snp->srcu_parent) {
+			if (snp->grplo < 0)
+				snp->grplo = cpu;
+			snp->grphi = cpu;
+		}
+		sdp->cpu = cpu;
+		INIT_DELAYED_WORK(&sdp->work, srcu_invoke_callbacks);
+		sdp->sp = sp;
+		if (is_static)
+			continue;
+
+		/* Dynamically allocated, better be no srcu_read_locks()! */
+		for (i = 0; i < ARRAY_SIZE(sdp->srcu_lock_count); i++) {
+			sdp->srcu_lock_count[i] = 0;
+			sdp->srcu_unlock_count[i] = 0;
+		}
+	}
+}
+
+/*
+ * Initialize non-compile-time initialized fields, including the
+ * associated srcu_node and srcu_data structures.  The is_static
+ * parameter is passed through to init_srcu_struct_nodes(), and
+ * also tells us that ->sda has already been wired up to srcu_data.
+ */
+static int init_srcu_struct_fields(struct srcu_struct *sp, bool is_static)
+{
+	mutex_init(&sp->srcu_cb_mutex);
+	mutex_init(&sp->srcu_gp_mutex);
+	sp->srcu_idx = 0;
 	sp->srcu_gp_seq = 0;
 	atomic_set(&sp->srcu_exp_cnt, 0);
-	spin_lock_init(&sp->queue_lock);
-	rcu_segcblist_init(&sp->srcu_cblist);
+	sp->srcu_barrier_seq = 0;
+	mutex_init(&sp->srcu_barrier_mutex);
+	atomic_set(&sp->srcu_barrier_cpu_cnt, 0);
 	INIT_DELAYED_WORK(&sp->work, process_srcu);
-	sp->per_cpu_ref = alloc_percpu(struct srcu_array);
-	return sp->per_cpu_ref ? 0 : -ENOMEM;
+	if (!is_static)
+		sp->sda = alloc_percpu(struct srcu_data);
+	init_srcu_struct_nodes(sp, is_static);
+	smp_store_release(&sp->srcu_gp_seq_needed, 0); /* Init done. */
+	return sp->sda ? 0 : -ENOMEM;
 }
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
@@ -59,7 +150,8 @@ int __init_srcu_struct(struct srcu_struct *sp, const char *name,
 	/* Don't re-initialize a lock while it is held. */
 	debug_check_no_locks_freed((void *)sp, sizeof(*sp));
 	lockdep_init_map(&sp->dep_map, name, key, 0);
-	return init_srcu_struct_fields(sp);
+	spin_lock_init(&sp->gp_lock);
+	return init_srcu_struct_fields(sp, false);
 }
 EXPORT_SYMBOL_GPL(__init_srcu_struct);
 
@@ -75,15 +167,41 @@ EXPORT_SYMBOL_GPL(__init_srcu_struct);
  */
 int init_srcu_struct(struct srcu_struct *sp)
 {
-	return init_srcu_struct_fields(sp);
+	spin_lock_init(&sp->gp_lock);
+	return init_srcu_struct_fields(sp, false);
 }
 EXPORT_SYMBOL_GPL(init_srcu_struct);
 
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
 /*
- * Returns approximate total of the readers' ->lock_count[] values for the
- * rank of per-CPU counters specified by idx.
+ * First-use initialization of statically allocated srcu_struct
+ * structure.  Wiring up the combining tree is more than can be
+ * done with compile-time initialization, so this check is added
+ * to each update-side SRCU primitive.  Use ->gp_lock, which -is-
+ * compile-time initialized, to resolve races involving multiple
+ * CPUs trying to garner first-use privileges.
+ */
+static void check_init_srcu_struct(struct srcu_struct *sp)
+{
+	unsigned long flags;
+
+	WARN_ON_ONCE(rcu_scheduler_active == RCU_SCHEDULER_INIT);
+	/* The smp_load_acquire() pairs with the smp_store_release(). */
+	if (!rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq_needed))) /*^^^*/
+		return; /* Already initialized. */
+	spin_lock_irqsave(&sp->gp_lock, flags);
+	if (!rcu_seq_state(sp->srcu_gp_seq_needed)) {
+		spin_unlock_irqrestore(&sp->gp_lock, flags);
+		return;
+	}
+	init_srcu_struct_fields(sp, true);
+	spin_unlock_irqrestore(&sp->gp_lock, flags);
+}
+
+/*
+ * Returns approximate total of the readers' ->srcu_lock_count[] values
+ * for the rank of per-CPU counters specified by idx.
  */
 static unsigned long srcu_readers_lock_idx(struct srcu_struct *sp, int idx)
 {
@@ -91,16 +209,16 @@ static unsigned long srcu_readers_lock_idx(struct srcu_struct *sp, int idx)
 	unsigned long sum = 0;
 
 	for_each_possible_cpu(cpu) {
-		struct srcu_array *cpuc = per_cpu_ptr(sp->per_cpu_ref, cpu);
+		struct srcu_data *cpuc = per_cpu_ptr(sp->sda, cpu);
 
-		sum += READ_ONCE(cpuc->lock_count[idx]);
+		sum += READ_ONCE(cpuc->srcu_lock_count[idx]);
 	}
 	return sum;
 }
 
 /*
- * Returns approximate total of the readers' ->unlock_count[] values for the
- * rank of per-CPU counters specified by idx.
+ * Returns approximate total of the readers' ->srcu_unlock_count[] values
+ * for the rank of per-CPU counters specified by idx.
  */
 static unsigned long srcu_readers_unlock_idx(struct srcu_struct *sp, int idx)
 {
@@ -108,9 +226,9 @@ static unsigned long srcu_readers_unlock_idx(struct srcu_struct *sp, int idx)
 	unsigned long sum = 0;
 
 	for_each_possible_cpu(cpu) {
-		struct srcu_array *cpuc = per_cpu_ptr(sp->per_cpu_ref, cpu);
+		struct srcu_data *cpuc = per_cpu_ptr(sp->sda, cpu);
 
-		sum += READ_ONCE(cpuc->unlock_count[idx]);
+		sum += READ_ONCE(cpuc->srcu_unlock_count[idx]);
 	}
 	return sum;
 }
@@ -145,14 +263,14 @@ static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx)
 	 * the current index but not have incremented the lock counter yet.
 	 *
 	 * Possible bug: There is no guarantee that there haven't been
-	 * ULONG_MAX increments of ->lock_count[] since the unlocks were
+	 * ULONG_MAX increments of ->srcu_lock_count[] since the unlocks were
 	 * counted, meaning that this could return true even if there are
 	 * still active readers.  Since there are no memory barriers around
-	 * srcu_flip(), the CPU is not required to increment ->completed
+	 * srcu_flip(), the CPU is not required to increment ->srcu_idx
 	 * before running srcu_readers_unlock_idx(), which means that there
 	 * could be an arbitrarily large number of critical sections that
 	 * execute after srcu_readers_unlock_idx() but use the old value
-	 * of ->completed.
+	 * of ->srcu_idx.
 	 */
 	return srcu_readers_lock_idx(sp, idx) == unlocks;
 }
@@ -172,12 +290,12 @@ static bool srcu_readers_active(struct srcu_struct *sp)
 	unsigned long sum = 0;
 
 	for_each_possible_cpu(cpu) {
-		struct srcu_array *cpuc = per_cpu_ptr(sp->per_cpu_ref, cpu);
+		struct srcu_data *cpuc = per_cpu_ptr(sp->sda, cpu);
 
-		sum += READ_ONCE(cpuc->lock_count[0]);
-		sum += READ_ONCE(cpuc->lock_count[1]);
-		sum -= READ_ONCE(cpuc->unlock_count[0]);
-		sum -= READ_ONCE(cpuc->unlock_count[1]);
+		sum += READ_ONCE(cpuc->srcu_lock_count[0]);
+		sum += READ_ONCE(cpuc->srcu_lock_count[1]);
+		sum -= READ_ONCE(cpuc->srcu_unlock_count[0]);
+		sum -= READ_ONCE(cpuc->srcu_unlock_count[1]);
 	}
 	return sum;
 }
@@ -193,18 +311,21 @@ static bool srcu_readers_active(struct srcu_struct *sp)
  */
 void cleanup_srcu_struct(struct srcu_struct *sp)
 {
+	int cpu;
+
 	WARN_ON_ONCE(atomic_read(&sp->srcu_exp_cnt));
 	if (WARN_ON(srcu_readers_active(sp)))
 		return; /* Leakage unless caller handles error. */
-	if (WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist)))
-		return; /* Leakage unless caller handles error. */
 	flush_delayed_work(&sp->work);
-	if (WARN_ON(rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) != SRCU_STATE_IDLE)) {
-		pr_info("cleanup_srcu_struct: Active srcu_struct %lu CBs %c state: %d\n", rcu_segcblist_n_cbs(&sp->srcu_cblist), ".E"[rcu_segcblist_empty(&sp->srcu_cblist)], rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)));
+	for_each_possible_cpu(cpu)
+		flush_delayed_work(&per_cpu_ptr(sp->sda, cpu)->work);
+	if (WARN_ON(rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) != SRCU_STATE_IDLE) ||
+	    WARN_ON(srcu_readers_active(sp))) {
+		pr_info("cleanup_srcu_struct: Active srcu_struct %p state: %d\n", sp, rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)));
 		return; /* Caller forgot to stop doing call_srcu()? */
 	}
-	free_percpu(sp->per_cpu_ref);
-	sp->per_cpu_ref = NULL;
+	free_percpu(sp->sda);
+	sp->sda = NULL;
 }
 EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
 
@@ -217,8 +338,8 @@ int __srcu_read_lock(struct srcu_struct *sp)
 {
 	int idx;
 
-	idx = READ_ONCE(sp->completed) & 0x1;
-	__this_cpu_inc(sp->per_cpu_ref->lock_count[idx]);
+	idx = READ_ONCE(sp->srcu_idx) & 0x1;
+	__this_cpu_inc(sp->sda->srcu_lock_count[idx]);
 	smp_mb(); /* B */  /* Avoid leaking the critical section. */
 	return idx;
 }
@@ -233,7 +354,7 @@ EXPORT_SYMBOL_GPL(__srcu_read_lock);
 void __srcu_read_unlock(struct srcu_struct *sp, int idx)
 {
 	smp_mb(); /* C */  /* Avoid leaking the critical section. */
-	this_cpu_inc(sp->per_cpu_ref->unlock_count[idx]);
+	this_cpu_inc(sp->sda->srcu_unlock_count[idx]);
 }
 EXPORT_SYMBOL_GPL(__srcu_read_unlock);
 
@@ -251,19 +372,207 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
  */
 static void srcu_gp_start(struct srcu_struct *sp)
 {
+	struct srcu_data *sdp = this_cpu_ptr(sp->sda);
 	int state;
 
-	rcu_segcblist_accelerate(&sp->srcu_cblist,
-				 rcu_seq_snap(&sp->srcu_gp_seq));
+	RCU_LOCKDEP_WARN(!lockdep_is_held(&sp->gp_lock),
+			 "Invoked srcu_gp_start() without ->gp_lock!");
+	WARN_ON_ONCE(ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed));
+	rcu_segcblist_advance(&sdp->srcu_cblist,
+			      rcu_seq_current(&sp->srcu_gp_seq));
+	(void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
+				       rcu_seq_snap(&sp->srcu_gp_seq));
 	rcu_seq_start(&sp->srcu_gp_seq);
 	state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
 	WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
 }
 
 /*
+ * Track online CPUs to guide callback workqueue placement.
+ */
+DEFINE_PER_CPU(bool, srcu_online);
+
+void srcu_online_cpu(unsigned int cpu)
+{
+	WRITE_ONCE(per_cpu(srcu_online, cpu), true);
+}
+
+void srcu_offline_cpu(unsigned int cpu)
+{
+	WRITE_ONCE(per_cpu(srcu_online, cpu), false);
+}
+
+/*
+ * Place the workqueue handler on the specified CPU if online, otherwise
+ * just run it whereever.  This is useful for placing workqueue handlers
+ * that are to invoke the specified CPU's callbacks.
+ */
+static bool srcu_queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
+				       struct delayed_work *dwork,
+				       unsigned long delay)
+{
+	bool ret;
+
+	preempt_disable();
+	if (READ_ONCE(per_cpu(srcu_online, cpu)))
+		ret = queue_delayed_work_on(cpu, wq, dwork, delay);
+	else
+		ret = queue_delayed_work(wq, dwork, delay);
+	preempt_enable();
+	return ret;
+}
+
+/*
+ * Schedule callback invocation for the specified srcu_data structure,
+ * if possible, on the corresponding CPU.
+ */
+static void srcu_schedule_cbs_sdp(struct srcu_data *sdp, unsigned long delay)
+{
+	srcu_queue_delayed_work_on(sdp->cpu, system_power_efficient_wq,
+				   &sdp->work, delay);
+}
+
+/*
+ * Schedule callback invocation for all srcu_data structures associated
+ * with the specified srcu_node structure, if possible, on the corresponding
+ * CPUs.
+ */
+static void srcu_schedule_cbs_snp(struct srcu_struct *sp, struct srcu_node *snp)
+{
+	int cpu;
+
+	for (cpu = snp->grplo; cpu <= snp->grphi; cpu++)
+		srcu_schedule_cbs_sdp(per_cpu_ptr(sp->sda, cpu), SRCU_INTERVAL);
+}
+
+/*
+ * Note the end of an SRCU grace period.  Initiates callback invocation
+ * and starts a new grace period if needed.
+ *
+ * The ->srcu_cb_mutex acquisition does not protect any data, but
+ * instead prevents more than one grace period from starting while we
+ * are initiating callback invocation.  This allows the ->srcu_have_cbs[]
+ * array to have a finite number of elements.
+ */
+static void srcu_gp_end(struct srcu_struct *sp)
+{
+	bool cbs;
+	unsigned long gpseq;
+	int idx;
+	int idxnext;
+	struct srcu_node *snp;
+
+	/* Prevent more than one additional grace period. */
+	mutex_lock(&sp->srcu_cb_mutex);
+
+	/* End the current grace period. */
+	spin_lock_irq(&sp->gp_lock);
+	idx = rcu_seq_state(sp->srcu_gp_seq);
+	WARN_ON_ONCE(idx != SRCU_STATE_SCAN2);
+	rcu_seq_end(&sp->srcu_gp_seq);
+	gpseq = rcu_seq_current(&sp->srcu_gp_seq);
+	spin_unlock_irq(&sp->gp_lock);
+	mutex_unlock(&sp->srcu_gp_mutex);
+	/* A new grace period can start at this point.  But only one. */
+
+	/* Initiate callback invocation as needed. */
+	idx = rcu_seq_ctr(gpseq) % ARRAY_SIZE(snp->srcu_have_cbs);
+	idxnext = (idx + 1) % ARRAY_SIZE(snp->srcu_have_cbs);
+	rcu_for_each_node_breadth_first(sp, snp) {
+		spin_lock_irq(&snp->lock);
+		cbs = false;
+		if (snp >= sp->level[rcu_num_lvls - 1])
+			cbs = snp->srcu_have_cbs[idx] == gpseq;
+		snp->srcu_have_cbs[idx] = gpseq;
+		rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1);
+		spin_unlock_irq(&snp->lock);
+		if (cbs) {
+			smp_mb(); /* GP end before CB invocation. */
+			srcu_schedule_cbs_snp(sp, snp);
+		}
+	}
+
+	/* Callback initiation done, allow grace periods after next. */
+	mutex_unlock(&sp->srcu_cb_mutex);
+
+	/* Start a new grace period if needed. */
+	spin_lock_irq(&sp->gp_lock);
+	gpseq = rcu_seq_current(&sp->srcu_gp_seq);
+	if (!rcu_seq_state(gpseq) &&
+	    ULONG_CMP_LT(gpseq, sp->srcu_gp_seq_needed)) {
+		srcu_gp_start(sp);
+		spin_unlock_irq(&sp->gp_lock);
+		/* Throttle expedited grace periods: Should be rare! */
+		srcu_reschedule(sp, atomic_read(&sp->srcu_exp_cnt) &&
+				    rcu_seq_ctr(gpseq) & 0xf
+				    ? 0
+				    : SRCU_INTERVAL);
+	} else {
+		spin_unlock_irq(&sp->gp_lock);
+	}
+}
+
+/*
+ * Funnel-locking scheme to scalably mediate many concurrent grace-period
+ * requests.  The winner has to do the work of actually starting grace
+ * period s.  Losers must either ensure that their desired grace-period
+ * number is recorded on at least their leaf srcu_node structure, or they
+ * must take steps to invoke their own callbacks.
+ */
+static void srcu_funnel_gp_start(struct srcu_struct *sp,
+				 struct srcu_data *sdp,
+				 unsigned long s)
+{
+	unsigned long flags;
+	int idx = rcu_seq_ctr(s) % ARRAY_SIZE(sdp->mynode->srcu_have_cbs);
+	struct srcu_node *snp = sdp->mynode;
+	unsigned long snp_seq;
+
+	/* Each pass through the loop does one level of the srcu_node tree. */
+	for (; snp != NULL; snp = snp->srcu_parent) {
+		if (rcu_seq_done(&sp->srcu_gp_seq, s) && snp != sdp->mynode)
+			return; /* GP already done and CBs recorded. */
+		spin_lock_irqsave(&snp->lock, flags);
+		if (ULONG_CMP_GE(snp->srcu_have_cbs[idx], s)) {
+			snp_seq = snp->srcu_have_cbs[idx];
+			spin_unlock_irqrestore(&snp->lock, flags);
+			if (snp == sdp->mynode && snp_seq != s) {
+				smp_mb(); /* CBs after GP! */
+				srcu_schedule_cbs_sdp(sdp, 0);
+			}
+			return;
+		}
+		snp->srcu_have_cbs[idx] = s;
+		spin_unlock_irqrestore(&snp->lock, flags);
+	}
+
+	/* Top of tree, must ensure the grace period will be started. */
+	spin_lock_irqsave(&sp->gp_lock, flags);
+	if (ULONG_CMP_LT(sp->srcu_gp_seq_needed, s)) {
+		/*
+		 * Record need for grace period s.  Pair with load
+		 * acquire setting up for initialization.
+		 */
+		smp_store_release(&sp->srcu_gp_seq_needed, s); /*^^^*/
+	}
+
+	/* If grace period not already done and none in progress, start it. */
+	if (!rcu_seq_done(&sp->srcu_gp_seq, s) &&
+	    rcu_seq_state(sp->srcu_gp_seq) == SRCU_STATE_IDLE) {
+		WARN_ON_ONCE(ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed));
+		srcu_gp_start(sp);
+		queue_delayed_work(system_power_efficient_wq, &sp->work,
+				   atomic_read(&sp->srcu_exp_cnt)
+				   ? 0
+				   : SRCU_INTERVAL);
+	}
+	spin_unlock_irqrestore(&sp->gp_lock, flags);
+}
+
+/*
  * Wait until all readers counted by array index idx complete, but
  * loop an additional time if there is an expedited grace period pending.
- * The caller must ensure that ->completed is not changed while checking.
+ * The caller must ensure that ->srcu_idx is not changed while checking.
  */
 static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
 {
@@ -277,13 +586,13 @@ static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
 }
 
 /*
- * Increment the ->completed counter so that future SRCU readers will
- * use the other rank of the ->(un)lock_count[] arrays.  This allows
+ * Increment the ->srcu_idx counter so that future SRCU readers will
+ * use the other rank of the ->srcu_(un)lock_count[] arrays.  This allows
  * us to wait for pre-existing readers in a starvation-free manner.
  */
 static void srcu_flip(struct srcu_struct *sp)
 {
-	WRITE_ONCE(sp->completed, sp->completed + 1);
+	WRITE_ONCE(sp->srcu_idx, sp->srcu_idx + 1);
 
 	/*
 	 * Ensure that if the updater misses an __srcu_read_unlock()
@@ -296,21 +605,9 @@ static void srcu_flip(struct srcu_struct *sp)
 }
 
 /*
- * End an SRCU grace period.
- */
-static void srcu_gp_end(struct srcu_struct *sp)
-{
-	rcu_seq_end(&sp->srcu_gp_seq);
-
-	spin_lock_irq(&sp->queue_lock);
-	rcu_segcblist_advance(&sp->srcu_cblist,
-			      rcu_seq_current(&sp->srcu_gp_seq));
-	spin_unlock_irq(&sp->queue_lock);
-}
-
-/*
- * Enqueue an SRCU callback on the specified srcu_struct structure,
- * initiating grace-period processing if it is not already running.
+ * Enqueue an SRCU callback on the srcu_data structure associated with
+ * the current CPU and the specified srcu_struct structure, initiating
+ * grace-period processing if it is not already running.
  *
  * Note that all CPUs must agree that the grace period extended beyond
  * all pre-existing SRCU read-side critical section.  On systems with
@@ -335,33 +632,40 @@ static void srcu_gp_end(struct srcu_struct *sp)
  * srcu_read_lock(), and srcu_read_unlock() that are all passed the same
  * srcu_struct structure.
  */
-void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
+void call_srcu(struct srcu_struct *sp, struct rcu_head *rhp,
 	       rcu_callback_t func)
 {
 	unsigned long flags;
-
-	head->next = NULL;
-	head->func = func;
-	spin_lock_irqsave(&sp->queue_lock, flags);
-	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
-	rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
-	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
-		srcu_gp_start(sp);
-		queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
+	bool needgp = false;
+	unsigned long s;
+	struct srcu_data *sdp;
+
+	check_init_srcu_struct(sp);
+	rhp->func = func;
+	local_irq_save(flags);
+	sdp = this_cpu_ptr(sp->sda);
+	spin_lock(&sdp->lock);
+	rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp, false);
+	rcu_segcblist_advance(&sdp->srcu_cblist,
+			      rcu_seq_current(&sp->srcu_gp_seq));
+	s = rcu_seq_snap(&sp->srcu_gp_seq);
+	(void)rcu_segcblist_accelerate(&sdp->srcu_cblist, s);
+	if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) {
+		sdp->srcu_gp_seq_needed = s;
+		needgp = true;
 	}
-	spin_unlock_irqrestore(&sp->queue_lock, flags);
+	spin_unlock_irqrestore(&sdp->lock, flags);
+	if (needgp)
+		srcu_funnel_gp_start(sp, sdp, s);
 }
 EXPORT_SYMBOL_GPL(call_srcu);
 
-static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay);
-
 /*
  * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
  */
 static void __synchronize_srcu(struct srcu_struct *sp)
 {
 	struct rcu_synchronize rcu;
-	struct rcu_head *head = &rcu.head;
 
 	RCU_LOCKDEP_WARN(lock_is_held(&sp->dep_map) ||
 			 lock_is_held(&rcu_bh_lock_map) ||
@@ -372,26 +676,12 @@ static void __synchronize_srcu(struct srcu_struct *sp)
 	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
 		return;
 	might_sleep();
+	check_init_srcu_struct(sp);
 	init_completion(&rcu.completion);
-
-	head->next = NULL;
-	head->func = wakeme_after_rcu;
-	spin_lock_irq(&sp->queue_lock);
-	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
-	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
-		/* steal the processing owner */
-		rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
-		srcu_gp_start(sp);
-		spin_unlock_irq(&sp->queue_lock);
-		/* give the processing owner to work_struct */
-		srcu_reschedule(sp, 0);
-	} else {
-		rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
-		spin_unlock_irq(&sp->queue_lock);
-	}
-
+	init_rcu_head_on_stack(&rcu.head);
+	call_srcu(sp, &rcu.head, wakeme_after_rcu);
 	wait_for_completion(&rcu.completion);
-	smp_mb(); /* Caller's later accesses after GP. */
+	destroy_rcu_head_on_stack(&rcu.head);
 }
 
 /**
@@ -426,8 +716,8 @@ EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
  *
  * Wait for the count to drain to zero of both indexes. To avoid the
  * possible starvation of synchronize_srcu(), it waits for the count of
- * the index=((->completed & 1) ^ 1) to drain to zero at first,
- * and then flip the completed and wait for the count of the other index.
+ * the index=((->srcu_idx & 1) ^ 1) to drain to zero at first,
+ * and then flip the srcu_idx and wait for the count of the other index.
  *
  * Can block; must be called from process context.
  *
@@ -468,13 +758,69 @@ void synchronize_srcu(struct srcu_struct *sp)
 }
 EXPORT_SYMBOL_GPL(synchronize_srcu);
 
+/*
+ * Callback function for srcu_barrier() use.
+ */
+static void srcu_barrier_cb(struct rcu_head *rhp)
+{
+	struct srcu_data *sdp;
+	struct srcu_struct *sp;
+
+	sdp = container_of(rhp, struct srcu_data, srcu_barrier_head);
+	sp = sdp->sp;
+	if (atomic_dec_and_test(&sp->srcu_barrier_cpu_cnt))
+		complete(&sp->srcu_barrier_completion);
+}
+
 /**
  * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
  * @sp: srcu_struct on which to wait for in-flight callbacks.
  */
 void srcu_barrier(struct srcu_struct *sp)
 {
-	synchronize_srcu(sp);
+	int cpu;
+	struct srcu_data *sdp;
+	unsigned long s = rcu_seq_snap(&sp->srcu_barrier_seq);
+
+	check_init_srcu_struct(sp);
+	mutex_lock(&sp->srcu_barrier_mutex);
+	if (rcu_seq_done(&sp->srcu_barrier_seq, s)) {
+		smp_mb(); /* Force ordering following return. */
+		mutex_unlock(&sp->srcu_barrier_mutex);
+		return; /* Someone else did our work for us. */
+	}
+	rcu_seq_start(&sp->srcu_barrier_seq);
+	init_completion(&sp->srcu_barrier_completion);
+
+	/* Initial count prevents reaching zero until all CBs are posted. */
+	atomic_set(&sp->srcu_barrier_cpu_cnt, 1);
+
+	/*
+	 * Each pass through this loop enqueues a callback, but only
+	 * on CPUs already having callbacks enqueued.  Note that if
+	 * a CPU already has callbacks enqueue, it must have already
+	 * registered the need for a future grace period, so all we
+	 * need do is enqueue a callback that will use the same
+	 * grace period as the last callback already in the queue.
+	 */
+	for_each_possible_cpu(cpu) {
+		sdp = per_cpu_ptr(sp->sda, cpu);
+		spin_lock_irq(&sdp->lock);
+		atomic_inc(&sp->srcu_barrier_cpu_cnt);
+		sdp->srcu_barrier_head.func = srcu_barrier_cb;
+		if (!rcu_segcblist_entrain(&sdp->srcu_cblist,
+					   &sdp->srcu_barrier_head, 0))
+			atomic_dec(&sp->srcu_barrier_cpu_cnt);
+		spin_unlock_irq(&sdp->lock);
+	}
+
+	/* Remove the initial count, at which point reaching zero can happen. */
+	if (atomic_dec_and_test(&sp->srcu_barrier_cpu_cnt))
+		complete(&sp->srcu_barrier_completion);
+	wait_for_completion(&sp->srcu_barrier_completion);
+
+	rcu_seq_end(&sp->srcu_barrier_seq);
+	mutex_unlock(&sp->srcu_barrier_mutex);
 }
 EXPORT_SYMBOL_GPL(srcu_barrier);
 
@@ -487,21 +833,24 @@ EXPORT_SYMBOL_GPL(srcu_barrier);
  */
 unsigned long srcu_batches_completed(struct srcu_struct *sp)
 {
-	return sp->completed;
+	return sp->srcu_idx;
 }
 EXPORT_SYMBOL_GPL(srcu_batches_completed);
 
 /*
- * Core SRCU state machine.  Advance callbacks from ->batch_check0 to
- * ->batch_check1 and then to ->batch_done as readers drain.
+ * Core SRCU state machine.  Push state bits of ->srcu_gp_seq
+ * to SRCU_STATE_SCAN2, and invoke srcu_gp_end() when scan has
+ * completed in that state.
  */
-static void srcu_advance_batches(struct srcu_struct *sp)
+static void srcu_advance_state(struct srcu_struct *sp)
 {
 	int idx;
 
+	mutex_lock(&sp->srcu_gp_mutex);
+
 	/*
 	 * Because readers might be delayed for an extended period after
-	 * fetching ->completed for their index, at any point in time there
+	 * fetching ->srcu_idx for their index, at any point in time there
 	 * might well be readers using both idx=0 and idx=1.  We therefore
 	 * need to wait for readers to clear from both index values before
 	 * invoking a callback.
@@ -511,23 +860,29 @@ static void srcu_advance_batches(struct srcu_struct *sp)
 	 */
 	idx = rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq)); /* ^^^ */
 	if (idx == SRCU_STATE_IDLE) {
-		spin_lock_irq(&sp->queue_lock);
-		if (rcu_segcblist_empty(&sp->srcu_cblist)) {
-			spin_unlock_irq(&sp->queue_lock);
+		spin_lock_irq(&sp->gp_lock);
+		if (ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed)) {
+			WARN_ON_ONCE(rcu_seq_state(sp->srcu_gp_seq));
+			spin_unlock_irq(&sp->gp_lock);
+			mutex_unlock(&sp->srcu_gp_mutex);
 			return;
 		}
 		idx = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
 		if (idx == SRCU_STATE_IDLE)
 			srcu_gp_start(sp);
-		spin_unlock_irq(&sp->queue_lock);
-		if (idx != SRCU_STATE_IDLE)
+		spin_unlock_irq(&sp->gp_lock);
+		if (idx != SRCU_STATE_IDLE) {
+			mutex_unlock(&sp->srcu_gp_mutex);
 			return; /* Someone else started the grace period. */
+		}
 	}
 
 	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
-		idx = 1 ^ (sp->completed & 1);
-		if (!try_check_zero(sp, idx, 1))
+		idx = 1 ^ (sp->srcu_idx & 1);
+		if (!try_check_zero(sp, idx, 1)) {
+			mutex_unlock(&sp->srcu_gp_mutex);
 			return; /* readers present, retry later. */
+		}
 		srcu_flip(sp);
 		rcu_seq_set_state(&sp->srcu_gp_seq, SRCU_STATE_SCAN2);
 	}
@@ -538,10 +893,12 @@ static void srcu_advance_batches(struct srcu_struct *sp)
 		 * SRCU read-side critical sections are normally short,
 		 * so check at least twice in quick succession after a flip.
 		 */
-		idx = 1 ^ (sp->completed & 1);
-		if (!try_check_zero(sp, idx, 2))
-			return; /* readers present, retry after later. */
-		srcu_gp_end(sp);
+		idx = 1 ^ (sp->srcu_idx & 1);
+		if (!try_check_zero(sp, idx, 2)) {
+			mutex_unlock(&sp->srcu_gp_mutex);
+			return; /* readers present, retry later. */
+		}
+		srcu_gp_end(sp);  /* Releases ->srcu_gp_mutex. */
 	}
 }
 
@@ -551,28 +908,51 @@ static void srcu_advance_batches(struct srcu_struct *sp)
  * the workqueue.  Note that needed memory barriers have been executed
  * in this task's context by srcu_readers_active_idx_check().
  */
-static void srcu_invoke_callbacks(struct srcu_struct *sp)
+static void srcu_invoke_callbacks(struct work_struct *work)
 {
+	bool more;
 	struct rcu_cblist ready_cbs;
 	struct rcu_head *rhp;
+	struct srcu_data *sdp;
+	struct srcu_struct *sp;
 
-	spin_lock_irq(&sp->queue_lock);
-	if (!rcu_segcblist_ready_cbs(&sp->srcu_cblist)) {
-		spin_unlock_irq(&sp->queue_lock);
-		return;
-	}
+	sdp = container_of(work, struct srcu_data, work.work);
+	sp = sdp->sp;
 	rcu_cblist_init(&ready_cbs);
-	rcu_segcblist_extract_done_cbs(&sp->srcu_cblist, &ready_cbs);
-	spin_unlock_irq(&sp->queue_lock);
+	spin_lock_irq(&sdp->lock);
+	smp_mb(); /* Old grace periods before callback invocation! */
+	rcu_segcblist_advance(&sdp->srcu_cblist,
+			      rcu_seq_current(&sp->srcu_gp_seq));
+	if (sdp->srcu_cblist_invoking ||
+	    !rcu_segcblist_ready_cbs(&sdp->srcu_cblist)) {
+		spin_unlock_irq(&sdp->lock);
+		return;  /* Someone else on the job or nothing to do. */
+	}
+
+	/* We are on the job!  Extract and invoke ready callbacks. */
+	sdp->srcu_cblist_invoking = true;
+	rcu_segcblist_extract_done_cbs(&sdp->srcu_cblist, &ready_cbs);
+	spin_unlock_irq(&sdp->lock);
 	rhp = rcu_cblist_dequeue(&ready_cbs);
 	for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
 		local_bh_disable();
 		rhp->func(rhp);
 		local_bh_enable();
 	}
-	spin_lock_irq(&sp->queue_lock);
-	rcu_segcblist_insert_count(&sp->srcu_cblist, &ready_cbs);
-	spin_unlock_irq(&sp->queue_lock);
+
+	/*
+	 * Update counts, accelerate new callbacks, and if needed,
+	 * schedule another round of callback invocation.
+	 */
+	spin_lock_irq(&sdp->lock);
+	rcu_segcblist_insert_count(&sdp->srcu_cblist, &ready_cbs);
+	(void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
+				       rcu_seq_snap(&sp->srcu_gp_seq));
+	sdp->srcu_cblist_invoking = false;
+	more = rcu_segcblist_ready_cbs(&sdp->srcu_cblist);
+	spin_unlock_irq(&sdp->lock);
+	if (more)
+		srcu_schedule_cbs_sdp(sdp, 0);
 }
 
 /*
@@ -581,19 +961,21 @@ static void srcu_invoke_callbacks(struct srcu_struct *sp)
  */
 static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
 {
-	bool pending = true;
-	int state;
+	bool pushgp = true;
 
-	if (rcu_segcblist_empty(&sp->srcu_cblist)) {
-		spin_lock_irq(&sp->queue_lock);
-		state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
-		if (rcu_segcblist_empty(&sp->srcu_cblist) &&
-		    state == SRCU_STATE_IDLE)
-			pending = false;
-		spin_unlock_irq(&sp->queue_lock);
+	spin_lock_irq(&sp->gp_lock);
+	if (ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed)) {
+		if (!WARN_ON_ONCE(rcu_seq_state(sp->srcu_gp_seq))) {
+			/* All requests fulfilled, time to go idle. */
+			pushgp = false;
+		}
+	} else if (!rcu_seq_state(sp->srcu_gp_seq)) {
+		/* Outstanding request and no GP.  Start one. */
+		srcu_gp_start(sp);
 	}
+	spin_unlock_irq(&sp->gp_lock);
 
-	if (pending)
+	if (pushgp)
 		queue_delayed_work(system_power_efficient_wq, &sp->work, delay);
 }
 
@@ -606,8 +988,7 @@ void process_srcu(struct work_struct *work)
 
 	sp = container_of(work, struct srcu_struct, work.work);
 
-	srcu_advance_batches(sp);
-	srcu_invoke_callbacks(sp);
+	srcu_advance_state(sp);
 	srcu_reschedule(sp, atomic_read(&sp->srcu_exp_cnt) ? 0 : SRCU_INTERVAL);
 }
 EXPORT_SYMBOL_GPL(process_srcu);
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index e0eb798181bc..75ca946734e6 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3783,12 +3783,16 @@ int rcutree_online_cpu(unsigned int cpu)
 {
 	sync_sched_exp_online_cleanup(cpu);
 	rcutree_affinity_setting(cpu, -1);
+	if (IS_ENABLED(CONFIG_TREE_SRCU))
+		srcu_online_cpu(cpu);
 	return 0;
 }
 
 int rcutree_offline_cpu(unsigned int cpu)
 {
 	rcutree_affinity_setting(cpu, cpu);
+	if (IS_ENABLED(CONFIG_TREE_SRCU))
+		srcu_offline_cpu(cpu);
 	return 0;
 }
 
@@ -4164,6 +4168,8 @@ void __init rcu_init(void)
 	for_each_online_cpu(cpu) {
 		rcutree_prepare_cpu(cpu);
 		rcu_cpu_starting(cpu);
+		if (IS_ENABLED(CONFIG_TREE_SRCU))
+			srcu_online_cpu(cpu);
 	}
 }
 
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index a2a45cb629d6..0e598ab08fea 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -541,6 +541,14 @@ static bool rcu_nohz_full_cpu(struct rcu_state *rsp);
 static void rcu_dynticks_task_enter(void);
 static void rcu_dynticks_task_exit(void);
 
+#ifdef CONFIG_SRCU
+void srcu_online_cpu(unsigned int cpu);
+void srcu_offline_cpu(unsigned int cpu);
+#else /* #ifdef CONFIG_SRCU */
+void srcu_online_cpu(unsigned int cpu) { }
+void srcu_offline_cpu(unsigned int cpu) { }
+#endif /* #else #ifdef CONFIG_SRCU */
+
 #endif /* #ifndef RCU_TREE_NONCORE */
 
 #ifdef CONFIG_RCU_TRACE
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* Re: [PATCH tip/core/rcu 01/40] rcu: Maintain special bits at bottom of ->dynticks counter
  2017-04-12 17:39 ` [PATCH tip/core/rcu 01/40] rcu: Maintain special bits at bottom of ->dynticks counter Paul E. McKenney
@ 2017-04-13  9:20   ` Peter Zijlstra
  2017-04-13 16:15     ` Paul E. McKenney
  0 siblings, 1 reply; 176+ messages in thread
From: Peter Zijlstra @ 2017-04-13  9:20 UTC (permalink / raw)
  To: Paul E. McKenney
  Cc: linux-kernel, mingo, jiangshanlai, dipankar, akpm,
	mathieu.desnoyers, josh, tglx, rostedt, dhowells, edumazet,
	fweisbec, oleg, bobby.prani

On Wed, Apr 12, 2017 at 10:39:46AM -0700, Paul E. McKenney wrote:
> Currently, IPIs are used to force other CPUs to invalidate their TLBs
> in response to a kernel virtual-memory mapping change.  This works, but
> degrades both battery lifetime (for idle CPUs) and real-time response
> (for nohz_full CPUs), and in addition results in unnecessary IPIs due to
> the fact that CPUs executing in usermode are unaffected by stale kernel
> mappings.  It would be better to cause a CPU executing in usermode to
> wait until it is entering kernel mode to do the flush, first to avoid
> interrupting usemode tasks and second to handle multiple flush requests
> with a single flush in the case of a long-running user task.
> 
> This commit therefore reserves a bit at the bottom of the ->dynticks
> counter, which is checked upon exit from extended quiescent states.
> If it is set, it is cleared and then a new rcu_eqs_special_exit() macro is
> invoked, which, if not supplied, is an empty single-pass do-while loop.
> If this bottom bit is set on -entry- to an extended quiescent state,
> then a WARN_ON_ONCE() triggers.
> 
> This bottom bit may be set using a new rcu_eqs_special_set() function,
> which returns true if the bit was set, or false if the CPU turned
> out to not be in an extended quiescent state.  Please note that this
> function refuses to set the bit for a non-nohz_full CPU when that CPU
> is executing in usermode because usermode execution is tracked by RCU
> as a dyntick-idle extended quiescent state only for nohz_full CPUs.
> 
> Reported-by: Andy Lutomirski <luto@amacapital.net>

Isn't that more a: Requested-by ?

^ permalink raw reply	[flat|nested] 176+ messages in thread

* Re: [PATCH tip/core/rcu 02/40] rcu: Make arch select smp_mb__after_unlock_lock() strength
  2017-04-12 17:39 ` [PATCH tip/core/rcu 02/40] rcu: Make arch select smp_mb__after_unlock_lock() strength Paul E. McKenney
@ 2017-04-13  9:21   ` Peter Zijlstra
  2017-04-13 16:17     ` Paul E. McKenney
  2017-04-13  9:24   ` Peter Zijlstra
  1 sibling, 1 reply; 176+ messages in thread
From: Peter Zijlstra @ 2017-04-13  9:21 UTC (permalink / raw)
  To: Paul E. McKenney
  Cc: linux-kernel, mingo, jiangshanlai, dipankar, akpm,
	mathieu.desnoyers, josh, tglx, rostedt, dhowells, edumazet,
	fweisbec, oleg, bobby.prani, Will Deacon, Boqun Feng,
	Benjamin Herrenschmidt, Paul Mackerras, linuxppc-dev

On Wed, Apr 12, 2017 at 10:39:47AM -0700, Paul E. McKenney wrote:

> CONFIG_ARCH_WEAK_RELACQ Kconfig option.

Naming in the changelog and patch don't match.

> +config ARCH_WEAK_RELEASE_ACQUIRE
> +	bool
> +

^ permalink raw reply	[flat|nested] 176+ messages in thread

* Re: [PATCH tip/core/rcu 02/40] rcu: Make arch select smp_mb__after_unlock_lock() strength
  2017-04-12 17:39 ` [PATCH tip/core/rcu 02/40] rcu: Make arch select smp_mb__after_unlock_lock() strength Paul E. McKenney
  2017-04-13  9:21   ` Peter Zijlstra
@ 2017-04-13  9:24   ` Peter Zijlstra
  2017-04-13 16:26     ` Paul E. McKenney
  1 sibling, 1 reply; 176+ messages in thread
From: Peter Zijlstra @ 2017-04-13  9:24 UTC (permalink / raw)
  To: Paul E. McKenney
  Cc: linux-kernel, mingo, jiangshanlai, dipankar, akpm,
	mathieu.desnoyers, josh, tglx, rostedt, dhowells, edumazet,
	fweisbec, oleg, bobby.prani, Will Deacon, Boqun Feng,
	Benjamin Herrenschmidt, Paul Mackerras, linuxppc-dev

On Wed, Apr 12, 2017 at 10:39:47AM -0700, Paul E. McKenney wrote:
> The definition of smp_mb__after_unlock_lock() is currently smp_mb()
> for CONFIG_PPC and a no-op otherwise.  It would be better to instead
> provide an architecture-selectable Kconfig option, and select the
> strength of smp_mb__after_unlock_lock() based on that option. 


Why is this better? Do we want to have more of this? I thought we still
wanted to convince PPC to go RCsc and eradicate all this RCpc 'fun'. But
instead now you're making it look like its OK to grow more of this pain.

^ permalink raw reply	[flat|nested] 176+ messages in thread

* Re: [PATCH tip/core/rcu 37/40] srcu: Create a tiny SRCU
  2017-04-12 17:40 ` [PATCH tip/core/rcu 37/40] srcu: Create a tiny SRCU Paul E. McKenney
@ 2017-04-13  9:48   ` Peter Zijlstra
  2017-04-13 16:30     ` Paul E. McKenney
  0 siblings, 1 reply; 176+ messages in thread
From: Peter Zijlstra @ 2017-04-13  9:48 UTC (permalink / raw)
  To: Paul E. McKenney
  Cc: linux-kernel, mingo, jiangshanlai, dipankar, akpm,
	mathieu.desnoyers, josh, tglx, rostedt, dhowells, edumazet,
	fweisbec, oleg, bobby.prani

On Wed, Apr 12, 2017 at 10:40:22AM -0700, Paul E. McKenney wrote:
> In response to automated complaints about modifications to SRCU
> increasing its size, this commit creates a tiny SRCU that is
> used in SMP=y && PREEMPT=n builds.

You mean SMP=n && PREEMPT=n, right?

config TINY_RCU
        bool
        default y if !PREEMPT && !SMP

> +config TINY_SRCU
> +	bool
> +	default y if TINY_RCU
> +	help
> +	  This option selects the single-CPU non-preemptible version of SRCU.

^ permalink raw reply	[flat|nested] 176+ messages in thread

* Re: [PATCH tip/core/rcu 40/40] srcu: Parallelize callback handling
  2017-04-12 17:40 ` [PATCH tip/core/rcu 40/40] srcu: Parallelize callback handling Paul E. McKenney
@ 2017-04-13  9:50   ` Peter Zijlstra
  2017-04-13 16:37     ` Paul E. McKenney
  2017-04-13  9:54   ` Peter Zijlstra
  2017-04-20  3:40   ` powerpc KVM build break in linux-next (was Re: [PATCH tip/core/rcu 40/40] srcu: Parallelize callback handling) Michael Ellerman
  2 siblings, 1 reply; 176+ messages in thread
From: Peter Zijlstra @ 2017-04-13  9:50 UTC (permalink / raw)
  To: Paul E. McKenney
  Cc: linux-kernel, mingo, jiangshanlai, dipankar, akpm,
	mathieu.desnoyers, josh, tglx, rostedt, dhowells, edumazet,
	fweisbec, oleg, bobby.prani

On Wed, Apr 12, 2017 at 10:40:25AM -0700, Paul E. McKenney wrote:
> Peter Zijlstra proposed using SRCU to reduce mmap_sem contention [1],

Bugger, now you're making me feel bad for not having updated those
patches in ages.. I'll try and bump it on the todo list.

^ permalink raw reply	[flat|nested] 176+ messages in thread

* Re: [PATCH tip/core/rcu 40/40] srcu: Parallelize callback handling
  2017-04-12 17:40 ` [PATCH tip/core/rcu 40/40] srcu: Parallelize callback handling Paul E. McKenney
  2017-04-13  9:50   ` Peter Zijlstra
@ 2017-04-13  9:54   ` Peter Zijlstra
  2017-04-13 16:50     ` Paul E. McKenney
  2017-04-20  3:40   ` powerpc KVM build break in linux-next (was Re: [PATCH tip/core/rcu 40/40] srcu: Parallelize callback handling) Michael Ellerman
  2 siblings, 1 reply; 176+ messages in thread
From: Peter Zijlstra @ 2017-04-13  9:54 UTC (permalink / raw)
  To: Paul E. McKenney
  Cc: linux-kernel, mingo, jiangshanlai, dipankar, akpm,
	mathieu.desnoyers, josh, tglx, rostedt, dhowells, edumazet,
	fweisbec, oleg, bobby.prani

On Wed, Apr 12, 2017 at 10:40:25AM -0700, Paul E. McKenney wrote:
> Peter Zijlstra proposed using SRCU to reduce mmap_sem contention [1],
> however, there are workloads that could result in a high volume of
> concurrent invocations of call_srcu(), which with current SRCU would
> result in excessive lock contention on the srcu_struct structure's
> ->queue_lock, which protects SRCU's callback lists.  This commit therefore
> moves SRCU to per-CPU callback lists, thus greatly reducing contention.
> 
> Because a given SRCU instance no longer has a single centralized callback
> list, starting grace periods and invoking callbacks each require a bit
> more work.  These are handled using an srcu_node tree that is in some ways
> similar to the rcu_node trees used by RCU-bh, RCU-preempt, and RCU-sched
> (for example, the srcu_node tree shape is controlled by exactly the
> same Kconfig options and boot parameters that control the shape of the
> rcu_node tree).
> 
> In addition, the old per-CPU srcu_array structure is now named srcu_data
> and contains an rcu_segcblist structure named ->srcu_cblist for its
> callbacks (and a spinlock to protect this).  The srcu_struct gets
> an srcu_gp_seq that is used to associate callback segments with the
> corresponding completion-time grace-period number.  These completion-time
> grace-period numbers are propagated up the srcu_node tree so that the
> grace-period workqueue handler can determine whether additional grace
> periods are needed on the one hand and where to look for callbacks that
> are ready to be invoked.
> 
> The srcu_barrier() function must now wait on all instances of the
> per-CPU ->srcu_cblist.  Because each ->srcu_cblist is protected
> by ->lock, srcu_barrier() can remotely add the needed callbacks.
> In theory, it could also remotely start grace periods, but this gets
> complex and racy.  And interestingly enough, it is never necessary to
> start a grace period in this case because srcu_barrier() only enqueues
> a callback when a callback is already present.  And a grace period has
> to have already been started for this pre-existing callback.  And it is
> only the callback that srcu_barrier() needs to wait on, not any particular
> grace period.  Therefore, a new rcu_segcblist_entrain() function enqueues
> the srcu_barrier() function's callback into the same segment occupied by
> the pre-existing callback.  The special case where all the pre-existing
> callbacks are on a different list being invoked is handled by enqueuing
> srcu_barrier()'s callback into the RCU_DONE_TAIL segment, relying on
> the done-callbacks check that takes place after all callbacks are inovked.
> 
> Note that the readers use the same algorithm as before.  Note that there
> is a separate srcu_idx that tells the readers what counter to increment.
> This unfortunately cannot be combined with srcu_gp_seq because they
> need to be incremented at different times.

So one thing I've asked before I think, would it not be possible to
abstract PREEMPT_RCU and use the exact same code for PREEMPT_RCU and
SRCU ?

^ permalink raw reply	[flat|nested] 176+ messages in thread

* Re: [PATCH tip/core/rcu 01/40] rcu: Maintain special bits at bottom of ->dynticks counter
  2017-04-13  9:20   ` Peter Zijlstra
@ 2017-04-13 16:15     ` Paul E. McKenney
  0 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-13 16:15 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: linux-kernel, mingo, jiangshanlai, dipankar, akpm,
	mathieu.desnoyers, josh, tglx, rostedt, dhowells, edumazet,
	fweisbec, oleg, bobby.prani

On Thu, Apr 13, 2017 at 11:20:44AM +0200, Peter Zijlstra wrote:
> On Wed, Apr 12, 2017 at 10:39:46AM -0700, Paul E. McKenney wrote:
> > Currently, IPIs are used to force other CPUs to invalidate their TLBs
> > in response to a kernel virtual-memory mapping change.  This works, but
> > degrades both battery lifetime (for idle CPUs) and real-time response
> > (for nohz_full CPUs), and in addition results in unnecessary IPIs due to
> > the fact that CPUs executing in usermode are unaffected by stale kernel
> > mappings.  It would be better to cause a CPU executing in usermode to
> > wait until it is entering kernel mode to do the flush, first to avoid
> > interrupting usemode tasks and second to handle multiple flush requests
> > with a single flush in the case of a long-running user task.
> > 
> > This commit therefore reserves a bit at the bottom of the ->dynticks
> > counter, which is checked upon exit from extended quiescent states.
> > If it is set, it is cleared and then a new rcu_eqs_special_exit() macro is
> > invoked, which, if not supplied, is an empty single-pass do-while loop.
> > If this bottom bit is set on -entry- to an extended quiescent state,
> > then a WARN_ON_ONCE() triggers.
> > 
> > This bottom bit may be set using a new rcu_eqs_special_set() function,
> > which returns true if the bit was set, or false if the CPU turned
> > out to not be in an extended quiescent state.  Please note that this
> > function refuses to set the bit for a non-nohz_full CPU when that CPU
> > is executing in usermode because usermode execution is tracked by RCU
> > as a dyntick-idle extended quiescent state only for nohz_full CPUs.
> > 
> > Reported-by: Andy Lutomirski <luto@amacapital.net>
> 
> Isn't that more a: Requested-by ?

I am not too worried about the distinction.  Request a feature, report
the lack of a needed feature, or report a bug, but either way I had to
write the code.  ;-)

								Thanx, Paul

^ permalink raw reply	[flat|nested] 176+ messages in thread

* Re: [PATCH tip/core/rcu 02/40] rcu: Make arch select smp_mb__after_unlock_lock() strength
  2017-04-13  9:21   ` Peter Zijlstra
@ 2017-04-13 16:17     ` Paul E. McKenney
  0 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-13 16:17 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: linux-kernel, mingo, jiangshanlai, dipankar, akpm,
	mathieu.desnoyers, josh, tglx, rostedt, dhowells, edumazet,
	fweisbec, oleg, bobby.prani, Will Deacon, Boqun Feng,
	Benjamin Herrenschmidt, Paul Mackerras, linuxppc-dev

On Thu, Apr 13, 2017 at 11:21:53AM +0200, Peter Zijlstra wrote:
> On Wed, Apr 12, 2017 at 10:39:47AM -0700, Paul E. McKenney wrote:
> 
> > CONFIG_ARCH_WEAK_RELACQ Kconfig option.
> 
> Naming in the changelog and patch don't match.

Good eyes!  Fixed.

							Thanx, Paul

> > +config ARCH_WEAK_RELEASE_ACQUIRE
> > +	bool
> > +
> 
> 

^ permalink raw reply	[flat|nested] 176+ messages in thread

* Re: [PATCH tip/core/rcu 02/40] rcu: Make arch select smp_mb__after_unlock_lock() strength
  2017-04-13  9:24   ` Peter Zijlstra
@ 2017-04-13 16:26     ` Paul E. McKenney
  2017-04-13 16:37       ` Peter Zijlstra
  0 siblings, 1 reply; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-13 16:26 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: linux-kernel, mingo, jiangshanlai, dipankar, akpm,
	mathieu.desnoyers, josh, tglx, rostedt, dhowells, edumazet,
	fweisbec, oleg, bobby.prani, Will Deacon, Boqun Feng,
	Benjamin Herrenschmidt, Paul Mackerras, linuxppc-dev

On Thu, Apr 13, 2017 at 11:24:18AM +0200, Peter Zijlstra wrote:
> On Wed, Apr 12, 2017 at 10:39:47AM -0700, Paul E. McKenney wrote:
> > The definition of smp_mb__after_unlock_lock() is currently smp_mb()
> > for CONFIG_PPC and a no-op otherwise.  It would be better to instead
> > provide an architecture-selectable Kconfig option, and select the
> > strength of smp_mb__after_unlock_lock() based on that option. 
> 
> Why is this better? Do we want to have more of this? I thought we still
> wanted to convince PPC to go RCsc and eradicate all this RCpc 'fun'. But
> instead now you're making it look like its OK to grow more of this pain.

ARCH_WEAK_RELEASE_ACQUIRE actually works both ways.

To see this, imagine some strange alternate universe in which the Power
hardware guys actually did decide to switch PPC to doing RCsc as you
suggest.  There would still be a lot of Power hardware out there that
still does RCpc.  Therefore, powerpc builds that needed to run on old
Power hardware would select ARCH_WEAK_RELEASE_ACQUIRE, while kernels
built to run only on the shiny new (but mythical) alternate-universe
Power hardware would avoid selecting this Kconfig option.

But the real reason I queued this patch is that Ingo asked me for it:
https://lkml.org/lkml/2017/1/14/88

							Thanx, Paul

^ permalink raw reply	[flat|nested] 176+ messages in thread

* Re: [PATCH tip/core/rcu 37/40] srcu: Create a tiny SRCU
  2017-04-13  9:48   ` Peter Zijlstra
@ 2017-04-13 16:30     ` Paul E. McKenney
  0 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-13 16:30 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: linux-kernel, mingo, jiangshanlai, dipankar, akpm,
	mathieu.desnoyers, josh, tglx, rostedt, dhowells, edumazet,
	fweisbec, oleg, bobby.prani

On Thu, Apr 13, 2017 at 11:48:30AM +0200, Peter Zijlstra wrote:
> On Wed, Apr 12, 2017 at 10:40:22AM -0700, Paul E. McKenney wrote:
> > In response to automated complaints about modifications to SRCU
> > increasing its size, this commit creates a tiny SRCU that is
> > used in SMP=y && PREEMPT=n builds.
> 
> You mean SMP=n && PREEMPT=n, right?

I do, thank you for spotting this!  Fixed.

							Thanx, Paul

> config TINY_RCU
>         bool
>         default y if !PREEMPT && !SMP
> 
> > +config TINY_SRCU
> > +	bool
> > +	default y if TINY_RCU
> > +	help
> > +	  This option selects the single-CPU non-preemptible version of SRCU.
> 

^ permalink raw reply	[flat|nested] 176+ messages in thread

* Re: [PATCH tip/core/rcu 40/40] srcu: Parallelize callback handling
  2017-04-13  9:50   ` Peter Zijlstra
@ 2017-04-13 16:37     ` Paul E. McKenney
  2017-04-13 17:42       ` Paul E. McKenney
  0 siblings, 1 reply; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-13 16:37 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: linux-kernel, mingo, jiangshanlai, dipankar, akpm,
	mathieu.desnoyers, josh, tglx, rostedt, dhowells, edumazet,
	fweisbec, oleg, bobby.prani

On Thu, Apr 13, 2017 at 11:50:29AM +0200, Peter Zijlstra wrote:
> On Wed, Apr 12, 2017 at 10:40:25AM -0700, Paul E. McKenney wrote:
> > Peter Zijlstra proposed using SRCU to reduce mmap_sem contention [1],
> 
> Bugger, now you're making me feel bad for not having updated those
> patches in ages.. I'll try and bump it on the todo list.

Apologies, I wasn't trying to make you feel bad.  But I did get an old
version of the patch.  A much more recent one is here, which I have
added to the commit log:

	https://patchwork.kernel.org/patch/5108281/

For my part, I feel bad that I didn't realize much earlier that parallel
SRCU callbacks were needed.  As it was, someone had to tell me late
last year.

But yes, it would be really cool to have lockless VMA lookup!!!

							Thanx, Paul

^ permalink raw reply	[flat|nested] 176+ messages in thread

* Re: [PATCH tip/core/rcu 02/40] rcu: Make arch select smp_mb__after_unlock_lock() strength
  2017-04-13 16:26     ` Paul E. McKenney
@ 2017-04-13 16:37       ` Peter Zijlstra
  2017-04-13 17:03         ` Paul E. McKenney
  0 siblings, 1 reply; 176+ messages in thread
From: Peter Zijlstra @ 2017-04-13 16:37 UTC (permalink / raw)
  To: Paul E. McKenney
  Cc: linux-kernel, mingo, jiangshanlai, dipankar, akpm,
	mathieu.desnoyers, josh, tglx, rostedt, dhowells, edumazet,
	fweisbec, oleg, bobby.prani, Will Deacon, Boqun Feng,
	Benjamin Herrenschmidt, Paul Mackerras, linuxppc-dev

On Thu, Apr 13, 2017 at 09:26:51AM -0700, Paul E. McKenney wrote:

> ARCH_WEAK_RELEASE_ACQUIRE actually works both ways.
> 
> To see this, imagine some strange alternate universe in which the Power
> hardware guys actually did decide to switch PPC to doing RCsc as you
> suggest.  There would still be a lot of Power hardware out there that
> still does RCpc.  Therefore, powerpc builds that needed to run on old
> Power hardware would select ARCH_WEAK_RELEASE_ACQUIRE, while kernels
> built to run only on the shiny new (but mythical) alternate-universe
> Power hardware would avoid selecting this Kconfig option.

Ah, but Power software guys could do it today by replacing an LWSYNC
with a SYNC in say arch_spin_unlock().

And yes, I know this isn't a popular suggestion, but it would do the
trick.

Its just that since there's one (PPC) we can sort of pressure them with
the pain of being the only ones to hit all the bugs. But the moment more
appear (and I'm afraid it'll be MIPS, with the excuse that PPC already
does this) it will be ever so much harder to get rid of it.

Then again, maybe I should just give up and accept the Linux kernel has
RCpc locks..

^ permalink raw reply	[flat|nested] 176+ messages in thread

* Re: [PATCH tip/core/rcu 40/40] srcu: Parallelize callback handling
  2017-04-13  9:54   ` Peter Zijlstra
@ 2017-04-13 16:50     ` Paul E. McKenney
  0 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-13 16:50 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: linux-kernel, mingo, jiangshanlai, dipankar, akpm,
	mathieu.desnoyers, josh, tglx, rostedt, dhowells, edumazet,
	fweisbec, oleg, bobby.prani

On Thu, Apr 13, 2017 at 11:54:20AM +0200, Peter Zijlstra wrote:
> On Wed, Apr 12, 2017 at 10:40:25AM -0700, Paul E. McKenney wrote:
> > Peter Zijlstra proposed using SRCU to reduce mmap_sem contention [1],
> > however, there are workloads that could result in a high volume of
> > concurrent invocations of call_srcu(), which with current SRCU would
> > result in excessive lock contention on the srcu_struct structure's
> > ->queue_lock, which protects SRCU's callback lists.  This commit therefore
> > moves SRCU to per-CPU callback lists, thus greatly reducing contention.
> > 
> > Because a given SRCU instance no longer has a single centralized callback
> > list, starting grace periods and invoking callbacks each require a bit
> > more work.  These are handled using an srcu_node tree that is in some ways
> > similar to the rcu_node trees used by RCU-bh, RCU-preempt, and RCU-sched
> > (for example, the srcu_node tree shape is controlled by exactly the
> > same Kconfig options and boot parameters that control the shape of the
> > rcu_node tree).
> > 
> > In addition, the old per-CPU srcu_array structure is now named srcu_data
> > and contains an rcu_segcblist structure named ->srcu_cblist for its
> > callbacks (and a spinlock to protect this).  The srcu_struct gets
> > an srcu_gp_seq that is used to associate callback segments with the
> > corresponding completion-time grace-period number.  These completion-time
> > grace-period numbers are propagated up the srcu_node tree so that the
> > grace-period workqueue handler can determine whether additional grace
> > periods are needed on the one hand and where to look for callbacks that
> > are ready to be invoked.
> > 
> > The srcu_barrier() function must now wait on all instances of the
> > per-CPU ->srcu_cblist.  Because each ->srcu_cblist is protected
> > by ->lock, srcu_barrier() can remotely add the needed callbacks.
> > In theory, it could also remotely start grace periods, but this gets
> > complex and racy.  And interestingly enough, it is never necessary to
> > start a grace period in this case because srcu_barrier() only enqueues
> > a callback when a callback is already present.  And a grace period has
> > to have already been started for this pre-existing callback.  And it is
> > only the callback that srcu_barrier() needs to wait on, not any particular
> > grace period.  Therefore, a new rcu_segcblist_entrain() function enqueues
> > the srcu_barrier() function's callback into the same segment occupied by
> > the pre-existing callback.  The special case where all the pre-existing
> > callbacks are on a different list being invoked is handled by enqueuing
> > srcu_barrier()'s callback into the RCU_DONE_TAIL segment, relying on
> > the done-callbacks check that takes place after all callbacks are inovked.
> > 
> > Note that the readers use the same algorithm as before.  Note that there
> > is a separate srcu_idx that tells the readers what counter to increment.
> > This unfortunately cannot be combined with srcu_gp_seq because they
> > need to be incremented at different times.
> 
> So one thing I've asked before I think, would it not be possible to
> abstract PREEMPT_RCU and use the exact same code for PREEMPT_RCU and
> SRCU ?

I took a hard look at that some time ago, and it gets pretty ugly
pretty quickly.  Much of the PREEMPT_RCU code has the idea that there
is only one global PREEMPT_RCU implementation baked deeply into it.
For but one example, the handling of an arbitrarily large number of
->blkd_tasks lists at context-switch time would not be pretty, especially
if the task in question blocked while in both a PREEMPT_RCU and in an
SRCU read-side critical section.  Or, worse yet, if it blocked while in
several different SRCU read-side critical sections.

It might be easier to go the other way and implement PREEMPT_RCU in terms
of SRCU, but I don't believe that the read-side smp_mb() calls would make
people happy.  Plus there are use cases that would not be well-served
by idle no longer being an extended quiescent state.  And SRCU currently
has inconvenient restrictions about use in interrupt and NMI handlers.

It might well be that there is a global solution for all this, but
in the meantime I am instead sharing common code and doing a bit of
consolidation.

							Thanx, Paul

^ permalink raw reply	[flat|nested] 176+ messages in thread

* Re: [PATCH tip/core/rcu 02/40] rcu: Make arch select smp_mb__after_unlock_lock() strength
  2017-04-13 16:37       ` Peter Zijlstra
@ 2017-04-13 17:03         ` Paul E. McKenney
  2017-04-19 13:38           ` Michael Ellerman
  0 siblings, 1 reply; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-13 17:03 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: linux-kernel, mingo, jiangshanlai, dipankar, akpm,
	mathieu.desnoyers, josh, tglx, rostedt, dhowells, edumazet,
	fweisbec, oleg, bobby.prani, Will Deacon, Boqun Feng,
	Benjamin Herrenschmidt, Paul Mackerras, linuxppc-dev

On Thu, Apr 13, 2017 at 06:37:57PM +0200, Peter Zijlstra wrote:
> On Thu, Apr 13, 2017 at 09:26:51AM -0700, Paul E. McKenney wrote:
> 
> > ARCH_WEAK_RELEASE_ACQUIRE actually works both ways.
> > 
> > To see this, imagine some strange alternate universe in which the Power
> > hardware guys actually did decide to switch PPC to doing RCsc as you
> > suggest.  There would still be a lot of Power hardware out there that
> > still does RCpc.  Therefore, powerpc builds that needed to run on old
> > Power hardware would select ARCH_WEAK_RELEASE_ACQUIRE, while kernels
> > built to run only on the shiny new (but mythical) alternate-universe
> > Power hardware would avoid selecting this Kconfig option.
> 
> Ah, but Power software guys could do it today by replacing an LWSYNC
> with a SYNC in say arch_spin_unlock().
> 
> And yes, I know this isn't a popular suggestion, but it would do the
> trick.

Indeed, there is a fine line between motivating people to move to new
hardware on the one hand and terminally annoying existing users on
the other.  ;-)

> Its just that since there's one (PPC) we can sort of pressure them with
> the pain of being the only ones to hit all the bugs. But the moment more
> appear (and I'm afraid it'll be MIPS, with the excuse that PPC already
> does this) it will be ever so much harder to get rid of it.
> 
> Then again, maybe I should just give up and accept the Linux kernel has
> RCpc locks..

As usual, I must defer to the powerpc maintainers on this one.

							Thanx, Paul

^ permalink raw reply	[flat|nested] 176+ messages in thread

* Re: [PATCH tip/core/rcu 40/40] srcu: Parallelize callback handling
  2017-04-13 16:37     ` Paul E. McKenney
@ 2017-04-13 17:42       ` Paul E. McKenney
  0 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-13 17:42 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: linux-kernel, mingo, jiangshanlai, dipankar, akpm,
	mathieu.desnoyers, josh, tglx, rostedt, dhowells, edumazet,
	fweisbec, oleg, bobby.prani, laurent.dufour, npiggin

On Thu, Apr 13, 2017 at 09:37:10AM -0700, Paul E. McKenney wrote:
> On Thu, Apr 13, 2017 at 11:50:29AM +0200, Peter Zijlstra wrote:
> > On Wed, Apr 12, 2017 at 10:40:25AM -0700, Paul E. McKenney wrote:
> > > Peter Zijlstra proposed using SRCU to reduce mmap_sem contention [1],
> > 
> > Bugger, now you're making me feel bad for not having updated those
> > patches in ages.. I'll try and bump it on the todo list.
> 
> Apologies, I wasn't trying to make you feel bad.  But I did get an old
> version of the patch.  A much more recent one is here, which I have
> added to the commit log:
> 
> 	https://patchwork.kernel.org/patch/5108281/
> 
> For my part, I feel bad that I didn't realize much earlier that parallel
> SRCU callbacks were needed.  As it was, someone had to tell me late
> last year.

And it turns out that Laurent Dufour (CCed) forward-ported your
patch from the above patchworks URL to 4.11.  He is chasing down
some mmseq bugs on a best-effort basis.

							Thanx, Paul

> But yes, it would be really cool to have lockless VMA lookup!!!
> 
> 							Thanx, Paul

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 01/39] rcu: Maintain special bits at bottom of ->dynticks counter
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
@ 2017-04-17 23:44   ` Paul E. McKenney
  2017-04-18  0:07     ` Josh Triplett
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 02/39] rcu: Make arch select smp_mb__after_unlock_lock() strength Paul E. McKenney
                     ` (38 subsequent siblings)
  39 siblings, 1 reply; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:44 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

Currently, IPIs are used to force other CPUs to invalidate their TLBs
in response to a kernel virtual-memory mapping change.  This works, but
degrades both battery lifetime (for idle CPUs) and real-time response
(for nohz_full CPUs), and in addition results in unnecessary IPIs due to
the fact that CPUs executing in usermode are unaffected by stale kernel
mappings.  It would be better to cause a CPU executing in usermode to
wait until it is entering kernel mode to do the flush, first to avoid
interrupting usemode tasks and second to handle multiple flush requests
with a single flush in the case of a long-running user task.

This commit therefore reserves a bit at the bottom of the ->dynticks
counter, which is checked upon exit from extended quiescent states.
If it is set, it is cleared and then a new rcu_eqs_special_exit() macro is
invoked, which, if not supplied, is an empty single-pass do-while loop.
If this bottom bit is set on -entry- to an extended quiescent state,
then a WARN_ON_ONCE() triggers.

This bottom bit may be set using a new rcu_eqs_special_set() function,
which returns true if the bit was set, or false if the CPU turned
out to not be in an extended quiescent state.  Please note that this
function refuses to set the bit for a non-nohz_full CPU when that CPU
is executing in usermode because usermode execution is tracked by RCU
as a dyntick-idle extended quiescent state only for nohz_full CPUs.

Reported-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcutiny.h |  5 ++++
 kernel/rcu/tree.c       | 73 +++++++++++++++++++++++++++++++++++++++----------
 kernel/rcu/tree.h       |  1 +
 3 files changed, 65 insertions(+), 14 deletions(-)

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index b452953e21c8..6c9d941e3962 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -33,6 +33,11 @@ static inline int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
 	return 0;
 }
 
+static inline bool rcu_eqs_special_set(int cpu)
+{
+	return false;  /* Never flag non-existent other CPUs! */
+}
+
 static inline unsigned long get_state_synchronize_rcu(void)
 {
 	return 0;
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 50fee7689e71..df8f6401f2d5 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -274,9 +274,19 @@ void rcu_bh_qs(void)
 
 static DEFINE_PER_CPU(int, rcu_sched_qs_mask);
 
+/*
+ * Steal a bit from the bottom of ->dynticks for idle entry/exit
+ * control.  Initially this is for TLB flushing.
+ */
+#define RCU_DYNTICK_CTRL_MASK 0x1
+#define RCU_DYNTICK_CTRL_CTR  (RCU_DYNTICK_CTRL_MASK + 1)
+#ifndef rcu_eqs_special_exit
+#define rcu_eqs_special_exit() do { } while (0)
+#endif
+
 static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
 	.dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
-	.dynticks = ATOMIC_INIT(1),
+	.dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR),
 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
 	.dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE,
 	.dynticks_idle = ATOMIC_INIT(1),
@@ -290,15 +300,20 @@ static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
 static void rcu_dynticks_eqs_enter(void)
 {
 	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
-	int special;
+	int seq;
 
 	/*
 	 * CPUs seeing atomic_inc_return() must see prior RCU read-side
 	 * critical sections, and we also must force ordering with the
 	 * next idle sojourn.
 	 */
-	special = atomic_inc_return(&rdtp->dynticks);
-	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && special & 0x1);
+	seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
+	/* Better be in an extended quiescent state! */
+	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
+		     (seq & RCU_DYNTICK_CTRL_CTR));
+	/* Better not have special action (TLB flush) pending! */
+	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
+		     (seq & RCU_DYNTICK_CTRL_MASK));
 }
 
 /*
@@ -308,15 +323,22 @@ static void rcu_dynticks_eqs_enter(void)
 static void rcu_dynticks_eqs_exit(void)
 {
 	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
-	int special;
+	int seq;
 
 	/*
 	 * CPUs seeing atomic_inc_return() must see prior idle sojourns,
 	 * and we also must force ordering with the next RCU read-side
 	 * critical section.
 	 */
-	special = atomic_inc_return(&rdtp->dynticks);
-	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(special & 0x1));
+	seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
+	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
+		     !(seq & RCU_DYNTICK_CTRL_CTR));
+	if (seq & RCU_DYNTICK_CTRL_MASK) {
+		atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdtp->dynticks);
+		smp_mb__after_atomic(); /* _exit after clearing mask. */
+		/* Prefer duplicate flushes to losing a flush. */
+		rcu_eqs_special_exit();
+	}
 }
 
 /*
@@ -333,9 +355,9 @@ static void rcu_dynticks_eqs_online(void)
 {
 	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
 
-	if (atomic_read(&rdtp->dynticks) & 0x1)
+	if (atomic_read(&rdtp->dynticks) & RCU_DYNTICK_CTRL_CTR)
 		return;
-	atomic_add(0x1, &rdtp->dynticks);
+	atomic_add(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
 }
 
 /*
@@ -347,7 +369,7 @@ bool rcu_dynticks_curr_cpu_in_eqs(void)
 {
 	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
 
-	return !(atomic_read(&rdtp->dynticks) & 0x1);
+	return !(atomic_read(&rdtp->dynticks) & RCU_DYNTICK_CTRL_CTR);
 }
 
 /*
@@ -358,7 +380,7 @@ int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
 {
 	int snap = atomic_add_return(0, &rdtp->dynticks);
 
-	return snap;
+	return snap & ~RCU_DYNTICK_CTRL_MASK;
 }
 
 /*
@@ -367,7 +389,7 @@ int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
  */
 static bool rcu_dynticks_in_eqs(int snap)
 {
-	return !(snap & 0x1);
+	return !(snap & RCU_DYNTICK_CTRL_CTR);
 }
 
 /*
@@ -387,10 +409,33 @@ static bool rcu_dynticks_in_eqs_since(struct rcu_dynticks *rdtp, int snap)
 static void rcu_dynticks_momentary_idle(void)
 {
 	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
-	int special = atomic_add_return(2, &rdtp->dynticks);
+	int special = atomic_add_return(2 * RCU_DYNTICK_CTRL_CTR,
+					&rdtp->dynticks);
 
 	/* It is illegal to call this from idle state. */
-	WARN_ON_ONCE(!(special & 0x1));
+	WARN_ON_ONCE(!(special & RCU_DYNTICK_CTRL_CTR));
+}
+
+/*
+ * Set the special (bottom) bit of the specified CPU so that it
+ * will take special action (such as flushing its TLB) on the
+ * next exit from an extended quiescent state.  Returns true if
+ * the bit was successfully set, or false if the CPU was not in
+ * an extended quiescent state.
+ */
+bool rcu_eqs_special_set(int cpu)
+{
+	int old;
+	int new;
+	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
+
+	do {
+		old = atomic_read(&rdtp->dynticks);
+		if (old & RCU_DYNTICK_CTRL_CTR)
+			return false;
+		new = old | RCU_DYNTICK_CTRL_MASK;
+	} while (atomic_cmpxchg(&rdtp->dynticks, old, new) != old);
+	return true;
 }
 
 DEFINE_PER_CPU_SHARED_ALIGNED(unsigned long, rcu_qs_ctr);
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index ec62a05bfdb3..7468b4de7e0c 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -596,6 +596,7 @@ extern struct rcu_state rcu_preempt_state;
 #endif /* #ifdef CONFIG_PREEMPT_RCU */
 
 int rcu_dynticks_snap(struct rcu_dynticks *rdtp);
+bool rcu_eqs_special_set(int cpu);
 
 #ifdef CONFIG_RCU_BOOST
 DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 02/39] rcu: Make arch select smp_mb__after_unlock_lock() strength
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 01/39] rcu: Maintain special bits at bottom of ->dynticks counter Paul E. McKenney
@ 2017-04-17 23:44   ` Paul E. McKenney
  2017-04-18  0:19     ` Josh Triplett
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 03/39] srcu: Consolidate batch checking into rcu_all_batches_empty() Paul E. McKenney
                     ` (37 subsequent siblings)
  39 siblings, 1 reply; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:44 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney, Will Deacon, Boqun Feng,
	Benjamin Herrenschmidt, Paul Mackerras, linuxppc-dev

The definition of smp_mb__after_unlock_lock() is currently smp_mb()
for CONFIG_PPC and a no-op otherwise.  It would be better to instead
provide an architecture-selectable Kconfig option, and select the
strength of smp_mb__after_unlock_lock() based on that option.  This
commit therefore creates ARCH_WEAK_RELEASE_ACQUIRE, has PPC select it,
and bases the definition of smp_mb__after_unlock_lock() on this new
ARCH_WEAK_RELEASE_ACQUIRE Kconfig option.

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Boqun Feng <boqun.feng@linux.vnet.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: <linuxppc-dev@lists.ozlabs.org>
---
 arch/Kconfig             | 3 +++
 arch/powerpc/Kconfig     | 1 +
 include/linux/rcupdate.h | 6 +++---
 3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index cd211a14a88f..adefaf344239 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -320,6 +320,9 @@ config HAVE_CMPXCHG_LOCAL
 config HAVE_CMPXCHG_DOUBLE
 	bool
 
+config ARCH_WEAK_RELEASE_ACQUIRE
+	bool
+
 config ARCH_WANT_IPC_PARSE_VERSION
 	bool
 
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 97a8bc8a095c..7a5c9b764cd2 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -99,6 +99,7 @@ config PPC
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF		if PPC64
 	select ARCH_WANT_IPC_PARSE_VERSION
+	select ARCH_WEAK_RELEASE_ACQUIRE
 	select BINFMT_ELF
 	select BUILDTIME_EXTABLE_SORT
 	select CLONE_BACKWARDS
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index de88b33c0974..e6146d0074f8 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -1127,11 +1127,11 @@ do { \
  * if the UNLOCK and LOCK are executed by the same CPU or if the
  * UNLOCK and LOCK operate on the same lock variable.
  */
-#ifdef CONFIG_PPC
+#ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE
 #define smp_mb__after_unlock_lock()	smp_mb()  /* Full ordering for lock. */
-#else /* #ifdef CONFIG_PPC */
+#else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
 #define smp_mb__after_unlock_lock()	do { } while (0)
-#endif /* #else #ifdef CONFIG_PPC */
+#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
 
 
 #endif /* __LINUX_RCUPDATE_H */
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 03/39] srcu: Consolidate batch checking into rcu_all_batches_empty()
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 01/39] rcu: Maintain special bits at bottom of ->dynticks counter Paul E. McKenney
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 02/39] rcu: Make arch select smp_mb__after_unlock_lock() strength Paul E. McKenney
@ 2017-04-17 23:44   ` Paul E. McKenney
  2017-04-18  0:30     ` Josh Triplett
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 04/39] srcu: Check for tardy grace-period activity in cleanup_srcu_struct() Paul E. McKenney
                     ` (36 subsequent siblings)
  39 siblings, 1 reply; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:44 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The srcu_reschedule() function invokes rcu_batch_empty() on each of
the four rcu_batch structures in the srcu_struct in question twice.
Given that this check will also be needed in cleanup_srcu_struct(), this
commit consolidates these four checks into a new rcu_all_batches_empty()
function.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/srcu.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index ef3bcfb15b39..ba41a5d04b49 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -65,6 +65,17 @@ static inline bool rcu_batch_empty(struct rcu_batch *b)
 }
 
 /*
+ * Are all batches empty for the specified srcu_struct?
+ */
+static inline bool rcu_all_batches_empty(struct srcu_struct *sp)
+{
+	return rcu_batch_empty(&sp->batch_done) &&
+	       rcu_batch_empty(&sp->batch_check1) &&
+	       rcu_batch_empty(&sp->batch_check0) &&
+	       rcu_batch_empty(&sp->batch_queue);
+}
+
+/*
  * Remove the callback at the head of the specified rcu_batch structure
  * and return a pointer to it, or return NULL if the structure is empty.
  */
@@ -619,15 +630,9 @@ static void srcu_reschedule(struct srcu_struct *sp)
 {
 	bool pending = true;
 
-	if (rcu_batch_empty(&sp->batch_done) &&
-	    rcu_batch_empty(&sp->batch_check1) &&
-	    rcu_batch_empty(&sp->batch_check0) &&
-	    rcu_batch_empty(&sp->batch_queue)) {
+	if (rcu_all_batches_empty(sp)) {
 		spin_lock_irq(&sp->queue_lock);
-		if (rcu_batch_empty(&sp->batch_done) &&
-		    rcu_batch_empty(&sp->batch_check1) &&
-		    rcu_batch_empty(&sp->batch_check0) &&
-		    rcu_batch_empty(&sp->batch_queue)) {
+		if (rcu_all_batches_empty(sp)) {
 			sp->running = false;
 			pending = false;
 		}
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 04/39] srcu: Check for tardy grace-period activity in cleanup_srcu_struct()
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (2 preceding siblings ...)
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 03/39] srcu: Consolidate batch checking into rcu_all_batches_empty() Paul E. McKenney
@ 2017-04-17 23:44   ` Paul E. McKenney
  2017-04-18  0:33     ` Josh Triplett
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 05/39] rcu: Semicolon inside RCU_TRACE() for rcu.h Paul E. McKenney
                     ` (35 subsequent siblings)
  39 siblings, 1 reply; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:44 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

Users of SRCU are obliged to complete all grace-period activity before
invoking cleanup_srcu_struct().  This means that all calls to either
synchronize_srcu() or synchronize_srcu_expedited() must have returned,
and all calls to call_srcu() must have returned, and the last call to
call_srcu() must have been followed by a call to srcu_barrier().
Furthermore, the caller must have done something to prevent any
further calls to synchronize_srcu(), synchronize_srcu_expedited(),
and call_srcu().

Therefore, if there has ever been an invocation of call_srcu() on
the srcu_struct in question, the sequence of events must be as
follows:

1.  Prevent any further calls to call_srcu().
2.  Wait for any pre-existing call_srcu() invocations to return.
3.  Invoke srcu_barrier().
4.  It is now safe to invoke cleanup_srcu_struct().

On the other hand, if there has ever been a call to synchronize_srcu()
or synchronize_srcu_expedited(), the sequence of events must be as
follows:

1.  Prevent any further calls to synchronize_srcu() or
    synchronize_srcu_expedited().
2.  Wait for any pre-existing synchronize_srcu() or
    synchronize_srcu_expedited() invocations to return.
3.  It is now safe to invoke cleanup_srcu_struct().

If there have been calls to all both types of functions (call_srcu()
and either of synchronize_srcu() and synchronize_srcu_expedited()), then
the caller must do the first three steps of the call_srcu() procedure
above and the first two steps of the synchronize_s*() procedure above,
and only then invoke cleanup_srcu_struct().

Reported-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/srcu.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index ba41a5d04b49..6beeba7b0b67 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -261,6 +261,11 @@ void cleanup_srcu_struct(struct srcu_struct *sp)
 {
 	if (WARN_ON(srcu_readers_active(sp)))
 		return; /* Leakage unless caller handles error. */
+	if (WARN_ON(!rcu_all_batches_empty(sp)))
+		return; /* Leakage unless caller handles error. */
+	flush_delayed_work(&sp->work);
+	if (WARN_ON(sp->running))
+		return; /* Caller forgot to stop doing call_srcu()? */
 	free_percpu(sp->per_cpu_ref);
 	sp->per_cpu_ref = NULL;
 }
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12
  2017-04-12 17:40 [PATCH tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                   ` (39 preceding siblings ...)
  2017-04-12 17:40 ` [PATCH tip/core/rcu 40/40] srcu: Parallelize callback handling Paul E. McKenney
@ 2017-04-17 23:44 ` Paul E. McKenney
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 01/39] rcu: Maintain special bits at bottom of ->dynticks counter Paul E. McKenney
                     ` (39 more replies)
  40 siblings, 40 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:44 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani

Hello!

This v2 series moves SRCU from its traditional single per-srcu_struct
callback queue to per-srcu_struct/per-CPU callback queues.  This involves
abstracting functionality from Tree RCU, which results in a large
conflict footprint, which in turn results in some otherwise unrelated
patches coming along for the ride.

1.	Maintain special bits at bottom of ->dynticks counter.
	This is for some upcoming MM work.  My intent was to hold
	it until that work was ready, but merge conflicts dictated
	otherwise.  If the MM work does not appear soonish, I will
	manually revert this patch.

2.	Make arch select smp_mb__after_unlock_lock() strength, which
	gets rid of an arch-specific #ifdef.

3.	Consolidate SRCU batch checking into rcu_all_batches_empty().

4.	Check for tardy grace-period activity in cleanup_srcu_struct().

5-7.	Semicolon inside RCU_TRACE() for various parts of RCU.

8.	Pull rcu_sched_qs_mask into rcu_dynticks structure in order to
	eliminate an isolated per-CPU variable.

9.	Pull rcu_qs_ctr into rcu_dynticks structure.

10.	Eliminate flavor scan in rcu_momentary_dyntick_idle() to
	reduce semi-common-case context-switch overhead.

11.	Place guard on rcu_all_qs() and rcu_note_context_switch()
	actions to reduce common-case scheduler-fastpath overhead.

12.	Default RCU_FANOUT_LEAF to 16 unless explicitly changed.

13.	Abstract multi-tail callback list handling for SRCU.

14.	Allow SRCU to access rcu_scheduler_active.

15.	Allow early boot use of synchronize_srcu(), though not yet
	mid-boot use.

16.	Add single-element dequeue functions to rcu_segcblist for
	debug use.

17.	Move rcu_seq_start() and friends to rcu.h for SRCU's benefit.

18.	Expedited wakeups need to be fully ordered.

19.	Fix warning in rcu_seq_end().

20.	Push srcu_advance_batches() fastpath into common case as a
	step towards callback parallelization.

21.	Move to state-based grace-period sequencing, also as a step
	towards callback parallelization.

22.	Add grace-period sequence numbers to SRCU.

23.	Use rcu_segcblist to track SRCU callbacks.

24.	Move combining-tree definitions for SRCU's benefit.

25.	Move rcu_init_levelspread() to rcu_tree_node.h for SRCU's benefit.

26.	Remove redundant levelcnt[] array from rcu_init_one().

27.	Move rcu_node traversal macros to rcu.h for SRCU's benefit.

28.	Make num_rcu_lvl[] array be external for SRCU's benefit.

29.	Fix bogus try_check_zero() comment.

30.	Improve rcu_seq grace-period-counter abstraction for SRCU's
	benefit.

31.	Allow a second bit in rcu_seq for SRCU state.

32.	Merge ->srcu_state into ->srcu_gp_seq to allow atomic updates.

33.	Provide crude control of expedited SRCU grace periods.

34.	Use static initialization for "srcu" in mm/mmu_notifier.c.

35.	Create a tiny SRCU for bloatwatch/tinification.

36.	Print Tiny SRCU reader statistics in rcutorture.

37.	Introduce CLASSIC_SRCU Kconfig option for those who do not
	wish to help debug Tree SRCU.

38.	Parallelize SRCU callback handling.

39.	Make non-preemptive schedule be Tasks RCU quiescent state.

Updates since v1:

o	Incorporate feedback from Peter Zijlstra.

o	Dropped v1 patches 8-10 ("Make various parts of RCU do deferred
	NOCB wakeups in order to prevent callback blockages, and thus
	hangs").  These patches turned out to be papering over a no-CBs
	CPU design flaw.  There will be patches in v4.13 to fix the design
	flaw directly.

o	Added v2 patch #34 ("Use static initialization for "srcu" in
	mm/mmu_notifier.c"), moving it from its v1 location in the
	fixes series.

o	Added v2 patch #39 ("Make non-preemptive schedule be Tasks RCU
	quiescent state") for the benefit of upcoming ftrace work at
	Steve Rostedt's request.

							Thanx, Paul

------------------------------------------------------------------------

 /kernel/rcu/rcu_segcblist.h                                     |  670 -----
 b/Documentation/RCU/Design/Data-Structures/Data-Structures.html |   36 
 b/arch/Kconfig                                                  |    3 
 b/arch/powerpc/Kconfig                                          |    1 
 b/include/linux/rcu_node_tree.h                                 |  105 
 b/include/linux/rcu_segcblist.h                                 |  720 +++++
 b/include/linux/rcupdate.h                                      |   17 
 b/include/linux/rcutiny.h                                       |   24 
 b/include/linux/rcutree.h                                       |    5 
 b/include/linux/srcu.h                                          |  112 
 b/include/linux/srcuclassic.h                                   |  101 
 b/include/linux/srcutiny.h                                      |   81 
 b/include/linux/srcutree.h                                      |  171 +
 b/init/Kconfig                                                  |   33 
 b/kernel/rcu/Makefile                                           |    6 
 b/kernel/rcu/rcu.h                                              |  165 +
 b/kernel/rcu/rcu_segcblist.h                                    |  670 +++++
 b/kernel/rcu/rcutorture.c                                       |   39 
 b/kernel/rcu/srcu.c                                             |  846 +++---
 b/kernel/rcu/srcutiny.c                                         |  215 +
 b/kernel/rcu/srcutree.c                                         | 1252 ++++++++--
 b/kernel/rcu/tiny.c                                             |   20 
 b/kernel/rcu/tiny_plugin.h                                      |   13 
 b/kernel/rcu/tree.c                                             |  657 ++---
 b/kernel/rcu/tree.h                                             |  174 -
 b/kernel/rcu/tree_exp.h                                         |   25 
 b/kernel/rcu/tree_plugin.h                                      |   62 
 b/kernel/rcu/tree_trace.c                                       |   26 
 b/kernel/rcu/update.c                                           |   53 
 b/kernel/sched/core.c                                           |    2 
 b/mm/mmu_notifier.c                                             |   14 
 31 files changed, 4287 insertions(+), 2031 deletions(-)

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 05/39] rcu: Semicolon inside RCU_TRACE() for rcu.h
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (3 preceding siblings ...)
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 04/39] srcu: Check for tardy grace-period activity in cleanup_srcu_struct() Paul E. McKenney
@ 2017-04-17 23:44   ` Paul E. McKenney
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 06/39] rcu: Semicolon inside RCU_TRACE() for Tiny RCU Paul E. McKenney
                     ` (34 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:44 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The current use of "RCU_TRACE(statement);" can cause odd bugs, especially
where "statement" is a local-variable declaration, as it can leave a
misplaced ";" in the source code.  This commit therefore converts these
to "RCU_TRACE(statement;)", which avoids the misplaced ";".

Reported-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcu.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 0d6ff3e471be..8700a81daf56 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -109,12 +109,12 @@ static inline bool __rcu_reclaim(const char *rn, struct rcu_head *head)
 
 	rcu_lock_acquire(&rcu_callback_map);
 	if (__is_kfree_rcu_offset(offset)) {
-		RCU_TRACE(trace_rcu_invoke_kfree_callback(rn, head, offset));
+		RCU_TRACE(trace_rcu_invoke_kfree_callback(rn, head, offset);)
 		kfree((void *)head - offset);
 		rcu_lock_release(&rcu_callback_map);
 		return true;
 	} else {
-		RCU_TRACE(trace_rcu_invoke_callback(rn, head));
+		RCU_TRACE(trace_rcu_invoke_callback(rn, head);)
 		head->func(head);
 		rcu_lock_release(&rcu_callback_map);
 		return false;
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 06/39] rcu: Semicolon inside RCU_TRACE() for Tiny RCU
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (4 preceding siblings ...)
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 05/39] rcu: Semicolon inside RCU_TRACE() for rcu.h Paul E. McKenney
@ 2017-04-17 23:44   ` Paul E. McKenney
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 07/39] rcu: Semicolon inside RCU_TRACE() for tree.c Paul E. McKenney
                     ` (33 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:44 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The current use of "RCU_TRACE(statement);" can cause odd bugs, especially
where "statement" is a local-variable declaration, as it can leave a
misplaced ";" in the source code.  This commit therefore converts these
to "RCU_TRACE(statement;)", which avoids the misplaced ";".

Reported-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tiny.c        | 20 ++++++++++----------
 kernel/rcu/tiny_plugin.h |  4 ++--
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index 6ad330dbbae2..e5385731e391 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -79,7 +79,7 @@ EXPORT_SYMBOL(__rcu_is_watching);
  */
 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
 {
-	RCU_TRACE(reset_cpu_stall_ticks(rcp));
+	RCU_TRACE(reset_cpu_stall_ticks(rcp);)
 	if (rcp->donetail != rcp->curtail) {
 		rcp->donetail = rcp->curtail;
 		return 1;
@@ -125,7 +125,7 @@ void rcu_bh_qs(void)
  */
 void rcu_check_callbacks(int user)
 {
-	RCU_TRACE(check_cpu_stalls());
+	RCU_TRACE(check_cpu_stalls();)
 	if (user)
 		rcu_sched_qs();
 	else if (!in_softirq())
@@ -143,7 +143,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 	const char *rn = NULL;
 	struct rcu_head *next, *list;
 	unsigned long flags;
-	RCU_TRACE(int cb_count = 0);
+	RCU_TRACE(int cb_count = 0;)
 
 	/* Move the ready-to-invoke callbacks to a local list. */
 	local_irq_save(flags);
@@ -152,7 +152,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 		local_irq_restore(flags);
 		return;
 	}
-	RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
+	RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1);)
 	list = rcp->rcucblist;
 	rcp->rcucblist = *rcp->donetail;
 	*rcp->donetail = NULL;
@@ -162,7 +162,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 	local_irq_restore(flags);
 
 	/* Invoke the callbacks on the local list. */
-	RCU_TRACE(rn = rcp->name);
+	RCU_TRACE(rn = rcp->name;)
 	while (list) {
 		next = list->next;
 		prefetch(next);
@@ -171,9 +171,9 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 		__rcu_reclaim(rn, list);
 		local_bh_enable();
 		list = next;
-		RCU_TRACE(cb_count++);
+		RCU_TRACE(cb_count++;)
 	}
-	RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
+	RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count);)
 	RCU_TRACE(trace_rcu_batch_end(rcp->name,
 				      cb_count, 0, need_resched(),
 				      is_idle_task(current),
@@ -221,7 +221,7 @@ static void __call_rcu(struct rcu_head *head,
 	local_irq_save(flags);
 	*rcp->curtail = head;
 	rcp->curtail = &head->next;
-	RCU_TRACE(rcp->qlen++);
+	RCU_TRACE(rcp->qlen++;)
 	local_irq_restore(flags);
 
 	if (unlikely(is_idle_task(current))) {
@@ -254,8 +254,8 @@ EXPORT_SYMBOL_GPL(call_rcu_bh);
 void __init rcu_init(void)
 {
 	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
-	RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk));
-	RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk));
+	RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk);)
+	RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk);)
 
 	rcu_early_boot_tests();
 }
diff --git a/kernel/rcu/tiny_plugin.h b/kernel/rcu/tiny_plugin.h
index c64b827ecbca..df3a60e19f07 100644
--- a/kernel/rcu/tiny_plugin.h
+++ b/kernel/rcu/tiny_plugin.h
@@ -162,8 +162,8 @@ static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
 
 static void check_cpu_stalls(void)
 {
-	RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
-	RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
+	RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk);)
+	RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk);)
 }
 
 #endif /* #ifdef CONFIG_RCU_TRACE */
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 07/39] rcu: Semicolon inside RCU_TRACE() for tree.c
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (5 preceding siblings ...)
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 06/39] rcu: Semicolon inside RCU_TRACE() for Tiny RCU Paul E. McKenney
@ 2017-04-17 23:44   ` Paul E. McKenney
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 08/39] rcu: Pull rcu_sched_qs_mask into rcu_dynticks structure Paul E. McKenney
                     ` (32 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:44 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The current use of "RCU_TRACE(statement);" can cause odd bugs, especially
where "statement" is a local-variable declaration, as it can leave a
misplaced ";" in the source code.  This commit therefore converts these
to "RCU_TRACE(statement;)", which avoids the misplaced ";".

Reported-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index df8f6401f2d5..e8843bf0f5e1 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2793,14 +2793,14 @@ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
  */
 static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
 {
-	RCU_TRACE(unsigned long mask);
-	RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda));
-	RCU_TRACE(struct rcu_node *rnp = rdp->mynode);
+	RCU_TRACE(unsigned long mask;)
+	RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda);)
+	RCU_TRACE(struct rcu_node *rnp = rdp->mynode;)
 
 	if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
 		return;
 
-	RCU_TRACE(mask = rdp->grpmask);
+	RCU_TRACE(mask = rdp->grpmask;)
 	trace_rcu_grace_period(rsp->name,
 			       rnp->gpnum + 1 - !!(rnp->qsmask & mask),
 			       TPS("cpuofl"));
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 08/39] rcu: Pull rcu_sched_qs_mask into rcu_dynticks structure
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (6 preceding siblings ...)
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 07/39] rcu: Semicolon inside RCU_TRACE() for tree.c Paul E. McKenney
@ 2017-04-17 23:44   ` Paul E. McKenney
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 09/39] rcu: Pull rcu_qs_ctr " Paul E. McKenney
                     ` (31 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:44 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The rcu_sched_qs_mask variable is yet another isolated per-CPU variable,
so this commit pulls it into the pre-existing rcu_dynticks per-CPU
structure.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 .../RCU/Design/Data-Structures/Data-Structures.html          |  9 ++++++++-
 kernel/rcu/tree.c                                            | 12 +++++-------
 kernel/rcu/tree.h                                            |  1 +
 3 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.html b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
index d583c653a703..bf7f266e8888 100644
--- a/Documentation/RCU/Design/Data-Structures/Data-Structures.html
+++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
@@ -1104,6 +1104,7 @@ Its fields are as follows:
   1   int dynticks_nesting;
   2   int dynticks_nmi_nesting;
   3   atomic_t dynticks;
+  4   int rcu_sched_qs_mask;
 </pre>
 
 <p>The <tt>-&gt;dynticks_nesting</tt> field counts the
@@ -1117,11 +1118,17 @@ NMIs are counted by the <tt>-&gt;dynticks_nmi_nesting</tt>
 field, except that NMIs that interrupt non-dyntick-idle execution
 are not counted.
 
-</p><p>Finally, the <tt>-&gt;dynticks</tt> field counts the corresponding
+</p><p>The <tt>-&gt;dynticks</tt> field counts the corresponding
 CPU's transitions to and from dyntick-idle mode, so that this counter
 has an even value when the CPU is in dyntick-idle mode and an odd
 value otherwise.
 
+</p><p>Finally, the  <tt>-&gt;rcu_sched_qs_mask</tt> field is used
+to record the fact that the RCU core code would really like to
+see a quiescent state from the corresponding CPU.
+This flag is checked by RCU's context-switch and <tt>cond_resched()</tt>
+code, which provide a momentary idle sojourn in response.
+
 <table>
 <tr><th>&nbsp;</th></tr>
 <tr><th align="left">Quick Quiz:</th></tr>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index e8843bf0f5e1..0e8d91f36bb6 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -272,8 +272,6 @@ void rcu_bh_qs(void)
 	}
 }
 
-static DEFINE_PER_CPU(int, rcu_sched_qs_mask);
-
 /*
  * Steal a bit from the bottom of ->dynticks for idle entry/exit
  * control.  Initially this is for TLB flushing.
@@ -464,8 +462,8 @@ static void rcu_momentary_dyntick_idle(void)
 	 * Yes, we can lose flag-setting operations.  This is OK, because
 	 * the flag will be set again after some delay.
 	 */
-	resched_mask = raw_cpu_read(rcu_sched_qs_mask);
-	raw_cpu_write(rcu_sched_qs_mask, 0);
+	resched_mask = raw_cpu_read(rcu_dynticks.rcu_sched_qs_mask);
+	raw_cpu_write(rcu_dynticks.rcu_sched_qs_mask, 0);
 
 	/* Find the flavor that needs a quiescent state. */
 	for_each_rcu_flavor(rsp) {
@@ -499,7 +497,7 @@ void rcu_note_context_switch(void)
 	trace_rcu_utilization(TPS("Start context switch"));
 	rcu_sched_qs();
 	rcu_preempt_note_context_switch();
-	if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
+	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_sched_qs_mask)))
 		rcu_momentary_dyntick_idle();
 	trace_rcu_utilization(TPS("End context switch"));
 	barrier(); /* Avoid RCU read-side critical sections leaking up. */
@@ -524,7 +522,7 @@ void rcu_all_qs(void)
 	unsigned long flags;
 
 	barrier(); /* Avoid RCU read-side critical sections leaking down. */
-	if (unlikely(raw_cpu_read(rcu_sched_qs_mask))) {
+	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_sched_qs_mask))) {
 		local_irq_save(flags);
 		rcu_momentary_dyntick_idle();
 		local_irq_restore(flags);
@@ -1351,7 +1349,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 	 * is set too high, we override with half of the RCU CPU stall
 	 * warning delay.
 	 */
-	rcrmp = &per_cpu(rcu_sched_qs_mask, rdp->cpu);
+	rcrmp = &per_cpu(rcu_dynticks.rcu_sched_qs_mask, rdp->cpu);
 	if (time_after(jiffies, rdp->rsp->gp_start + jtsq) ||
 	    time_after(jiffies, rdp->rsp->jiffies_resched)) {
 		if (!(READ_ONCE(*rcrmp) & rdp->rsp->flavor_mask)) {
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 7468b4de7e0c..e298281984dc 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -113,6 +113,7 @@ struct rcu_dynticks {
 				    /* Process level is worth LLONG_MAX/2. */
 	int dynticks_nmi_nesting;   /* Track NMI nesting level. */
 	atomic_t dynticks;	    /* Even value for idle, else odd. */
+	int rcu_sched_qs_mask;      /* GP old, need quiescent state. */
 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
 	long long dynticks_idle_nesting;
 				    /* irq/process nesting level from idle. */
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 09/39] rcu: Pull rcu_qs_ctr into rcu_dynticks structure
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (7 preceding siblings ...)
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 08/39] rcu: Pull rcu_sched_qs_mask into rcu_dynticks structure Paul E. McKenney
@ 2017-04-17 23:44   ` Paul E. McKenney
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 10/39] rcu: Eliminate flavor scan in rcu_momentary_dyntick_idle() Paul E. McKenney
                     ` (30 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:44 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The rcu_qs_ctr variable is yet another isolated per-CPU variable,
so this commit pulls it into the pre-existing rcu_dynticks per-CPU
structure.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 .../RCU/Design/Data-Structures/Data-Structures.html       | 12 ++++++++++--
 kernel/rcu/tree.c                                         | 15 ++++++---------
 kernel/rcu/tree.h                                         |  3 ++-
 kernel/rcu/tree_trace.c                                   |  4 +---
 4 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.html b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
index bf7f266e8888..3d0311657533 100644
--- a/Documentation/RCU/Design/Data-Structures/Data-Structures.html
+++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
@@ -1105,6 +1105,7 @@ Its fields are as follows:
   2   int dynticks_nmi_nesting;
   3   atomic_t dynticks;
   4   int rcu_sched_qs_mask;
+  5   unsigned long rcu_qs_ctr;
 </pre>
 
 <p>The <tt>-&gt;dynticks_nesting</tt> field counts the
@@ -1123,12 +1124,19 @@ CPU's transitions to and from dyntick-idle mode, so that this counter
 has an even value when the CPU is in dyntick-idle mode and an odd
 value otherwise.
 
-</p><p>Finally, the  <tt>-&gt;rcu_sched_qs_mask</tt> field is used
+</p><p>The <tt>-&gt;rcu_sched_qs_mask</tt> field is used
 to record the fact that the RCU core code would really like to
-see a quiescent state from the corresponding CPU.
+see a quiescent state from the corresponding CPU, so much so that
+it is willing to call for heavy-weight dyntick-counter operations.
 This flag is checked by RCU's context-switch and <tt>cond_resched()</tt>
 code, which provide a momentary idle sojourn in response.
 
+</p><p>Finally the <tt>-&gt;rcu_qs_ctr</tt> field is used to record
+quiescent states from <tt>cond_resched()</tt>.
+Because <tt>cond_resched()</tt> can execute quite frequently, this
+must be quite lightweight, as in a non-atomic increment of this
+per-CPU field.
+
 <table>
 <tr><th>&nbsp;</th></tr>
 <tr><th align="left">Quick Quiz:</th></tr>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 0e8d91f36bb6..fbee1d729c4b 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -436,9 +436,6 @@ bool rcu_eqs_special_set(int cpu)
 	return true;
 }
 
-DEFINE_PER_CPU_SHARED_ALIGNED(unsigned long, rcu_qs_ctr);
-EXPORT_PER_CPU_SYMBOL_GPL(rcu_qs_ctr);
-
 /*
  * Let the RCU core know that this CPU has gone through the scheduler,
  * which is a quiescent state.  This is called when the need for a
@@ -542,7 +539,7 @@ void rcu_all_qs(void)
 		rcu_sched_qs();
 		preempt_enable();
 	}
-	this_cpu_inc(rcu_qs_ctr);
+	this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
 	barrier(); /* Avoid RCU read-side critical sections leaking up. */
 }
 EXPORT_SYMBOL_GPL(rcu_all_qs);
@@ -1315,7 +1312,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 	 */
 	rnp = rdp->mynode;
 	if (time_after(jiffies, rdp->rsp->gp_start + jtsq) &&
-	    READ_ONCE(rdp->rcu_qs_ctr_snap) != per_cpu(rcu_qs_ctr, rdp->cpu) &&
+	    READ_ONCE(rdp->rcu_qs_ctr_snap) != per_cpu(rcu_dynticks.rcu_qs_ctr, rdp->cpu) &&
 	    READ_ONCE(rdp->gpnum) == rnp->gpnum && !rdp->gpwrap) {
 		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("rqc"));
 		return 1;
@@ -2024,7 +2021,7 @@ static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
 		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
 		need_gp = !!(rnp->qsmask & rdp->grpmask);
 		rdp->cpu_no_qs.b.norm = need_gp;
-		rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
+		rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr);
 		rdp->core_needs_qs = need_gp;
 		zero_cpu_stall_ticks(rdp);
 		WRITE_ONCE(rdp->gpwrap, false);
@@ -2622,7 +2619,7 @@ rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
 		 * within the current grace period.
 		 */
 		rdp->cpu_no_qs.b.norm = true;	/* need qs for new gp. */
-		rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
+		rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr);
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 		return;
 	}
@@ -3620,7 +3617,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
 	/* Is the RCU core waiting for a quiescent state from this CPU? */
 	if (rcu_scheduler_fully_active &&
 	    rdp->core_needs_qs && rdp->cpu_no_qs.b.norm &&
-	    rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) {
+	    rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_dynticks.rcu_qs_ctr)) {
 		rdp->n_rp_core_needs_qs++;
 	} else if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm) {
 		rdp->n_rp_report_qs++;
@@ -3933,7 +3930,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
 	rdp->gpnum = rnp->completed; /* Make CPU later note any new GP. */
 	rdp->completed = rnp->completed;
 	rdp->cpu_no_qs.b.norm = true;
-	rdp->rcu_qs_ctr_snap = per_cpu(rcu_qs_ctr, cpu);
+	rdp->rcu_qs_ctr_snap = per_cpu(rcu_dynticks.rcu_qs_ctr, cpu);
 	rdp->core_needs_qs = false;
 	trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index e298281984dc..76e4467bc765 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -113,7 +113,8 @@ struct rcu_dynticks {
 				    /* Process level is worth LLONG_MAX/2. */
 	int dynticks_nmi_nesting;   /* Track NMI nesting level. */
 	atomic_t dynticks;	    /* Even value for idle, else odd. */
-	int rcu_sched_qs_mask;      /* GP old, need quiescent state. */
+	int rcu_sched_qs_mask;      /* GP old, need heavy quiescent state. */
+	unsigned long rcu_qs_ctr;   /* Light universal quiescent state ctr. */
 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
 	long long dynticks_idle_nesting;
 				    /* irq/process nesting level from idle. */
diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c
index 8751a748499a..65b43be38e68 100644
--- a/kernel/rcu/tree_trace.c
+++ b/kernel/rcu/tree_trace.c
@@ -45,8 +45,6 @@
 #define RCU_TREE_NONCORE
 #include "tree.h"
 
-DECLARE_PER_CPU_SHARED_ALIGNED(unsigned long, rcu_qs_ctr);
-
 static int r_open(struct inode *inode, struct file *file,
 					const struct seq_operations *op)
 {
@@ -121,7 +119,7 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
 		   cpu_is_offline(rdp->cpu) ? '!' : ' ',
 		   ulong2long(rdp->completed), ulong2long(rdp->gpnum),
 		   rdp->cpu_no_qs.b.norm,
-		   rdp->rcu_qs_ctr_snap == per_cpu(rcu_qs_ctr, rdp->cpu),
+		   rdp->rcu_qs_ctr_snap == per_cpu(rdp->dynticks->rcu_qs_ctr, rdp->cpu),
 		   rdp->core_needs_qs);
 	seq_printf(m, " dt=%d/%llx/%d df=%lu",
 		   rcu_dynticks_snap(rdp->dynticks),
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 10/39] rcu: Eliminate flavor scan in rcu_momentary_dyntick_idle()
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (8 preceding siblings ...)
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 09/39] rcu: Pull rcu_qs_ctr " Paul E. McKenney
@ 2017-04-17 23:44   ` Paul E. McKenney
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 11/39] rcu: Place guard on rcu_all_qs() and rcu_note_context_switch() actions Paul E. McKenney
                     ` (29 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:44 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The rcu_momentary_dyntick_idle() function scans the RCU flavors, checking
that one of them still needs a quiescent state before doing an expensive
atomic operation on the ->dynticks counter.  However, this check reduces
overhead only after a rare race condition, and increases complexity.  This
commit therefore removes the scan and the mechanism enabling the scan.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 .../Design/Data-Structures/Data-Structures.html    |  4 +-
 kernel/rcu/tree.c                                  | 62 +++++-----------------
 kernel/rcu/tree.h                                  |  3 +-
 3 files changed, 15 insertions(+), 54 deletions(-)

diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.html b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
index 3d0311657533..e4bf20a68fa3 100644
--- a/Documentation/RCU/Design/Data-Structures/Data-Structures.html
+++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
@@ -1104,7 +1104,7 @@ Its fields are as follows:
   1   int dynticks_nesting;
   2   int dynticks_nmi_nesting;
   3   atomic_t dynticks;
-  4   int rcu_sched_qs_mask;
+  4   bool rcu_need_heavy_qs;
   5   unsigned long rcu_qs_ctr;
 </pre>
 
@@ -1124,7 +1124,7 @@ CPU's transitions to and from dyntick-idle mode, so that this counter
 has an even value when the CPU is in dyntick-idle mode and an odd
 value otherwise.
 
-</p><p>The <tt>-&gt;rcu_sched_qs_mask</tt> field is used
+</p><p>The <tt>-&gt;rcu_need_heavy_qs</tt> field is used
 to record the fact that the RCU core code would really like to
 see a quiescent state from the corresponding CPU, so much so that
 it is willing to call for heavy-weight dyntick-counter operations.
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index fbee1d729c4b..3c62ea06edb3 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -443,44 +443,14 @@ bool rcu_eqs_special_set(int cpu)
  * memory barriers to let the RCU core know about it, regardless of what
  * this CPU might (or might not) do in the near future.
  *
- * We inform the RCU core by emulating a zero-duration dyntick-idle
- * period, which we in turn do by incrementing the ->dynticks counter
- * by two.
+ * We inform the RCU core by emulating a zero-duration dyntick-idle period.
  *
  * The caller must have disabled interrupts.
  */
 static void rcu_momentary_dyntick_idle(void)
 {
-	struct rcu_data *rdp;
-	int resched_mask;
-	struct rcu_state *rsp;
-
-	/*
-	 * Yes, we can lose flag-setting operations.  This is OK, because
-	 * the flag will be set again after some delay.
-	 */
-	resched_mask = raw_cpu_read(rcu_dynticks.rcu_sched_qs_mask);
-	raw_cpu_write(rcu_dynticks.rcu_sched_qs_mask, 0);
-
-	/* Find the flavor that needs a quiescent state. */
-	for_each_rcu_flavor(rsp) {
-		rdp = raw_cpu_ptr(rsp->rda);
-		if (!(resched_mask & rsp->flavor_mask))
-			continue;
-		smp_mb(); /* rcu_sched_qs_mask before cond_resched_completed. */
-		if (READ_ONCE(rdp->mynode->completed) !=
-		    READ_ONCE(rdp->cond_resched_completed))
-			continue;
-
-		/*
-		 * Pretend to be momentarily idle for the quiescent state.
-		 * This allows the grace-period kthread to record the
-		 * quiescent state, with no need for this CPU to do anything
-		 * further.
-		 */
-		rcu_dynticks_momentary_idle();
-		break;
-	}
+	raw_cpu_write(rcu_dynticks.rcu_need_heavy_qs, false);
+	rcu_dynticks_momentary_idle();
 }
 
 /*
@@ -494,7 +464,7 @@ void rcu_note_context_switch(void)
 	trace_rcu_utilization(TPS("Start context switch"));
 	rcu_sched_qs();
 	rcu_preempt_note_context_switch();
-	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_sched_qs_mask)))
+	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs)))
 		rcu_momentary_dyntick_idle();
 	trace_rcu_utilization(TPS("End context switch"));
 	barrier(); /* Avoid RCU read-side critical sections leaking up. */
@@ -519,7 +489,7 @@ void rcu_all_qs(void)
 	unsigned long flags;
 
 	barrier(); /* Avoid RCU read-side critical sections leaking down. */
-	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_sched_qs_mask))) {
+	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs))) {
 		local_irq_save(flags);
 		rcu_momentary_dyntick_idle();
 		local_irq_restore(flags);
@@ -1275,7 +1245,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 				    bool *isidle, unsigned long *maxj)
 {
 	unsigned long jtsq;
-	int *rcrmp;
+	bool *rnhqp;
 	unsigned long rjtsc;
 	struct rcu_node *rnp;
 
@@ -1332,7 +1302,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 	 * in-kernel CPU-bound tasks cannot advance grace periods.
 	 * So if the grace period is old enough, make the CPU pay attention.
 	 * Note that the unsynchronized assignments to the per-CPU
-	 * rcu_sched_qs_mask variable are safe.  Yes, setting of
+	 * rcu_need_heavy_qs variable are safe.  Yes, setting of
 	 * bits can be lost, but they will be set again on the next
 	 * force-quiescent-state pass.  So lost bit sets do not result
 	 * in incorrect behavior, merely in a grace period lasting
@@ -1346,16 +1316,11 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 	 * is set too high, we override with half of the RCU CPU stall
 	 * warning delay.
 	 */
-	rcrmp = &per_cpu(rcu_dynticks.rcu_sched_qs_mask, rdp->cpu);
-	if (time_after(jiffies, rdp->rsp->gp_start + jtsq) ||
-	    time_after(jiffies, rdp->rsp->jiffies_resched)) {
-		if (!(READ_ONCE(*rcrmp) & rdp->rsp->flavor_mask)) {
-			WRITE_ONCE(rdp->cond_resched_completed,
-				   READ_ONCE(rdp->mynode->completed));
-			smp_mb(); /* ->cond_resched_completed before *rcrmp. */
-			WRITE_ONCE(*rcrmp,
-				   READ_ONCE(*rcrmp) + rdp->rsp->flavor_mask);
-		}
+	rnhqp = &per_cpu(rcu_dynticks.rcu_need_heavy_qs, rdp->cpu);
+	if (!READ_ONCE(*rnhqp) &&
+	    (time_after(jiffies, rdp->rsp->gp_start + jtsq) ||
+	     time_after(jiffies, rdp->rsp->jiffies_resched))) {
+		WRITE_ONCE(*rnhqp, true);
 		rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */
 	}
 
@@ -4169,7 +4134,6 @@ static void __init rcu_init_one(struct rcu_state *rsp)
 	static const char * const fqs[] = RCU_FQS_NAME_INIT;
 	static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
 	static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
-	static u8 fl_mask = 0x1;
 
 	int levelcnt[RCU_NUM_LVLS];		/* # nodes in each level. */
 	int levelspread[RCU_NUM_LVLS];		/* kids/node in each level. */
@@ -4191,8 +4155,6 @@ static void __init rcu_init_one(struct rcu_state *rsp)
 	for (i = 1; i < rcu_num_lvls; i++)
 		rsp->level[i] = rsp->level[i - 1] + levelcnt[i - 1];
 	rcu_init_levelspread(levelspread, levelcnt);
-	rsp->flavor_mask = fl_mask;
-	fl_mask <<= 1;
 
 	/* Initialize the elements themselves, starting from the leaves. */
 
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 76e4467bc765..b212cd0f22c7 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -113,7 +113,7 @@ struct rcu_dynticks {
 				    /* Process level is worth LLONG_MAX/2. */
 	int dynticks_nmi_nesting;   /* Track NMI nesting level. */
 	atomic_t dynticks;	    /* Even value for idle, else odd. */
-	int rcu_sched_qs_mask;      /* GP old, need heavy quiescent state. */
+	bool rcu_need_heavy_qs;      /* GP old, need heavy quiescent state. */
 	unsigned long rcu_qs_ctr;   /* Light universal quiescent state ctr. */
 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
 	long long dynticks_idle_nesting;
@@ -484,7 +484,6 @@ struct rcu_state {
 	struct rcu_node *level[RCU_NUM_LVLS + 1];
 						/* Hierarchy levels (+1 to */
 						/*  shut bogus gcc warning) */
-	u8 flavor_mask;				/* bit in flavor mask. */
 	struct rcu_data __percpu *rda;		/* pointer of percu rcu_data. */
 	call_rcu_func_t call;			/* call_rcu() flavor. */
 	int ncpus;				/* # CPUs seen so far. */
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 11/39] rcu: Place guard on rcu_all_qs() and rcu_note_context_switch() actions
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (9 preceding siblings ...)
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 10/39] rcu: Eliminate flavor scan in rcu_momentary_dyntick_idle() Paul E. McKenney
@ 2017-04-17 23:44   ` Paul E. McKenney
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 12/39] rcu: Default RCU_FANOUT_LEAF to 16 unless explicitly changed Paul E. McKenney
                     ` (28 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:44 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The rcu_all_qs() and rcu_note_context_switch() do a series of checks,
taking various actions to supply RCU with quiescent states, depending
on the outcomes of the various checks.  This is a bit much for scheduling
fastpaths, so this commit creates a separate ->rcu_urgent_qs field in
the rcu_dynticks structure that acts as a global guard for these checks.
Thus, in the common case, rcu_all_qs() and rcu_note_context_switch()
check the ->rcu_urgent_qs field, find it false, and simply return.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 .../Design/Data-Structures/Data-Structures.html    | 11 ++++++-
 kernel/rcu/tree.c                                  | 38 ++++++++++++++--------
 kernel/rcu/tree.h                                  |  3 +-
 kernel/rcu/tree_exp.h                              |  2 ++
 kernel/rcu/tree_plugin.h                           |  8 +++--
 5 files changed, 44 insertions(+), 18 deletions(-)

diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.html b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
index e4bf20a68fa3..4dec89097559 100644
--- a/Documentation/RCU/Design/Data-Structures/Data-Structures.html
+++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
@@ -1106,6 +1106,7 @@ Its fields are as follows:
   3   atomic_t dynticks;
   4   bool rcu_need_heavy_qs;
   5   unsigned long rcu_qs_ctr;
+  6   bool rcu_urgent_qs;
 </pre>
 
 <p>The <tt>-&gt;dynticks_nesting</tt> field counts the
@@ -1131,12 +1132,20 @@ it is willing to call for heavy-weight dyntick-counter operations.
 This flag is checked by RCU's context-switch and <tt>cond_resched()</tt>
 code, which provide a momentary idle sojourn in response.
 
-</p><p>Finally the <tt>-&gt;rcu_qs_ctr</tt> field is used to record
+</p><p>The <tt>-&gt;rcu_qs_ctr</tt> field is used to record
 quiescent states from <tt>cond_resched()</tt>.
 Because <tt>cond_resched()</tt> can execute quite frequently, this
 must be quite lightweight, as in a non-atomic increment of this
 per-CPU field.
 
+</p><p>Finally, the <tt>-&gt;rcu_urgent_qs</tt> field is used to record
+the fact that the RCU core code would really like to see a quiescent
+state from the corresponding CPU, with the various other fields indicating
+just how badly RCU wants this quiescent state.
+This flag is checked by RCU's context-switch and <tt>cond_resched()</tt>
+code, which, if nothing else, non-atomically increment <tt>-&gt;rcu_qs_ctr</tt>
+in response.
+
 <table>
 <tr><th>&nbsp;</th></tr>
 <tr><th align="left">Quick Quiz:</th></tr>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 3c62ea06edb3..aa81cc6c365e 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -464,8 +464,14 @@ void rcu_note_context_switch(void)
 	trace_rcu_utilization(TPS("Start context switch"));
 	rcu_sched_qs();
 	rcu_preempt_note_context_switch();
+	/* Load rcu_urgent_qs before other flags. */
+	if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs)))
+		goto out;
+	this_cpu_write(rcu_dynticks.rcu_urgent_qs, false);
 	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs)))
 		rcu_momentary_dyntick_idle();
+	this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
+out:
 	trace_rcu_utilization(TPS("End context switch"));
 	barrier(); /* Avoid RCU read-side critical sections leaking up. */
 }
@@ -488,29 +494,26 @@ void rcu_all_qs(void)
 {
 	unsigned long flags;
 
+	if (!raw_cpu_read(rcu_dynticks.rcu_urgent_qs))
+		return;
+	preempt_disable();
+	/* Load rcu_urgent_qs before other flags. */
+	if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs))) {
+		preempt_enable();
+		return;
+	}
+	this_cpu_write(rcu_dynticks.rcu_urgent_qs, false);
 	barrier(); /* Avoid RCU read-side critical sections leaking down. */
 	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs))) {
 		local_irq_save(flags);
 		rcu_momentary_dyntick_idle();
 		local_irq_restore(flags);
 	}
-	if (unlikely(raw_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))) {
-		/*
-		 * Yes, we just checked a per-CPU variable with preemption
-		 * enabled, so we might be migrated to some other CPU at
-		 * this point.  That is OK because in that case, the
-		 * migration will supply the needed quiescent state.
-		 * We might end up needlessly disabling preemption and
-		 * invoking rcu_sched_qs() on the destination CPU, but
-		 * the probability and cost are both quite low, so this
-		 * should not be a problem in practice.
-		 */
-		preempt_disable();
+	if (unlikely(raw_cpu_read(rcu_sched_data.cpu_no_qs.b.exp)))
 		rcu_sched_qs();
-		preempt_enable();
-	}
 	this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
 	barrier(); /* Avoid RCU read-side critical sections leaking up. */
+	preempt_enable();
 }
 EXPORT_SYMBOL_GPL(rcu_all_qs);
 
@@ -1246,6 +1249,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 {
 	unsigned long jtsq;
 	bool *rnhqp;
+	bool *ruqp;
 	unsigned long rjtsc;
 	struct rcu_node *rnp;
 
@@ -1281,11 +1285,15 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 	 * might not be the case for nohz_full CPUs looping in the kernel.
 	 */
 	rnp = rdp->mynode;
+	ruqp = per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, rdp->cpu);
 	if (time_after(jiffies, rdp->rsp->gp_start + jtsq) &&
 	    READ_ONCE(rdp->rcu_qs_ctr_snap) != per_cpu(rcu_dynticks.rcu_qs_ctr, rdp->cpu) &&
 	    READ_ONCE(rdp->gpnum) == rnp->gpnum && !rdp->gpwrap) {
 		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("rqc"));
 		return 1;
+	} else {
+		/* Load rcu_qs_ctr before store to rcu_urgent_qs. */
+		smp_store_release(ruqp, true);
 	}
 
 	/* Check for the CPU being offline. */
@@ -1321,6 +1329,8 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 	    (time_after(jiffies, rdp->rsp->gp_start + jtsq) ||
 	     time_after(jiffies, rdp->rsp->jiffies_resched))) {
 		WRITE_ONCE(*rnhqp, true);
+		/* Store rcu_need_heavy_qs before rcu_urgent_qs. */
+		smp_store_release(ruqp, true);
 		rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */
 	}
 
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index b212cd0f22c7..d2f276fc2edc 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -113,8 +113,9 @@ struct rcu_dynticks {
 				    /* Process level is worth LLONG_MAX/2. */
 	int dynticks_nmi_nesting;   /* Track NMI nesting level. */
 	atomic_t dynticks;	    /* Even value for idle, else odd. */
-	bool rcu_need_heavy_qs;      /* GP old, need heavy quiescent state. */
+	bool rcu_need_heavy_qs;     /* GP old, need heavy quiescent state. */
 	unsigned long rcu_qs_ctr;   /* Light universal quiescent state ctr. */
+	bool rcu_urgent_qs;	    /* GP old need light quiescent state. */
 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
 	long long dynticks_idle_nesting;
 				    /* irq/process nesting level from idle. */
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index a7b639ccd46e..a1f52bbe9db6 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -331,6 +331,8 @@ static void sync_sched_exp_handler(void *data)
 		return;
 	}
 	__this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, true);
+	/* Store .exp before .rcu_urgent_qs. */
+	smp_store_release(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs), true);
 	resched_cpu(smp_processor_id());
 }
 
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 0a62a8f1caac..621296a6694b 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1860,7 +1860,9 @@ static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
 			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
 					    TPS("WakeEmpty"));
 		} else {
-			rdp->nocb_defer_wakeup = RCU_NOGP_WAKE;
+			WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOGP_WAKE);
+			/* Store ->nocb_defer_wakeup before ->rcu_urgent_qs. */
+			smp_store_release(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs), true);
 			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
 					    TPS("WakeEmptyIsDeferred"));
 		}
@@ -1872,7 +1874,9 @@ static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
 			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
 					    TPS("WakeOvf"));
 		} else {
-			rdp->nocb_defer_wakeup = RCU_NOGP_WAKE_FORCE;
+			WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOGP_WAKE_FORCE);
+			/* Store ->nocb_defer_wakeup before ->rcu_urgent_qs. */
+			smp_store_release(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs), true);
 			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
 					    TPS("WakeOvfIsDeferred"));
 		}
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 12/39] rcu: Default RCU_FANOUT_LEAF to 16 unless explicitly changed
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (10 preceding siblings ...)
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 11/39] rcu: Place guard on rcu_all_qs() and rcu_note_context_switch() actions Paul E. McKenney
@ 2017-04-17 23:44   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 13/39] srcu: Abstract multi-tail callback list handling Paul E. McKenney
                     ` (27 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:44 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

If the RCU_EXPERT Kconfig option is not set (the default), then the
RCU_FANOUT_LEAF Kconfig option will not be defined, which will cause
the leaf-level rcu_node tree fanout to default to 32 on 32-bit systems
and 64 on 64-bit systems.  This can result in excessive lock contention.
This commit therefore changes the computation of the leaf-level rcu_node
tree fanout so that the result will be 16 unless an explicit Kconfig or
kernel-boot setting says otherwise.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.h | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index d2f276fc2edc..376c01e539c7 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -52,11 +52,7 @@
 #ifdef CONFIG_RCU_FANOUT_LEAF
 #define RCU_FANOUT_LEAF CONFIG_RCU_FANOUT_LEAF
 #else /* #ifdef CONFIG_RCU_FANOUT_LEAF */
-# ifdef CONFIG_64BIT
-# define RCU_FANOUT_LEAF 64
-# else
-# define RCU_FANOUT_LEAF 32
-# endif
+#define RCU_FANOUT_LEAF 16
 #endif /* #else #ifdef CONFIG_RCU_FANOUT_LEAF */
 
 #define RCU_FANOUT_1	      (RCU_FANOUT_LEAF)
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 13/39] srcu: Abstract multi-tail callback list handling
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (11 preceding siblings ...)
  2017-04-17 23:44   ` [PATCH v2 tip/core/rcu 12/39] rcu: Default RCU_FANOUT_LEAF to 16 unless explicitly changed Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 14/39] srcu: Allow SRCU to access rcu_scheduler_active Paul E. McKenney
                     ` (26 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

RCU has only one multi-tail callback list, which is implemented via
the nxtlist, nxttail, nxtcompleted, qlen_lazy, and qlen fields in the
rcu_data structure, and whose operations are open-code throughout the
Tree RCU implementation.  This has been more or less OK in the past,
but upcoming callback-list optimizations in SRCU could really use
a multi-tail callback list there as well.

This commit therefore abstracts the multi-tail callback list handling
into a new kernel/rcu/rcu_segcblist.h file, and uses this new API.
The simple head-and-tail pointer callback list is also abstracted and
applied everywhere except for the NOCB callback-offload lists.  (Yes,
the plan is to apply them there as well, but this commit is already
bigger than would be good.)

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcu_segcblist.h | 625 +++++++++++++++++++++++++++++++++++++++++++++
 kernel/rcu/tree.c          | 348 ++++++++-----------------
 kernel/rcu/tree.h          |  41 +--
 kernel/rcu/tree_plugin.h   |  54 ++--
 kernel/rcu/tree_trace.c    |  21 +-
 5 files changed, 780 insertions(+), 309 deletions(-)
 create mode 100644 kernel/rcu/rcu_segcblist.h

diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
new file mode 100644
index 000000000000..24078f3c0218
--- /dev/null
+++ b/kernel/rcu/rcu_segcblist.h
@@ -0,0 +1,625 @@
+/*
+ * RCU segmented callback lists
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright IBM Corporation, 2017
+ *
+ * Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ */
+
+#ifndef __KERNEL_RCU_SEGCBLIST_H
+#define __KERNEL_RCU_SEGCBLIST_H
+
+/* Simple unsegmented callback lists. */
+struct rcu_cblist {
+	struct rcu_head *head;
+	struct rcu_head **tail;
+	long len;
+	long len_lazy;
+};
+
+#define RCU_CBLIST_INITIALIZER(n) { .head = NULL, .tail = &n.head }
+
+/* Initialize simple callback list. */
+static inline void rcu_cblist_init(struct rcu_cblist *rclp)
+{
+	rclp->head = NULL;
+	rclp->tail = &rclp->head;
+	rclp->len = 0;
+	rclp->len_lazy = 0;
+}
+
+/* Is simple callback list empty? */
+static inline bool rcu_cblist_empty(struct rcu_cblist *rclp)
+{
+	return !rclp->head;
+}
+
+/* Return number of callbacks in simple callback list. */
+static inline long rcu_cblist_n_cbs(struct rcu_cblist *rclp)
+{
+	return rclp->len;
+}
+
+/* Return number of lazy callbacks in simple callback list. */
+static inline long rcu_cblist_n_lazy_cbs(struct rcu_cblist *rclp)
+{
+	return rclp->len_lazy;
+}
+
+/*
+ * Debug function to actually count the number of callbacks.
+ * If the number exceeds the limit specified, return -1.
+ */
+static inline long rcu_cblist_count_cbs(struct rcu_cblist *rclp, long lim)
+{
+	int cnt = 0;
+	struct rcu_head **rhpp = &rclp->head;
+
+	for (;;) {
+		if (!*rhpp)
+			return cnt;
+		if (++cnt > lim)
+			return -1;
+		rhpp = &(*rhpp)->next;
+	}
+}
+
+/*
+ * Dequeue the oldest rcu_head structure from the specified callback
+ * list.  This function assumes that the callback is non-lazy, but
+ * the caller can later invoke rcu_cblist_dequeued_lazy() if it
+ * finds otherwise (and if it cares about laziness).  This allows
+ * different users to have different ways of determining laziness.
+ */
+static inline struct rcu_head *rcu_cblist_dequeue(struct rcu_cblist *rclp)
+{
+	struct rcu_head *rhp;
+
+	rhp = rclp->head;
+	if (!rhp)
+		return NULL;
+	prefetch(rhp);
+	rclp->len--;
+	rclp->head = rhp->next;
+	if (!rclp->head)
+		rclp->tail = &rclp->head;
+	return rhp;
+}
+
+/*
+ * Account for the fact that a previously dequeued callback turned out
+ * to be marked as lazy.
+ */
+static inline void rcu_cblist_dequeued_lazy(struct rcu_cblist *rclp)
+{
+	rclp->len_lazy--;
+}
+
+/*
+ * Interim function to return rcu_cblist head pointer.  Longer term, the
+ * rcu_cblist will be used more pervasively, removing the need for this
+ * function.
+ */
+static inline struct rcu_head *rcu_cblist_head(struct rcu_cblist *rclp)
+{
+	return rclp->head;
+}
+
+/*
+ * Interim function to return rcu_cblist head pointer.  Longer term, the
+ * rcu_cblist will be used more pervasively, removing the need for this
+ * function.
+ */
+static inline struct rcu_head **rcu_cblist_tail(struct rcu_cblist *rclp)
+{
+	WARN_ON_ONCE(rcu_cblist_empty(rclp));
+	return rclp->tail;
+}
+
+/* Complicated segmented callback lists.  ;-) */
+
+/*
+ * Index values for segments in rcu_segcblist structure.
+ *
+ * The segments are as follows:
+ *
+ * [head, *tails[RCU_DONE_TAIL]):
+ *	Callbacks whose grace period has elapsed, and thus can be invoked.
+ * [*tails[RCU_DONE_TAIL], *tails[RCU_WAIT_TAIL]):
+ *	Callbacks waiting for the current GP from the current CPU's viewpoint.
+ * [*tails[RCU_WAIT_TAIL], *tails[RCU_NEXT_READY_TAIL]):
+ *	Callbacks that arrived before the next GP started, again from
+ *	the current CPU's viewpoint.  These can be handled by the next GP.
+ * [*tails[RCU_NEXT_READY_TAIL], *tails[RCU_NEXT_TAIL]):
+ *	Callbacks that might have arrived after the next GP started.
+ *	There is some uncertainty as to when a given GP starts and
+ *	ends, but a CPU knows the exact times if it is the one starting
+ *	or ending the GP.  Other CPUs know that the previous GP ends
+ *	before the next one starts.
+ *
+ * Note that RCU_WAIT_TAIL cannot be empty unless RCU_NEXT_READY_TAIL is also
+ * empty.
+ *
+ * The ->gp_seq[] array contains the grace-period number at which the
+ * corresponding segment of callbacks will be ready to invoke.  A given
+ * element of this array is meaningful only when the corresponding segment
+ * is non-empty, and it is never valid for RCU_DONE_TAIL (whose callbacks
+ * are already ready to invoke) or for RCU_NEXT_TAIL (whose callbacks have
+ * not yet been assigned a grace-period number).
+ */
+#define RCU_DONE_TAIL		0	/* Also RCU_WAIT head. */
+#define RCU_WAIT_TAIL		1	/* Also RCU_NEXT_READY head. */
+#define RCU_NEXT_READY_TAIL	2	/* Also RCU_NEXT head. */
+#define RCU_NEXT_TAIL		3
+#define RCU_CBLIST_NSEGS	4
+
+struct rcu_segcblist {
+	struct rcu_head *head;
+	struct rcu_head **tails[RCU_CBLIST_NSEGS];
+	unsigned long gp_seq[RCU_CBLIST_NSEGS];
+	long len;
+	long len_lazy;
+};
+
+/*
+ * Initialize an rcu_segcblist structure.
+ */
+static inline void rcu_segcblist_init(struct rcu_segcblist *rsclp)
+{
+	int i;
+
+	BUILD_BUG_ON(RCU_NEXT_TAIL + 1 != ARRAY_SIZE(rsclp->gp_seq));
+	BUILD_BUG_ON(ARRAY_SIZE(rsclp->tails) != ARRAY_SIZE(rsclp->gp_seq));
+	rsclp->head = NULL;
+	for (i = 0; i < RCU_CBLIST_NSEGS; i++)
+		rsclp->tails[i] = &rsclp->head;
+	rsclp->len = 0;
+	rsclp->len_lazy = 0;
+}
+
+/*
+ * Is the specified rcu_segcblist structure empty?
+ *
+ * But careful!  The fact that the ->head field is NULL does not
+ * necessarily imply that there are no callbacks associated with
+ * this structure.  When callbacks are being invoked, they are
+ * removed as a group.  If callback invocation must be preempted,
+ * the remaining callbacks will be added back to the list.  Either
+ * way, the counts are updated later.
+ *
+ * So it is often the case that rcu_segcblist_n_cbs() should be used
+ * instead.
+ */
+static inline bool rcu_segcblist_empty(struct rcu_segcblist *rsclp)
+{
+	return !rsclp->head;
+}
+
+/* Return number of callbacks in segmented callback list. */
+static inline long rcu_segcblist_n_cbs(struct rcu_segcblist *rsclp)
+{
+	return READ_ONCE(rsclp->len);
+}
+
+/* Return number of lazy callbacks in segmented callback list. */
+static inline long rcu_segcblist_n_lazy_cbs(struct rcu_segcblist *rsclp)
+{
+	return rsclp->len_lazy;
+}
+
+/* Return number of lazy callbacks in segmented callback list. */
+static inline long rcu_segcblist_n_nonlazy_cbs(struct rcu_segcblist *rsclp)
+{
+	return rsclp->len - rsclp->len_lazy;
+}
+
+/*
+ * Is the specified rcu_segcblist enabled, for example, not corresponding
+ * to an offline or callback-offloaded CPU?
+ */
+static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp)
+{
+	return !!rsclp->tails[RCU_NEXT_TAIL];
+}
+
+/*
+ * Disable the specified rcu_segcblist structure, so that callbacks can
+ * no longer be posted to it.  This structure must be empty.
+ */
+static inline void rcu_segcblist_disable(struct rcu_segcblist *rsclp)
+{
+	WARN_ON_ONCE(!rcu_segcblist_empty(rsclp));
+	WARN_ON_ONCE(rcu_segcblist_n_cbs(rsclp));
+	WARN_ON_ONCE(rcu_segcblist_n_lazy_cbs(rsclp));
+	rsclp->tails[RCU_NEXT_TAIL] = NULL;
+}
+
+/*
+ * Is the specified segment of the specified rcu_segcblist structure
+ * empty of callbacks?
+ */
+static inline bool rcu_segcblist_segempty(struct rcu_segcblist *rsclp, int seg)
+{
+	if (seg == RCU_DONE_TAIL)
+		return &rsclp->head == rsclp->tails[RCU_DONE_TAIL];
+	return rsclp->tails[seg - 1] == rsclp->tails[seg];
+}
+
+/*
+ * Are all segments following the specified segment of the specified
+ * rcu_segcblist structure empty of callbacks?  (The specified
+ * segment might well contain callbacks.)
+ */
+static inline bool rcu_segcblist_restempty(struct rcu_segcblist *rsclp, int seg)
+{
+	return !*rsclp->tails[seg];
+}
+
+/*
+ * Does the specified rcu_segcblist structure contain callbacks that
+ * are ready to be invoked?
+ */
+static inline bool rcu_segcblist_ready_cbs(struct rcu_segcblist *rsclp)
+{
+	return rcu_segcblist_is_enabled(rsclp) &&
+	       &rsclp->head != rsclp->tails[RCU_DONE_TAIL];
+}
+
+/*
+ * Does the specified rcu_segcblist structure contain callbacks that
+ * are still pending, that is, not yet ready to be invoked?
+ */
+static inline bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp)
+{
+	return rcu_segcblist_is_enabled(rsclp) &&
+	       !rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL);
+}
+
+/*
+ * Return a pointer to the first callback in the specified rcu_segcblist
+ * structure.  This is useful for diagnostics.
+ */
+static inline struct rcu_head *
+rcu_segcblist_first_cb(struct rcu_segcblist *rsclp)
+{
+	if (rcu_segcblist_is_enabled(rsclp))
+		return rsclp->head;
+	return NULL;
+}
+
+/*
+ * Return a pointer to the first pending callback in the specified
+ * rcu_segcblist structure.  This is useful just after posting a given
+ * callback -- if that callback is the first pending callback, then
+ * you cannot rely on someone else having already started up the required
+ * grace period.
+ */
+static inline struct rcu_head *
+rcu_segcblist_first_pend_cb(struct rcu_segcblist *rsclp)
+{
+	if (rcu_segcblist_is_enabled(rsclp))
+		return *rsclp->tails[RCU_DONE_TAIL];
+	return NULL;
+}
+
+/*
+ * Does the specified rcu_segcblist structure contain callbacks that
+ * have not yet been processed beyond having been posted, that is,
+ * does it contain callbacks in its last segment?
+ */
+static inline bool rcu_segcblist_new_cbs(struct rcu_segcblist *rsclp)
+{
+	return rcu_segcblist_is_enabled(rsclp) &&
+	       !rcu_segcblist_restempty(rsclp, RCU_NEXT_READY_TAIL);
+}
+
+/*
+ * Enqueue the specified callback onto the specified rcu_segcblist
+ * structure, updating accounting as needed.  Note that the ->len
+ * field may be accessed locklessly, hence the WRITE_ONCE().
+ * The ->len field is used by rcu_barrier() and friends to determine
+ * if it must post a callback on this structure, and it is OK
+ * for rcu_barrier() to sometimes post callbacks needlessly, but
+ * absolutely not OK for it to ever miss posting a callback.
+ */
+static inline void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
+					 struct rcu_head *rhp, bool lazy)
+{
+	WRITE_ONCE(rsclp->len, rsclp->len + 1); /* ->len sampled locklessly. */
+	if (lazy)
+		rsclp->len_lazy++;
+	smp_mb(); /* Ensure counts are updated before callback is enqueued. */
+	rhp->next = NULL;
+	*rsclp->tails[RCU_NEXT_TAIL] = rhp;
+	rsclp->tails[RCU_NEXT_TAIL] = &rhp->next;
+}
+
+/*
+ * Extract only the counts from the specified rcu_segcblist structure,
+ * and place them in the specified rcu_cblist structure.  This function
+ * supports both callback orphaning and invocation, hence the separation
+ * of counts and callbacks.  (Callbacks ready for invocation must be
+ * orphaned and adopted separately from pending callbacks, but counts
+ * apply to all callbacks.  Locking must be used to make sure that
+ * both orphaned-callbacks lists are consistent.)
+ */
+static inline void rcu_segcblist_extract_count(struct rcu_segcblist *rsclp,
+					       struct rcu_cblist *rclp)
+{
+	rclp->len_lazy += rsclp->len_lazy;
+	rclp->len += rsclp->len;
+	rsclp->len_lazy = 0;
+	WRITE_ONCE(rsclp->len, 0); /* ->len sampled locklessly. */
+}
+
+/*
+ * Extract only those callbacks ready to be invoked from the specified
+ * rcu_segcblist structure and place them in the specified rcu_cblist
+ * structure.
+ */
+static inline void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp,
+						  struct rcu_cblist *rclp)
+{
+	int i;
+
+	if (!rcu_segcblist_ready_cbs(rsclp))
+		return; /* Nothing to do. */
+	*rclp->tail = rsclp->head;
+	rsclp->head = *rsclp->tails[RCU_DONE_TAIL];
+	*rsclp->tails[RCU_DONE_TAIL] = NULL;
+	rclp->tail = rsclp->tails[RCU_DONE_TAIL];
+	for (i = RCU_CBLIST_NSEGS - 1; i >= RCU_DONE_TAIL; i--)
+		if (rsclp->tails[i] == rsclp->tails[RCU_DONE_TAIL])
+			rsclp->tails[i] = &rsclp->head;
+}
+
+/*
+ * Extract only those callbacks still pending (not yet ready to be
+ * invoked) from the specified rcu_segcblist structure and place them in
+ * the specified rcu_cblist structure.  Note that this loses information
+ * about any callbacks that might have been partway done waiting for
+ * their grace period.  Too bad!  They will have to start over.
+ */
+static inline void
+rcu_segcblist_extract_pend_cbs(struct rcu_segcblist *rsclp,
+			       struct rcu_cblist *rclp)
+{
+	int i;
+
+	if (!rcu_segcblist_pend_cbs(rsclp))
+		return; /* Nothing to do. */
+	*rclp->tail = *rsclp->tails[RCU_DONE_TAIL];
+	rclp->tail = rsclp->tails[RCU_NEXT_TAIL];
+	*rsclp->tails[RCU_DONE_TAIL] = NULL;
+	for (i = RCU_DONE_TAIL + 1; i < RCU_CBLIST_NSEGS; i++)
+		rsclp->tails[i] = rsclp->tails[RCU_DONE_TAIL];
+}
+
+/*
+ * Move the entire contents of the specified rcu_segcblist structure,
+ * counts, callbacks, and all, to the specified rcu_cblist structure.
+ * @@@ Why do we need this???  Moving early-boot CBs to NOCB lists?
+ * @@@ Memory barrier needed?  (Not if only used at boot time...)
+ */
+static inline void rcu_segcblist_extract_all(struct rcu_segcblist *rsclp,
+					     struct rcu_cblist *rclp)
+{
+	rcu_segcblist_extract_done_cbs(rsclp, rclp);
+	rcu_segcblist_extract_pend_cbs(rsclp, rclp);
+	rcu_segcblist_extract_count(rsclp, rclp);
+}
+
+/*
+ * Insert counts from the specified rcu_cblist structure in the
+ * specified rcu_segcblist structure.
+ */
+static inline void rcu_segcblist_insert_count(struct rcu_segcblist *rsclp,
+					      struct rcu_cblist *rclp)
+{
+	rsclp->len_lazy += rclp->len_lazy;
+	/* ->len sampled locklessly. */
+	WRITE_ONCE(rsclp->len, rsclp->len + rclp->len);
+	rclp->len_lazy = 0;
+	rclp->len = 0;
+}
+
+/*
+ * Move callbacks from the specified rcu_cblist to the beginning of the
+ * done-callbacks segment of the specified rcu_segcblist.
+ */
+static inline void rcu_segcblist_insert_done_cbs(struct rcu_segcblist *rsclp,
+						 struct rcu_cblist *rclp)
+{
+	int i;
+
+	if (!rclp->head)
+		return; /* No callbacks to move. */
+	*rclp->tail = rsclp->head;
+	rsclp->head = rclp->head;
+	for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++)
+		if (&rsclp->head == rsclp->tails[i])
+			rsclp->tails[i] = rclp->tail;
+		else
+			break;
+	rclp->head = NULL;
+	rclp->tail = &rclp->head;
+}
+
+/*
+ * Move callbacks from the specified rcu_cblist to the end of the
+ * new-callbacks segment of the specified rcu_segcblist.
+ */
+static inline void rcu_segcblist_insert_pend_cbs(struct rcu_segcblist *rsclp,
+						 struct rcu_cblist *rclp)
+{
+	if (!rclp->head)
+		return; /* Nothing to do. */
+	*rsclp->tails[RCU_NEXT_TAIL] = rclp->head;
+	rsclp->tails[RCU_NEXT_TAIL] = rclp->tail;
+	rclp->head = NULL;
+	rclp->tail = &rclp->head;
+}
+
+/*
+ * Advance the callbacks in the specified rcu_segcblist structure based
+ * on the current value passed in for the grace-period counter.
+ */
+static inline void rcu_segcblist_advance(struct rcu_segcblist *rsclp,
+					 unsigned long seq)
+{
+	int i, j;
+
+	WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
+	WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL));
+
+	/*
+	 * Find all callbacks whose ->gp_seq numbers indicate that they
+	 * are ready to invoke, and put them into the RCU_DONE_TAIL segment.
+	 */
+	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
+		if (ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
+			break;
+		rsclp->tails[RCU_DONE_TAIL] = rsclp->tails[i];
+	}
+
+	/* If no callbacks moved, nothing more need be done. */
+	if (i == RCU_WAIT_TAIL)
+		return;
+
+	/* Clean up tail pointers that might have been misordered above. */
+	for (j = RCU_WAIT_TAIL; j < i; j++)
+		rsclp->tails[j] = rsclp->tails[RCU_DONE_TAIL];
+
+	/*
+	 * Callbacks moved, so clean up the misordered ->tails[] pointers
+	 * that now point into the middle of the list of ready-to-invoke
+	 * callbacks.  The overall effect is to copy down the later pointers
+	 * into the gap that was created by the now-ready segments.
+	 */
+	for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
+		if (rsclp->tails[j] == rsclp->tails[RCU_NEXT_TAIL])
+			break;  /* No more callbacks. */
+		rsclp->tails[j] = rsclp->tails[i];
+		rsclp->gp_seq[j] = rsclp->gp_seq[i];
+	}
+}
+
+/*
+ * "Accelerate" callbacks based on more-accurate grace-period information.
+ * The reason for this is that RCU does not synchronize the beginnings and
+ * ends of grace periods, and that callbacks are posted locally.  This in
+ * turn means that the callbacks must be labelled conservatively early
+ * on, as getting exact information would degrade both performance and
+ * scalability.  When more accurate grace-period information becomes
+ * available, previously posted callbacks can be "accelerated", marking
+ * them to complete at the end of the earlier grace period.
+ *
+ * This function operates on an rcu_segcblist structure, and also the
+ * grace-period sequence number at which new callbacks would become
+ * ready to invoke.
+ */
+static inline bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp,
+					    unsigned long seq)
+{
+	int i;
+
+	WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
+	WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL));
+
+	/*
+	 * Find the segment preceding the oldest segment of callbacks
+	 * whose ->gp_seq[] completion is at or after that passed in via
+	 * "seq", skipping any empty segments.  This oldest segment, along
+	 * with any later segments, can be merged in with any newly arrived
+	 * callbacks in the RCU_NEXT_TAIL segment, and assigned "seq"
+	 * as their ->gp_seq[] grace-period completion sequence number.
+	 */
+	for (i = RCU_NEXT_READY_TAIL; i > RCU_DONE_TAIL; i--)
+		if (rsclp->tails[i] != rsclp->tails[i - 1] &&
+		    ULONG_CMP_LT(rsclp->gp_seq[i], seq))
+			break;
+
+	/*
+	 * If all the segments contain callbacks that correspond to
+	 * earlier grace-period sequence numbers than "seq", leave.
+	 * Assuming that the rcu_segcblist structure has enough
+	 * segments in its arrays, this can only happen if some of
+	 * the non-done segments contain callbacks that really are
+	 * ready to invoke.  This situation will get straightened
+	 * out by the next call to rcu_segcblist_advance().
+	 *
+	 * Also advance to the oldest segment of callbacks whose
+	 * ->gp_seq[] completion is at or after that passed in via "seq",
+	 * skipping any empty segments.
+	 */
+	if (++i >= RCU_NEXT_TAIL)
+		return false;
+
+	/*
+	 * Merge all later callbacks, including newly arrived callbacks,
+	 * into the segment located by the for-loop above.  Assign "seq"
+	 * as the ->gp_seq[] value in order to correctly handle the case
+	 * where there were no pending callbacks in the rcu_segcblist
+	 * structure other than in the RCU_NEXT_TAIL segment.
+	 */
+	for (; i < RCU_NEXT_TAIL; i++) {
+		rsclp->tails[i] = rsclp->tails[RCU_NEXT_TAIL];
+		rsclp->gp_seq[i] = seq;
+	}
+	return true;
+}
+
+/*
+ * Scan the specified rcu_segcblist structure for callbacks that need
+ * a grace period later than the one specified by "seq".  We don't look
+ * at the RCU_DONE_TAIL or RCU_NEXT_TAIL segments because they don't
+ * have a grace-period sequence number.
+ */
+static inline bool rcu_segcblist_future_gp_needed(struct rcu_segcblist *rsclp,
+						  unsigned long seq)
+{
+	int i;
+
+	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
+		if (rsclp->tails[i - 1] != rsclp->tails[i] &&
+		    ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
+			return true;
+	return false;
+}
+
+/*
+ * Interim function to return rcu_segcblist head pointer.  Longer term, the
+ * rcu_segcblist will be used more pervasively, removing the need for this
+ * function.
+ */
+static inline struct rcu_head *rcu_segcblist_head(struct rcu_segcblist *rsclp)
+{
+	return rsclp->head;
+}
+
+/*
+ * Interim function to return rcu_segcblist head pointer.  Longer term, the
+ * rcu_segcblist will be used more pervasively, removing the need for this
+ * function.
+ */
+static inline struct rcu_head **rcu_segcblist_tail(struct rcu_segcblist *rsclp)
+{
+	WARN_ON_ONCE(rcu_segcblist_empty(rsclp));
+	return rsclp->tails[RCU_NEXT_TAIL];
+}
+
+#endif /* __KERNEL_RCU_SEGCBLIST_H */
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index aa81cc6c365e..ea14e6410cb8 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -97,8 +97,8 @@ struct rcu_state sname##_state = { \
 	.gpnum = 0UL - 300UL, \
 	.completed = 0UL - 300UL, \
 	.orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
-	.orphan_nxttail = &sname##_state.orphan_nxtlist, \
-	.orphan_donetail = &sname##_state.orphan_donelist, \
+	.orphan_pend = RCU_CBLIST_INITIALIZER(sname##_state.orphan_pend), \
+	.orphan_done = RCU_CBLIST_INITIALIZER(sname##_state.orphan_done), \
 	.barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
 	.name = RCU_STATE_NAME(sname), \
 	.abbr = sabbr, \
@@ -726,16 +726,6 @@ void rcutorture_record_progress(unsigned long vernum)
 EXPORT_SYMBOL_GPL(rcutorture_record_progress);
 
 /*
- * Does the CPU have callbacks ready to be invoked?
- */
-static int
-cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
-{
-	return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] &&
-	       rdp->nxttail[RCU_NEXT_TAIL] != NULL;
-}
-
-/*
  * Return the root node of the specified rcu_state structure.
  */
 static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
@@ -765,21 +755,17 @@ static int rcu_future_needs_gp(struct rcu_state *rsp)
 static bool
 cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
 {
-	int i;
-
 	if (rcu_gp_in_progress(rsp))
 		return false;  /* No, a grace period is already in progress. */
 	if (rcu_future_needs_gp(rsp))
 		return true;  /* Yes, a no-CBs CPU needs one. */
-	if (!rdp->nxttail[RCU_NEXT_TAIL])
+	if (!rcu_segcblist_is_enabled(&rdp->cblist))
 		return false;  /* No, this is a no-CBs (or offline) CPU. */
-	if (*rdp->nxttail[RCU_NEXT_READY_TAIL])
+	if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
 		return true;  /* Yes, CPU has newly registered callbacks. */
-	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
-		if (rdp->nxttail[i - 1] != rdp->nxttail[i] &&
-		    ULONG_CMP_LT(READ_ONCE(rsp->completed),
-				 rdp->nxtcompleted[i]))
-			return true;  /* Yes, CBs for future grace period. */
+	if (rcu_segcblist_future_gp_needed(&rdp->cblist,
+					   READ_ONCE(rsp->completed)))
+		return true;  /* Yes, CBs for future grace period. */
 	return false; /* No grace period needed. */
 }
 
@@ -1490,7 +1476,8 @@ static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
 
 	print_cpu_stall_info_end();
 	for_each_possible_cpu(cpu)
-		totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
+		totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
+							    cpu)->cblist);
 	pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n",
 	       smp_processor_id(), (long)(jiffies - rsp->gp_start),
 	       (long)rsp->gpnum, (long)rsp->completed, totqlen);
@@ -1544,7 +1531,8 @@ static void print_cpu_stall(struct rcu_state *rsp)
 	print_cpu_stall_info(rsp, smp_processor_id());
 	print_cpu_stall_info_end();
 	for_each_possible_cpu(cpu)
-		totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
+		totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
+							    cpu)->cblist);
 	pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
 		jiffies - rsp->gp_start,
 		(long)rsp->gpnum, (long)rsp->completed, totqlen);
@@ -1647,30 +1635,6 @@ void rcu_cpu_stall_reset(void)
 }
 
 /*
- * Initialize the specified rcu_data structure's default callback list
- * to empty.  The default callback list is the one that is not used by
- * no-callbacks CPUs.
- */
-static void init_default_callback_list(struct rcu_data *rdp)
-{
-	int i;
-
-	rdp->nxtlist = NULL;
-	for (i = 0; i < RCU_NEXT_SIZE; i++)
-		rdp->nxttail[i] = &rdp->nxtlist;
-}
-
-/*
- * Initialize the specified rcu_data structure's callback list to empty.
- */
-static void init_callback_list(struct rcu_data *rdp)
-{
-	if (init_nocb_callback_list(rdp))
-		return;
-	init_default_callback_list(rdp);
-}
-
-/*
  * Determine the value that ->completed will have at the end of the
  * next subsequent grace period.  This is used to tag callbacks so that
  * a CPU can invoke callbacks in a timely fashion even if that CPU has
@@ -1724,7 +1688,6 @@ rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
 		    unsigned long *c_out)
 {
 	unsigned long c;
-	int i;
 	bool ret = false;
 	struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
 
@@ -1770,13 +1733,11 @@ rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
 	/*
 	 * Get a new grace-period number.  If there really is no grace
 	 * period in progress, it will be smaller than the one we obtained
-	 * earlier.  Adjust callbacks as needed.  Note that even no-CBs
-	 * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed.
+	 * earlier.  Adjust callbacks as needed.
 	 */
 	c = rcu_cbs_completed(rdp->rsp, rnp_root);
-	for (i = RCU_DONE_TAIL; i < RCU_NEXT_TAIL; i++)
-		if (ULONG_CMP_LT(c, rdp->nxtcompleted[i]))
-			rdp->nxtcompleted[i] = c;
+	if (!rcu_is_nocb_cpu(rdp->cpu))
+		(void)rcu_segcblist_accelerate(&rdp->cblist, c);
 
 	/*
 	 * If the needed for the required grace period is already
@@ -1856,57 +1817,27 @@ static void rcu_gp_kthread_wake(struct rcu_state *rsp)
 static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
 			       struct rcu_data *rdp)
 {
-	unsigned long c;
-	int i;
-	bool ret;
-
-	/* If the CPU has no callbacks, nothing to do. */
-	if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
-		return false;
-
-	/*
-	 * Starting from the sublist containing the callbacks most
-	 * recently assigned a ->completed number and working down, find the
-	 * first sublist that is not assignable to an upcoming grace period.
-	 * Such a sublist has something in it (first two tests) and has
-	 * a ->completed number assigned that will complete sooner than
-	 * the ->completed number for newly arrived callbacks (last test).
-	 *
-	 * The key point is that any later sublist can be assigned the
-	 * same ->completed number as the newly arrived callbacks, which
-	 * means that the callbacks in any of these later sublist can be
-	 * grouped into a single sublist, whether or not they have already
-	 * been assigned a ->completed number.
-	 */
-	c = rcu_cbs_completed(rsp, rnp);
-	for (i = RCU_NEXT_TAIL - 1; i > RCU_DONE_TAIL; i--)
-		if (rdp->nxttail[i] != rdp->nxttail[i - 1] &&
-		    !ULONG_CMP_GE(rdp->nxtcompleted[i], c))
-			break;
+	bool ret = false;
 
-	/*
-	 * If there are no sublist for unassigned callbacks, leave.
-	 * At the same time, advance "i" one sublist, so that "i" will
-	 * index into the sublist where all the remaining callbacks should
-	 * be grouped into.
-	 */
-	if (++i >= RCU_NEXT_TAIL)
+	/* If no pending (not yet ready to invoke) callbacks, nothing to do. */
+	if (!rcu_segcblist_pend_cbs(&rdp->cblist))
 		return false;
 
 	/*
-	 * Assign all subsequent callbacks' ->completed number to the next
-	 * full grace period and group them all in the sublist initially
-	 * indexed by "i".
+	 * Callbacks are often registered with incomplete grace-period
+	 * information.  Something about the fact that getting exact
+	 * information requires acquiring a global lock...  RCU therefore
+	 * makes a conservative estimate of the grace period number at which
+	 * a given callback will become ready to invoke.	The following
+	 * code checks this estimate and improves it when possible, thus
+	 * accelerating callback invocation to an earlier grace-period
+	 * number.
 	 */
-	for (; i <= RCU_NEXT_TAIL; i++) {
-		rdp->nxttail[i] = rdp->nxttail[RCU_NEXT_TAIL];
-		rdp->nxtcompleted[i] = c;
-	}
-	/* Record any needed additional grace periods. */
-	ret = rcu_start_future_gp(rnp, rdp, NULL);
+	if (rcu_segcblist_accelerate(&rdp->cblist, rcu_cbs_completed(rsp, rnp)))
+		ret = rcu_start_future_gp(rnp, rdp, NULL);
 
 	/* Trace depending on how much we were able to accelerate. */
-	if (!*rdp->nxttail[RCU_WAIT_TAIL])
+	if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
 		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB"));
 	else
 		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB"));
@@ -1926,32 +1857,15 @@ static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
 static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
 			    struct rcu_data *rdp)
 {
-	int i, j;
-
-	/* If the CPU has no callbacks, nothing to do. */
-	if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
+	/* If no pending (not yet ready to invoke) callbacks, nothing to do. */
+	if (!rcu_segcblist_pend_cbs(&rdp->cblist))
 		return false;
 
 	/*
 	 * Find all callbacks whose ->completed numbers indicate that they
 	 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
 	 */
-	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
-		if (ULONG_CMP_LT(rnp->completed, rdp->nxtcompleted[i]))
-			break;
-		rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[i];
-	}
-	/* Clean up any sublist tail pointers that were misordered above. */
-	for (j = RCU_WAIT_TAIL; j < i; j++)
-		rdp->nxttail[j] = rdp->nxttail[RCU_DONE_TAIL];
-
-	/* Copy down callbacks to fill in empty sublists. */
-	for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
-		if (rdp->nxttail[j] == rdp->nxttail[RCU_NEXT_TAIL])
-			break;
-		rdp->nxttail[j] = rdp->nxttail[i];
-		rdp->nxtcompleted[j] = rdp->nxtcompleted[i];
-	}
+	rcu_segcblist_advance(&rdp->cblist, rnp->completed);
 
 	/* Classify any remaining callbacks. */
 	return rcu_accelerate_cbs(rsp, rnp, rdp);
@@ -2668,13 +2582,8 @@ rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
 	 * because _rcu_barrier() excludes CPU-hotplug operations, so it
 	 * cannot be running now.  Thus no memory barrier is required.
 	 */
-	if (rdp->nxtlist != NULL) {
-		rsp->qlen_lazy += rdp->qlen_lazy;
-		rsp->qlen += rdp->qlen;
-		rdp->n_cbs_orphaned += rdp->qlen;
-		rdp->qlen_lazy = 0;
-		WRITE_ONCE(rdp->qlen, 0);
-	}
+	rdp->n_cbs_orphaned += rcu_segcblist_n_cbs(&rdp->cblist);
+	rcu_segcblist_extract_count(&rdp->cblist, &rsp->orphan_done);
 
 	/*
 	 * Next, move those callbacks still needing a grace period to
@@ -2682,31 +2591,18 @@ rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
 	 * Some of the callbacks might have gone partway through a grace
 	 * period, but that is too bad.  They get to start over because we
 	 * cannot assume that grace periods are synchronized across CPUs.
-	 * We don't bother updating the ->nxttail[] array yet, instead
-	 * we just reset the whole thing later on.
 	 */
-	if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) {
-		*rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL];
-		rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL];
-		*rdp->nxttail[RCU_DONE_TAIL] = NULL;
-	}
+	rcu_segcblist_extract_pend_cbs(&rdp->cblist, &rsp->orphan_pend);
 
 	/*
 	 * Then move the ready-to-invoke callbacks to the orphanage,
 	 * where some other CPU will pick them up.  These will not be
 	 * required to pass though another grace period: They are done.
 	 */
-	if (rdp->nxtlist != NULL) {
-		*rsp->orphan_donetail = rdp->nxtlist;
-		rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
-	}
+	rcu_segcblist_extract_done_cbs(&rdp->cblist, &rsp->orphan_done);
 
-	/*
-	 * Finally, initialize the rcu_data structure's list to empty and
-	 * disallow further callbacks on this CPU.
-	 */
-	init_callback_list(rdp);
-	rdp->nxttail[RCU_NEXT_TAIL] = NULL;
+	/* Finally, disallow further callbacks on this CPU.  */
+	rcu_segcblist_disable(&rdp->cblist);
 }
 
 /*
@@ -2715,7 +2611,6 @@ rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
  */
 static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
 {
-	int i;
 	struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
 
 	/* No-CBs CPUs are handled specially. */
@@ -2724,13 +2619,11 @@ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
 		return;
 
 	/* Do the accounting first. */
-	rdp->qlen_lazy += rsp->qlen_lazy;
-	rdp->qlen += rsp->qlen;
-	rdp->n_cbs_adopted += rsp->qlen;
-	if (rsp->qlen_lazy != rsp->qlen)
+	rdp->n_cbs_adopted += rcu_cblist_n_cbs(&rsp->orphan_done);
+	if (rcu_cblist_n_lazy_cbs(&rsp->orphan_done) !=
+	    rcu_cblist_n_cbs(&rsp->orphan_done))
 		rcu_idle_count_callbacks_posted();
-	rsp->qlen_lazy = 0;
-	rsp->qlen = 0;
+	rcu_segcblist_insert_count(&rdp->cblist, &rsp->orphan_done);
 
 	/*
 	 * We do not need a memory barrier here because the only way we
@@ -2738,24 +2631,13 @@ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
 	 * we are the task doing the rcu_barrier().
 	 */
 
-	/* First adopt the ready-to-invoke callbacks. */
-	if (rsp->orphan_donelist != NULL) {
-		*rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL];
-		*rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist;
-		for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--)
-			if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
-				rdp->nxttail[i] = rsp->orphan_donetail;
-		rsp->orphan_donelist = NULL;
-		rsp->orphan_donetail = &rsp->orphan_donelist;
-	}
-
-	/* And then adopt the callbacks that still need a grace period. */
-	if (rsp->orphan_nxtlist != NULL) {
-		*rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist;
-		rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail;
-		rsp->orphan_nxtlist = NULL;
-		rsp->orphan_nxttail = &rsp->orphan_nxtlist;
-	}
+	/* First adopt the ready-to-invoke callbacks, then the done ones. */
+	rcu_segcblist_insert_done_cbs(&rdp->cblist, &rsp->orphan_done);
+	WARN_ON_ONCE(!rcu_cblist_empty(&rsp->orphan_done));
+	rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rsp->orphan_pend);
+	WARN_ON_ONCE(!rcu_cblist_empty(&rsp->orphan_pend));
+	WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) !=
+		     !rcu_segcblist_n_cbs(&rdp->cblist));
 }
 
 /*
@@ -2843,9 +2725,11 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
 	rcu_adopt_orphan_cbs(rsp, flags);
 	raw_spin_unlock_irqrestore(&rsp->orphan_lock, flags);
 
-	WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
-		  "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
-		  cpu, rdp->qlen, rdp->nxtlist);
+	WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
+		  !rcu_segcblist_empty(&rdp->cblist),
+		  "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
+		  cpu, rcu_segcblist_n_cbs(&rdp->cblist),
+		  rcu_segcblist_first_cb(&rdp->cblist));
 }
 
 /*
@@ -2855,14 +2739,17 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
 static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
 {
 	unsigned long flags;
-	struct rcu_head *next, *list, **tail;
-	long bl, count, count_lazy;
-	int i;
+	struct rcu_head *rhp;
+	struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
+	long bl, count;
 
 	/* If no callbacks are ready, just return. */
-	if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
-		trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
-		trace_rcu_batch_end(rsp->name, 0, !!READ_ONCE(rdp->nxtlist),
+	if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
+		trace_rcu_batch_start(rsp->name,
+				      rcu_segcblist_n_lazy_cbs(&rdp->cblist),
+				      rcu_segcblist_n_cbs(&rdp->cblist), 0);
+		trace_rcu_batch_end(rsp->name, 0,
+				    !rcu_segcblist_empty(&rdp->cblist),
 				    need_resched(), is_idle_task(current),
 				    rcu_is_callbacks_kthread());
 		return;
@@ -2870,73 +2757,62 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
 
 	/*
 	 * Extract the list of ready callbacks, disabling to prevent
-	 * races with call_rcu() from interrupt handlers.
+	 * races with call_rcu() from interrupt handlers.  Leave the
+	 * callback counts, as rcu_barrier() needs to be conservative.
 	 */
 	local_irq_save(flags);
 	WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
 	bl = rdp->blimit;
-	trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
-	list = rdp->nxtlist;
-	rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
-	*rdp->nxttail[RCU_DONE_TAIL] = NULL;
-	tail = rdp->nxttail[RCU_DONE_TAIL];
-	for (i = RCU_NEXT_SIZE - 1; i >= 0; i--)
-		if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
-			rdp->nxttail[i] = &rdp->nxtlist;
+	trace_rcu_batch_start(rsp->name, rcu_segcblist_n_lazy_cbs(&rdp->cblist),
+			      rcu_segcblist_n_cbs(&rdp->cblist), bl);
+	rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
 	local_irq_restore(flags);
 
 	/* Invoke callbacks. */
-	count = count_lazy = 0;
-	while (list) {
-		next = list->next;
-		prefetch(next);
-		debug_rcu_head_unqueue(list);
-		if (__rcu_reclaim(rsp->name, list))
-			count_lazy++;
-		list = next;
-		/* Stop only if limit reached and CPU has something to do. */
-		if (++count >= bl &&
+	rhp = rcu_cblist_dequeue(&rcl);
+	for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
+		debug_rcu_head_unqueue(rhp);
+		if (__rcu_reclaim(rsp->name, rhp))
+			rcu_cblist_dequeued_lazy(&rcl);
+		/*
+		 * Stop only if limit reached and CPU has something to do.
+		 * Note: The rcl structure counts down from zero.
+		 */
+		if (-rcu_cblist_n_cbs(&rcl) >= bl &&
 		    (need_resched() ||
 		     (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
 			break;
 	}
 
 	local_irq_save(flags);
-	trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
-			    is_idle_task(current),
+	count = -rcu_cblist_n_cbs(&rcl);
+	trace_rcu_batch_end(rsp->name, count, !rcu_cblist_empty(&rcl),
+			    need_resched(), is_idle_task(current),
 			    rcu_is_callbacks_kthread());
 
-	/* Update count, and requeue any remaining callbacks. */
-	if (list != NULL) {
-		*tail = rdp->nxtlist;
-		rdp->nxtlist = list;
-		for (i = 0; i < RCU_NEXT_SIZE; i++)
-			if (&rdp->nxtlist == rdp->nxttail[i])
-				rdp->nxttail[i] = tail;
-			else
-				break;
-	}
+	/* Update counts and requeue any remaining callbacks. */
+	rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
 	smp_mb(); /* List handling before counting for rcu_barrier(). */
-	rdp->qlen_lazy -= count_lazy;
-	WRITE_ONCE(rdp->qlen, rdp->qlen - count);
 	rdp->n_cbs_invoked += count;
+	rcu_segcblist_insert_count(&rdp->cblist, &rcl);
 
 	/* Reinstate batch limit if we have worked down the excess. */
-	if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
+	count = rcu_segcblist_n_cbs(&rdp->cblist);
+	if (rdp->blimit == LONG_MAX && count <= qlowmark)
 		rdp->blimit = blimit;
 
 	/* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
-	if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
+	if (count == 0 && rdp->qlen_last_fqs_check != 0) {
 		rdp->qlen_last_fqs_check = 0;
 		rdp->n_force_qs_snap = rsp->n_force_qs;
-	} else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
-		rdp->qlen_last_fqs_check = rdp->qlen;
-	WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));
+	} else if (count < rdp->qlen_last_fqs_check - qhimark)
+		rdp->qlen_last_fqs_check = count;
+	WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) != (count == 0));
 
 	local_irq_restore(flags);
 
 	/* Re-invoke RCU core processing if there are callbacks remaining. */
-	if (cpu_has_callbacks_ready_to_invoke(rdp))
+	if (rcu_segcblist_ready_cbs(&rdp->cblist))
 		invoke_rcu_core();
 }
 
@@ -3120,7 +2996,7 @@ __rcu_process_callbacks(struct rcu_state *rsp)
 	}
 
 	/* If there are callbacks ready, invoke them. */
-	if (cpu_has_callbacks_ready_to_invoke(rdp))
+	if (rcu_segcblist_ready_cbs(&rdp->cblist))
 		invoke_rcu_callbacks(rsp, rdp);
 
 	/* Do any needed deferred wakeups of rcuo kthreads. */
@@ -3192,7 +3068,8 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
 	 * invoking force_quiescent_state() if the newly enqueued callback
 	 * is the only one waiting for a grace period to complete.
 	 */
-	if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
+	if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
+		     rdp->qlen_last_fqs_check + qhimark)) {
 
 		/* Are we ignoring a completed grace period? */
 		note_gp_changes(rsp, rdp);
@@ -3210,10 +3087,10 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
 			/* Give the grace period a kick. */
 			rdp->blimit = LONG_MAX;
 			if (rsp->n_force_qs == rdp->n_force_qs_snap &&
-			    *rdp->nxttail[RCU_DONE_TAIL] != head)
+			    rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
 				force_quiescent_state(rsp);
 			rdp->n_force_qs_snap = rsp->n_force_qs;
-			rdp->qlen_last_fqs_check = rdp->qlen;
+			rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
 		}
 	}
 }
@@ -3253,7 +3130,7 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func,
 	rdp = this_cpu_ptr(rsp->rda);
 
 	/* Add the callback to our list. */
-	if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL) || cpu != -1) {
+	if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist)) || cpu != -1) {
 		int offline;
 
 		if (cpu != -1)
@@ -3272,23 +3149,21 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func,
 		 */
 		BUG_ON(cpu != -1);
 		WARN_ON_ONCE(!rcu_is_watching());
-		if (!likely(rdp->nxtlist))
-			init_default_callback_list(rdp);
+		if (rcu_segcblist_empty(&rdp->cblist))
+			rcu_segcblist_init(&rdp->cblist);
 	}
-	WRITE_ONCE(rdp->qlen, rdp->qlen + 1);
-	if (lazy)
-		rdp->qlen_lazy++;
-	else
+	rcu_segcblist_enqueue(&rdp->cblist, head, lazy);
+	if (!lazy)
 		rcu_idle_count_callbacks_posted();
-	smp_mb();  /* Count before adding callback for rcu_barrier(). */
-	*rdp->nxttail[RCU_NEXT_TAIL] = head;
-	rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
 
 	if (__is_kfree_rcu_offset((unsigned long)func))
 		trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
-					 rdp->qlen_lazy, rdp->qlen);
+					 rcu_segcblist_n_lazy_cbs(&rdp->cblist),
+					 rcu_segcblist_n_cbs(&rdp->cblist));
 	else
-		trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
+		trace_rcu_callback(rsp->name, head,
+				   rcu_segcblist_n_lazy_cbs(&rdp->cblist),
+				   rcu_segcblist_n_cbs(&rdp->cblist));
 
 	/* Go handle any RCU core processing required. */
 	__call_rcu_core(rsp, rdp, head, flags);
@@ -3600,7 +3475,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
 	}
 
 	/* Does this CPU have callbacks ready to invoke? */
-	if (cpu_has_callbacks_ready_to_invoke(rdp)) {
+	if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
 		rdp->n_rp_cb_ready++;
 		return 1;
 	}
@@ -3664,10 +3539,10 @@ static bool __maybe_unused rcu_cpu_has_callbacks(bool *all_lazy)
 
 	for_each_rcu_flavor(rsp) {
 		rdp = this_cpu_ptr(rsp->rda);
-		if (!rdp->nxtlist)
+		if (rcu_segcblist_empty(&rdp->cblist))
 			continue;
 		hc = true;
-		if (rdp->qlen != rdp->qlen_lazy || !all_lazy) {
+		if (rcu_segcblist_n_nonlazy_cbs(&rdp->cblist) || !all_lazy) {
 			al = false;
 			break;
 		}
@@ -3776,7 +3651,7 @@ static void _rcu_barrier(struct rcu_state *rsp)
 				__call_rcu(&rdp->barrier_head,
 					   rcu_barrier_callback, rsp, cpu, 0);
 			}
-		} else if (READ_ONCE(rdp->qlen)) {
+		} else if (rcu_segcblist_n_cbs(&rdp->cblist)) {
 			_rcu_barrier_trace(rsp, "OnlineQ", cpu,
 					   rsp->barrier_sequence);
 			smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
@@ -3885,8 +3760,9 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
 	rdp->qlen_last_fqs_check = 0;
 	rdp->n_force_qs_snap = rsp->n_force_qs;
 	rdp->blimit = blimit;
-	if (!rdp->nxtlist)
-		init_callback_list(rdp);  /* Re-enable callbacks on this CPU. */
+	if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */
+	    !init_nocb_callback_list(rdp))
+		rcu_segcblist_init(&rdp->cblist);  /* Re-enable callbacks. */
 	rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
 	rcu_sysidle_init_percpu_data(rdp->dynticks);
 	rcu_dynticks_eqs_online();
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 376c01e539c7..93889ff21dbb 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -30,6 +30,7 @@
 #include <linux/seqlock.h>
 #include <linux/swait.h>
 #include <linux/stop_machine.h>
+#include "rcu_segcblist.h"
 
 /*
  * Define shape of hierarchy based on NR_CPUS, CONFIG_RCU_FANOUT, and
@@ -335,34 +336,9 @@ struct rcu_data {
 					/* period it is aware of. */
 
 	/* 2) batch handling */
-	/*
-	 * If nxtlist is not NULL, it is partitioned as follows.
-	 * Any of the partitions might be empty, in which case the
-	 * pointer to that partition will be equal to the pointer for
-	 * the following partition.  When the list is empty, all of
-	 * the nxttail elements point to the ->nxtlist pointer itself,
-	 * which in that case is NULL.
-	 *
-	 * [nxtlist, *nxttail[RCU_DONE_TAIL]):
-	 *	Entries that batch # <= ->completed
-	 *	The grace period for these entries has completed, and
-	 *	the other grace-period-completed entries may be moved
-	 *	here temporarily in rcu_process_callbacks().
-	 * [*nxttail[RCU_DONE_TAIL], *nxttail[RCU_WAIT_TAIL]):
-	 *	Entries that batch # <= ->completed - 1: waiting for current GP
-	 * [*nxttail[RCU_WAIT_TAIL], *nxttail[RCU_NEXT_READY_TAIL]):
-	 *	Entries known to have arrived before current GP ended
-	 * [*nxttail[RCU_NEXT_READY_TAIL], *nxttail[RCU_NEXT_TAIL]):
-	 *	Entries that might have arrived after current GP ended
-	 *	Note that the value of *nxttail[RCU_NEXT_TAIL] will
-	 *	always be NULL, as this is the end of the list.
-	 */
-	struct rcu_head *nxtlist;
-	struct rcu_head **nxttail[RCU_NEXT_SIZE];
-	unsigned long	nxtcompleted[RCU_NEXT_SIZE];
-					/* grace periods for sublists. */
-	long		qlen_lazy;	/* # of lazy queued callbacks */
-	long		qlen;		/* # of queued callbacks, incl lazy */
+	struct rcu_segcblist cblist;	/* Segmented callback list, with */
+					/* different callbacks waiting for */
+					/* different grace periods. */
 	long		qlen_last_fqs_check;
 					/* qlen at last check for QS forcing */
 	unsigned long	n_cbs_invoked;	/* count of RCU cbs invoked. */
@@ -500,14 +476,11 @@ struct rcu_state {
 
 	raw_spinlock_t orphan_lock ____cacheline_internodealigned_in_smp;
 						/* Protect following fields. */
-	struct rcu_head *orphan_nxtlist;	/* Orphaned callbacks that */
+	struct rcu_cblist orphan_pend;		/* Orphaned callbacks that */
 						/*  need a grace period. */
-	struct rcu_head **orphan_nxttail;	/* Tail of above. */
-	struct rcu_head *orphan_donelist;	/* Orphaned callbacks that */
+	struct rcu_cblist orphan_done;		/* Orphaned callbacks that */
 						/*  are ready to invoke. */
-	struct rcu_head **orphan_donetail;	/* Tail of above. */
-	long qlen_lazy;				/* Number of lazy callbacks. */
-	long qlen;				/* Total number of callbacks. */
+						/* (Contains counts.) */
 	/* End of fields guarded by orphan_lock. */
 
 	struct mutex barrier_mutex;		/* Guards barrier fields. */
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 621296a6694b..f88356652dcf 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1350,10 +1350,10 @@ static bool __maybe_unused rcu_try_advance_all_cbs(void)
 		 */
 		if ((rdp->completed != rnp->completed ||
 		     unlikely(READ_ONCE(rdp->gpwrap))) &&
-		    rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
+		    rcu_segcblist_pend_cbs(&rdp->cblist))
 			note_gp_changes(rsp, rdp);
 
-		if (cpu_has_callbacks_ready_to_invoke(rdp))
+		if (rcu_segcblist_ready_cbs(&rdp->cblist))
 			cbs_ready = true;
 	}
 	return cbs_ready;
@@ -1461,7 +1461,7 @@ static void rcu_prepare_for_idle(void)
 	rdtp->last_accelerate = jiffies;
 	for_each_rcu_flavor(rsp) {
 		rdp = this_cpu_ptr(rsp->rda);
-		if (!*rdp->nxttail[RCU_DONE_TAIL])
+		if (rcu_segcblist_pend_cbs(&rdp->cblist))
 			continue;
 		rnp = rdp->mynode;
 		raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
@@ -1529,7 +1529,7 @@ static void rcu_oom_notify_cpu(void *unused)
 
 	for_each_rcu_flavor(rsp) {
 		rdp = raw_cpu_ptr(rsp->rda);
-		if (rdp->qlen_lazy != 0) {
+		if (rcu_segcblist_n_lazy_cbs(&rdp->cblist)) {
 			atomic_inc(&oom_callback_count);
 			rsp->call(&rdp->oom_head, rcu_oom_callback);
 		}
@@ -1934,30 +1934,26 @@ static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
 						     struct rcu_data *rdp,
 						     unsigned long flags)
 {
-	long ql = rsp->qlen;
-	long qll = rsp->qlen_lazy;
+	long ql = rcu_cblist_n_cbs(&rsp->orphan_done);
+	long qll = rcu_cblist_n_lazy_cbs(&rsp->orphan_done);
 
 	/* If this is not a no-CBs CPU, tell the caller to do it the old way. */
 	if (!rcu_is_nocb_cpu(smp_processor_id()))
 		return false;
-	rsp->qlen = 0;
-	rsp->qlen_lazy = 0;
 
 	/* First, enqueue the donelist, if any.  This preserves CB ordering. */
-	if (rsp->orphan_donelist != NULL) {
-		__call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
-					rsp->orphan_donetail, ql, qll, flags);
-		ql = qll = 0;
-		rsp->orphan_donelist = NULL;
-		rsp->orphan_donetail = &rsp->orphan_donelist;
+	if (!rcu_cblist_empty(&rsp->orphan_done)) {
+		__call_rcu_nocb_enqueue(rdp, rcu_cblist_head(&rsp->orphan_done),
+					rcu_cblist_tail(&rsp->orphan_done),
+					ql, qll, flags);
 	}
-	if (rsp->orphan_nxtlist != NULL) {
-		__call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
-					rsp->orphan_nxttail, ql, qll, flags);
-		ql = qll = 0;
-		rsp->orphan_nxtlist = NULL;
-		rsp->orphan_nxttail = &rsp->orphan_nxtlist;
+	if (!rcu_cblist_empty(&rsp->orphan_pend)) {
+		__call_rcu_nocb_enqueue(rdp, rcu_cblist_head(&rsp->orphan_pend),
+					rcu_cblist_tail(&rsp->orphan_pend),
+					ql, qll, flags);
 	}
+	rcu_cblist_init(&rsp->orphan_done);
+	rcu_cblist_init(&rsp->orphan_pend);
 	return true;
 }
 
@@ -2399,16 +2395,16 @@ static bool init_nocb_callback_list(struct rcu_data *rdp)
 		return false;
 
 	/* If there are early-boot callbacks, move them to nocb lists. */
-	if (rdp->nxtlist) {
-		rdp->nocb_head = rdp->nxtlist;
-		rdp->nocb_tail = rdp->nxttail[RCU_NEXT_TAIL];
-		atomic_long_set(&rdp->nocb_q_count, rdp->qlen);
-		atomic_long_set(&rdp->nocb_q_count_lazy, rdp->qlen_lazy);
-		rdp->nxtlist = NULL;
-		rdp->qlen = 0;
-		rdp->qlen_lazy = 0;
+	if (!rcu_segcblist_empty(&rdp->cblist)) {
+		rdp->nocb_head = rcu_segcblist_head(&rdp->cblist);
+		rdp->nocb_tail = rcu_segcblist_tail(&rdp->cblist);
+		atomic_long_set(&rdp->nocb_q_count,
+				rcu_segcblist_n_cbs(&rdp->cblist));
+		atomic_long_set(&rdp->nocb_q_count_lazy,
+				rcu_segcblist_n_lazy_cbs(&rdp->cblist));
+		rcu_segcblist_init(&rdp->cblist);
 	}
-	rdp->nxttail[RCU_NEXT_TAIL] = NULL;
+	rcu_segcblist_disable(&rdp->cblist);
 	return true;
 }
 
diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c
index 65b43be38e68..066c64071a7b 100644
--- a/kernel/rcu/tree_trace.c
+++ b/kernel/rcu/tree_trace.c
@@ -41,6 +41,7 @@
 #include <linux/mutex.h>
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>
+#include <linux/prefetch.h>
 
 #define RCU_TREE_NONCORE
 #include "tree.h"
@@ -128,17 +129,15 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
 		   rdp->dynticks_fqs);
 	seq_printf(m, " of=%lu", rdp->offline_fqs);
 	rcu_nocb_q_lengths(rdp, &ql, &qll);
-	qll += rdp->qlen_lazy;
-	ql += rdp->qlen;
+	qll += rcu_segcblist_n_lazy_cbs(&rdp->cblist);
+	ql += rcu_segcblist_n_cbs(&rdp->cblist);
 	seq_printf(m, " ql=%ld/%ld qs=%c%c%c%c",
 		   qll, ql,
-		   ".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
-			rdp->nxttail[RCU_NEXT_TAIL]],
-		   ".R"[rdp->nxttail[RCU_WAIT_TAIL] !=
-			rdp->nxttail[RCU_NEXT_READY_TAIL]],
-		   ".W"[rdp->nxttail[RCU_DONE_TAIL] !=
-			rdp->nxttail[RCU_WAIT_TAIL]],
-		   ".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]]);
+		   ".N"[!rcu_segcblist_segempty(&rdp->cblist, RCU_NEXT_TAIL)],
+		   ".R"[!rcu_segcblist_segempty(&rdp->cblist,
+						RCU_NEXT_READY_TAIL)],
+		   ".W"[!rcu_segcblist_segempty(&rdp->cblist, RCU_WAIT_TAIL)],
+		   ".D"[!rcu_segcblist_segempty(&rdp->cblist, RCU_DONE_TAIL)]);
 #ifdef CONFIG_RCU_BOOST
 	seq_printf(m, " kt=%d/%c ktl=%x",
 		   per_cpu(rcu_cpu_has_work, rdp->cpu),
@@ -276,7 +275,9 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
 	seq_printf(m, "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu oqlen=%ld/%ld\n",
 		   rsp->n_force_qs, rsp->n_force_qs_ngp,
 		   rsp->n_force_qs - rsp->n_force_qs_ngp,
-		   READ_ONCE(rsp->n_force_qs_lh), rsp->qlen_lazy, rsp->qlen);
+		   READ_ONCE(rsp->n_force_qs_lh),
+		   rcu_cblist_n_lazy_cbs(&rsp->orphan_done),
+		   rcu_cblist_n_cbs(&rsp->orphan_done));
 	for (rnp = &rsp->node[0]; rnp - &rsp->node[0] < rcu_num_nodes; rnp++) {
 		if (rnp->level != level) {
 			seq_puts(m, "\n");
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 14/39] srcu: Allow SRCU to access rcu_scheduler_active
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (12 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 13/39] srcu: Abstract multi-tail callback list handling Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 15/39] srcu: Allow early boot use of synchronize_srcu() Paul E. McKenney
                     ` (25 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This is primarily a code-movement commit in preparation for allowing
SRCU to handle early-boot SRCU grace periods.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcutiny.h  |  6 +++---
 kernel/rcu/tiny_plugin.h |  9 +++++----
 kernel/rcu/tree.c        |  2 +-
 kernel/rcu/tree_exp.h    | 12 -----------
 kernel/rcu/update.c      | 52 +++++++++++++++++++++++++++++++-----------------
 5 files changed, 43 insertions(+), 38 deletions(-)

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 6c9d941e3962..5219be250f00 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -217,14 +217,14 @@ static inline void exit_rcu(void)
 {
 }
 
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
+#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU)
 extern int rcu_scheduler_active __read_mostly;
 void rcu_scheduler_starting(void);
-#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+#else /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU) */
 static inline void rcu_scheduler_starting(void)
 {
 }
-#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+#endif /* #else #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU) */
 
 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE)
 
diff --git a/kernel/rcu/tiny_plugin.h b/kernel/rcu/tiny_plugin.h
index df3a60e19f07..371034e77f87 100644
--- a/kernel/rcu/tiny_plugin.h
+++ b/kernel/rcu/tiny_plugin.h
@@ -52,7 +52,7 @@ static struct rcu_ctrlblk rcu_bh_ctrlblk = {
 	RCU_TRACE(.name = "rcu_bh")
 };
 
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
+#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU)
 #include <linux/kernel_stat.h>
 
 int rcu_scheduler_active __read_mostly;
@@ -65,15 +65,16 @@ EXPORT_SYMBOL_GPL(rcu_scheduler_active);
  * to RCU_SCHEDULER_RUNNING, skipping the RCU_SCHEDULER_INIT stage.
  * The reason for this is that Tiny RCU does not need kthreads, so does
  * not have to care about the fact that the scheduler is half-initialized
- * at a certain phase of the boot process.
+ * at a certain phase of the boot process.  Unless SRCU is in the mix.
  */
 void __init rcu_scheduler_starting(void)
 {
 	WARN_ON(nr_context_switches() > 0);
-	rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
+	rcu_scheduler_active = IS_ENABLED(CONFIG_SRCU)
+		? RCU_SCHEDULER_INIT : RCU_SCHEDULER_RUNNING;
 }
 
-#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU) */
 
 #ifdef CONFIG_RCU_TRACE
 
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index ea14e6410cb8..03a1e3e09e82 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3974,7 +3974,7 @@ early_initcall(rcu_spawn_gp_kthread);
  * task is booting the system, and such primitives are no-ops).  After this
  * function is called, any synchronous grace-period primitives are run as
  * expedited, with the requesting task driving the grace period forward.
- * A later core_initcall() rcu_exp_runtime_mode() will switch to full
+ * A later core_initcall() rcu_set_runtime_mode() will switch to full
  * runtime RCU functionality.
  */
 void rcu_scheduler_starting(void)
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index a1f52bbe9db6..51ca287828a2 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -737,15 +737,3 @@ void synchronize_rcu_expedited(void)
 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
 
 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
-
-/*
- * Switch to run-time mode once Tree RCU has fully initialized.
- */
-static int __init rcu_exp_runtime_mode(void)
-{
-	rcu_test_sync_prims();
-	rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
-	rcu_test_sync_prims();
-	return 0;
-}
-core_initcall(rcu_exp_runtime_mode);
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 55c8530316c7..c5df0d756900 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -124,7 +124,7 @@ EXPORT_SYMBOL(rcu_read_lock_sched_held);
  * non-expedited counterparts?  Intended for use within RCU.  Note
  * that if the user specifies both rcu_expedited and rcu_normal, then
  * rcu_normal wins.  (Except during the time period during boot from
- * when the first task is spawned until the rcu_exp_runtime_mode()
+ * when the first task is spawned until the rcu_set_runtime_mode()
  * core_initcall() is invoked, at which point everything is expedited.)
  */
 bool rcu_gp_is_normal(void)
@@ -190,6 +190,39 @@ void rcu_end_inkernel_boot(void)
 
 #endif /* #ifndef CONFIG_TINY_RCU */
 
+/*
+ * Test each non-SRCU synchronous grace-period wait API.  This is
+ * useful just after a change in mode for these primitives, and
+ * during early boot.
+ */
+void rcu_test_sync_prims(void)
+{
+	if (!IS_ENABLED(CONFIG_PROVE_RCU))
+		return;
+	synchronize_rcu();
+	synchronize_rcu_bh();
+	synchronize_sched();
+	synchronize_rcu_expedited();
+	synchronize_rcu_bh_expedited();
+	synchronize_sched_expedited();
+}
+
+#if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU)
+
+/*
+ * Switch to run-time mode once RCU has fully initialized.
+ */
+static int __init rcu_set_runtime_mode(void)
+{
+	rcu_test_sync_prims();
+	rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
+	rcu_test_sync_prims();
+	return 0;
+}
+core_initcall(rcu_set_runtime_mode);
+
+#endif /* #if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU) */
+
 #ifdef CONFIG_PREEMPT_RCU
 
 /*
@@ -817,23 +850,6 @@ static void rcu_spawn_tasks_kthread(void)
 
 #endif /* #ifdef CONFIG_TASKS_RCU */
 
-/*
- * Test each non-SRCU synchronous grace-period wait API.  This is
- * useful just after a change in mode for these primitives, and
- * during early boot.
- */
-void rcu_test_sync_prims(void)
-{
-	if (!IS_ENABLED(CONFIG_PROVE_RCU))
-		return;
-	synchronize_rcu();
-	synchronize_rcu_bh();
-	synchronize_sched();
-	synchronize_rcu_expedited();
-	synchronize_rcu_bh_expedited();
-	synchronize_sched_expedited();
-}
-
 #ifdef CONFIG_PROVE_RCU
 
 /*
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 15/39] srcu: Allow early boot use of synchronize_srcu()
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (13 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 14/39] srcu: Allow SRCU to access rcu_scheduler_active Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 16/39] rcu: Add single-element dequeue functions to rcu_segcblist Paul E. McKenney
                     ` (24 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit checks for pre-scheduler state, and if that early in the
boot process, synchronize_srcu() and friends are no-ops.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/srcu.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 6beeba7b0b67..1026ce24922f 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -411,6 +411,8 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 			 lock_is_held(&rcu_sched_lock_map),
 			 "Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");
 
+	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
+		return;
 	might_sleep();
 	init_completion(&rcu.completion);
 
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 16/39] rcu: Add single-element dequeue functions to rcu_segcblist
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (14 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 15/39] srcu: Allow early boot use of synchronize_srcu() Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 17/39] srcu: Move rcu_seq_start() and friends to rcu.h Paul E. McKenney
                     ` (23 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit adds single-element dequeue functions to rcu_segcblist.
These are less efficient than using the extract and insert functions,
but allow more precise debugging code.  These functions are thus
expected to be used only in debug builds, for example, CONFIG_PROVE_RCU.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcu_segcblist.h | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
index 24078f3c0218..982e3e05b22a 100644
--- a/kernel/rcu/rcu_segcblist.h
+++ b/kernel/rcu/rcu_segcblist.h
@@ -290,6 +290,51 @@ static inline bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp)
 }
 
 /*
+ * Dequeue and return the first ready-to-invoke callback.  If there
+ * are no ready-to-invoke callbacks, return NULL.  Disables interrupts
+ * to avoid interference.  Does not protect from interference from other
+ * CPUs or tasks.
+ */
+static inline struct rcu_head *
+rcu_segcblist_dequeue(struct rcu_segcblist *rsclp)
+{
+	unsigned long flags;
+	int i;
+	struct rcu_head *rhp;
+
+	local_irq_save(flags);
+	if (!rcu_segcblist_ready_cbs(rsclp)) {
+		local_irq_restore(flags);
+		return NULL;
+	}
+	rhp = rsclp->head;
+	BUG_ON(!rhp);
+	rsclp->head = rhp->next;
+	for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++) {
+		if (rsclp->tails[i] != &rhp->next)
+			break;
+		rsclp->tails[i] = &rsclp->head;
+	}
+	smp_mb(); /* Dequeue before decrement for rcu_barrier(). */
+	WRITE_ONCE(rsclp->len, rsclp->len - 1);
+	local_irq_restore(flags);
+	return rhp;
+}
+
+/*
+ * Account for the fact that a previously dequeued callback turned out
+ * to be marked as lazy.
+ */
+static inline void rcu_segcblist_dequeued_lazy(struct rcu_segcblist *rsclp)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	rsclp->len_lazy--;
+	local_irq_restore(flags);
+}
+
+/*
  * Return a pointer to the first callback in the specified rcu_segcblist
  * structure.  This is useful for diagnostics.
  */
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 17/39] srcu: Move rcu_seq_start() and friends to rcu.h
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (15 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 16/39] rcu: Add single-element dequeue functions to rcu_segcblist Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 18/39] rcu: Expedited wakeups need to be fully ordered Paul E. McKenney
                     ` (22 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit moves rcu_seq_start(), rcu_seq_end(), rcu_seq_snap(),
and rcu_seq_done() from kernel/rcu/tree.c to kernel/rcu/rcu.h.
This will allow SRCU to use these functions, which in turn will
allow SRCU to move from a single global callback queue to a
per-CPU callback queue.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcu.h  | 40 ++++++++++++++++++++++++++++++++++++++++
 kernel/rcu/tree.c | 35 -----------------------------------
 2 files changed, 40 insertions(+), 35 deletions(-)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 8700a81daf56..91e0bf31f6ce 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -56,6 +56,46 @@
 #define DYNTICK_TASK_EXIT_IDLE	   (DYNTICK_TASK_NEST_VALUE + \
 				    DYNTICK_TASK_FLAG)
 
+
+/*
+ * Grace-period counter management.
+ */
+
+/* Adjust sequence number for start of update-side operation. */
+static inline void rcu_seq_start(unsigned long *sp)
+{
+	WRITE_ONCE(*sp, *sp + 1);
+	smp_mb(); /* Ensure update-side operation after counter increment. */
+	WARN_ON_ONCE(!(*sp & 0x1));
+}
+
+/* Adjust sequence number for end of update-side operation. */
+static inline void rcu_seq_end(unsigned long *sp)
+{
+	smp_mb(); /* Ensure update-side operation before counter increment. */
+	WRITE_ONCE(*sp, *sp + 1);
+	WARN_ON_ONCE(*sp & 0x1);
+}
+
+/* Take a snapshot of the update side's sequence number. */
+static inline unsigned long rcu_seq_snap(unsigned long *sp)
+{
+	unsigned long s;
+
+	s = (READ_ONCE(*sp) + 3) & ~0x1;
+	smp_mb(); /* Above access must not bleed into critical section. */
+	return s;
+}
+
+/*
+ * Given a snapshot from rcu_seq_snap(), determine whether or not a
+ * full update-side operation has occurred.
+ */
+static inline bool rcu_seq_done(unsigned long *sp, unsigned long s)
+{
+	return ULONG_CMP_GE(READ_ONCE(*sp), s);
+}
+
 /*
  * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally
  * by call_rcu() and rcu callback execution, and are therefore not part of the
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 03a1e3e09e82..a3eff40a6c17 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3409,41 +3409,6 @@ void cond_synchronize_sched(unsigned long oldstate)
 }
 EXPORT_SYMBOL_GPL(cond_synchronize_sched);
 
-/* Adjust sequence number for start of update-side operation. */
-static void rcu_seq_start(unsigned long *sp)
-{
-	WRITE_ONCE(*sp, *sp + 1);
-	smp_mb(); /* Ensure update-side operation after counter increment. */
-	WARN_ON_ONCE(!(*sp & 0x1));
-}
-
-/* Adjust sequence number for end of update-side operation. */
-static void rcu_seq_end(unsigned long *sp)
-{
-	smp_mb(); /* Ensure update-side operation before counter increment. */
-	WRITE_ONCE(*sp, *sp + 1);
-	WARN_ON_ONCE(*sp & 0x1);
-}
-
-/* Take a snapshot of the update side's sequence number. */
-static unsigned long rcu_seq_snap(unsigned long *sp)
-{
-	unsigned long s;
-
-	s = (READ_ONCE(*sp) + 3) & ~0x1;
-	smp_mb(); /* Above access must not bleed into critical section. */
-	return s;
-}
-
-/*
- * Given a snapshot from rcu_seq_snap(), determine whether or not a
- * full update-side operation has occurred.
- */
-static bool rcu_seq_done(unsigned long *sp, unsigned long s)
-{
-	return ULONG_CMP_GE(READ_ONCE(*sp), s);
-}
-
 /*
  * Check to see if there is any immediate RCU-related work to be done
  * by the current CPU, for the specified type of RCU, returning 1 if so.
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 18/39] rcu: Expedited wakeups need to be fully ordered
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (16 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 17/39] srcu: Move rcu_seq_start() and friends to rcu.h Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 19/39] rcu: Fix warning in rcu_seq_end() Paul E. McKenney
                     ` (21 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

Expedited grace periods use workqueue handlers that wake up the requesters,
but there is no lock mediating this wakeup.  Therefore, memory barriers
are required to ensure that the handler's memory references are seen by
all to occur before synchronize_*_expedited() returns to its caller.
Possibly detected by syzkaller.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree_exp.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 51ca287828a2..027e123d93c7 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -533,6 +533,7 @@ static void rcu_exp_wait_wake(struct rcu_state *rsp, unsigned long s)
 				rnp->exp_seq_rq = s;
 			spin_unlock(&rnp->exp_lock);
 		}
+		smp_mb(); /* All above changes before wakeup. */
 		wake_up_all(&rnp->exp_wq[(rsp->expedited_sequence >> 1) & 0x3]);
 	}
 	trace_rcu_exp_grace_period(rsp->name, s, TPS("endwake"));
@@ -614,6 +615,7 @@ static void _synchronize_rcu_expedited(struct rcu_state *rsp,
 	wait_event(rnp->exp_wq[(s >> 1) & 0x3],
 		   sync_exp_work_done(rsp,
 				      &rdp->exp_workdone0, s));
+	smp_mb(); /* Workqueue actions happen before return. */
 
 	/* Let the next expedited grace period start. */
 	mutex_unlock(&rsp->exp_mutex);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 19/39] rcu: Fix warning in rcu_seq_end()
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (17 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 18/39] rcu: Expedited wakeups need to be fully ordered Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 20/39] srcu: Push srcu_advance_batches() fastpath into common case Paul E. McKenney
                     ` (20 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Dmitry Vyukov, syzkaller, Paul E. McKenney

From: Dmitry Vyukov <dvyukov@google.com>

The rcu_seq_end() function increments seq signifying completion
of a grace period, after that checks that the seq is even and wakes
_synchronize_rcu_expedited().  The _synchronize_rcu_expedited() function
uses wait_event() to wait for even seq.  The problem is that wait_event()
can return as soon as seq becomes even without waiting for the wakeup.
In such case the warning in rcu_seq_end() can falsely fire if the next
expedited grace period starts before the check.

Check that seq has good value before incrementing it.

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Cc: syzkaller@googlegroups.com
Cc: linux-kernel@vger.kernel.org
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: josh@joshtriplett.org
Cc: jiangshanlai@gmail.com
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

---

syzkaller-triggered warning:

WARNING: CPU: 0 PID: 4832 at kernel/rcu/tree.c:3533
rcu_seq_end+0x110/0x140 kernel/rcu/tree.c:3533
CPU: 0 PID: 4832 Comm: kworker/0:3 Not tainted 4.10.0+ #276
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Workqueue: events wait_rcu_exp_gp
Call Trace:
 __dump_stack lib/dump_stack.c:15 [inline]
 dump_stack+0x2ee/0x3ef lib/dump_stack.c:51
 panic+0x1fb/0x412 kernel/panic.c:179
 __warn+0x1c4/0x1e0 kernel/panic.c:540
 warn_slowpath_null+0x2c/0x40 kernel/panic.c:583
 rcu_seq_end+0x110/0x140 kernel/rcu/tree.c:3533
 rcu_exp_gp_seq_end kernel/rcu/tree_exp.h:36 [inline]
 rcu_exp_wait_wake+0x8a9/0x1330 kernel/rcu/tree_exp.h:517
 rcu_exp_sel_wait_wake kernel/rcu/tree_exp.h:559 [inline]
 wait_rcu_exp_gp+0x83/0xc0 kernel/rcu/tree_exp.h:570
 process_one_work+0xc06/0x1c20 kernel/workqueue.c:2096
 worker_thread+0x223/0x19c0 kernel/workqueue.c:2230
 kthread+0x326/0x3f0 kernel/kthread.c:227
 ret_from_fork+0x31/0x40 arch/x86/entry/entry_64.S:430
---
---
 kernel/rcu/rcu.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 91e0bf31f6ce..0bc1313c49e2 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -73,8 +73,8 @@ static inline void rcu_seq_start(unsigned long *sp)
 static inline void rcu_seq_end(unsigned long *sp)
 {
 	smp_mb(); /* Ensure update-side operation before counter increment. */
+	WARN_ON_ONCE(!(*sp & 0x1));
 	WRITE_ONCE(*sp, *sp + 1);
-	WARN_ON_ONCE(*sp & 0x1);
 }
 
 /* Take a snapshot of the update side's sequence number. */
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 20/39] srcu: Push srcu_advance_batches() fastpath into common case
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (18 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 19/39] rcu: Fix warning in rcu_seq_end() Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 21/39] srcu: Move to state-based grace-period sequencing Paul E. McKenney
                     ` (19 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit simplifies the SRCU state machine by pushing the
srcu_advance_batches() idle-SRCU fastpath into the common case.  This is
done by giving srcu_reschedule() a delay parameter, which is zero in
the call from srcu_advance_batches().

This commit is a step towards numbering callbacks in order to
efficiently handle per-CPU callback lists.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/srcu.c | 27 +++++++--------------------
 1 file changed, 7 insertions(+), 20 deletions(-)

diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 1026ce24922f..febf87deaccb 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -393,8 +393,7 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 }
 EXPORT_SYMBOL_GPL(call_srcu);
 
-static void srcu_advance_batches(struct srcu_struct *sp, int trycount);
-static void srcu_reschedule(struct srcu_struct *sp);
+static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay);
 
 /*
  * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
@@ -403,7 +402,6 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 {
 	struct rcu_synchronize rcu;
 	struct rcu_head *head = &rcu.head;
-	bool done = false;
 
 	RCU_LOCKDEP_WARN(lock_is_held(&sp->dep_map) ||
 			 lock_is_held(&rcu_bh_lock_map) ||
@@ -425,25 +423,15 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 		sp->running = true;
 		rcu_batch_queue(&sp->batch_check0, head);
 		spin_unlock_irq(&sp->queue_lock);
-
-		srcu_advance_batches(sp, trycount);
-		if (!rcu_batch_empty(&sp->batch_done)) {
-			BUG_ON(sp->batch_done.head != head);
-			rcu_batch_dequeue(&sp->batch_done);
-			done = true;
-		}
 		/* give the processing owner to work_struct */
-		srcu_reschedule(sp);
+		srcu_reschedule(sp, 0);
 	} else {
 		rcu_batch_queue(&sp->batch_queue, head);
 		spin_unlock_irq(&sp->queue_lock);
 	}
 
-	if (!done) {
-		wait_for_completion(&rcu.completion);
-		smp_mb(); /* Caller's later accesses after GP. */
-	}
-
+	wait_for_completion(&rcu.completion);
+	smp_mb(); /* Caller's later accesses after GP. */
 }
 
 /**
@@ -633,7 +621,7 @@ static void srcu_invoke_callbacks(struct srcu_struct *sp)
  * Finished one round of SRCU grace period.  Start another if there are
  * more SRCU callbacks queued, otherwise put SRCU into not-running state.
  */
-static void srcu_reschedule(struct srcu_struct *sp)
+static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
 {
 	bool pending = true;
 
@@ -647,8 +635,7 @@ static void srcu_reschedule(struct srcu_struct *sp)
 	}
 
 	if (pending)
-		queue_delayed_work(system_power_efficient_wq,
-				   &sp->work, SRCU_INTERVAL);
+		queue_delayed_work(system_power_efficient_wq, &sp->work, delay);
 }
 
 /*
@@ -663,6 +650,6 @@ void process_srcu(struct work_struct *work)
 	srcu_collect_new(sp);
 	srcu_advance_batches(sp, 1);
 	srcu_invoke_callbacks(sp);
-	srcu_reschedule(sp);
+	srcu_reschedule(sp, SRCU_INTERVAL);
 }
 EXPORT_SYMBOL_GPL(process_srcu);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 21/39] srcu: Move to state-based grace-period sequencing
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (19 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 20/39] srcu: Push srcu_advance_batches() fastpath into common case Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 22/39] srcu: Add grace-period sequence numbers Paul E. McKenney
                     ` (18 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The current SRCU grace-period processing might never reach the last
portion of srcu_advance_batches().  This is OK given the current
implementation, as the first portion, up to the try_check_zero()
following the srcu_flip() is sufficient to drive grace periods forward.
However, it has the unfortunate side-effect of making it impossible to
determine when a given grace period has ended, and it will be necessary
to efficiently trace ends of grace periods in order to efficiently handle
per-CPU SRCU callback lists.

This commit therefore adds states to the SRCU grace-period processing,
so that the end of a given SRCU grace period is marked by the transition
to the SRCU_STATE_DONE state.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/srcu.h |  10 ++++-
 kernel/rcu/srcu.c    | 111 ++++++++++++++++++++++++++++-----------------------
 2 files changed, 69 insertions(+), 52 deletions(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index a598cf3ac70c..f149a685896c 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -48,7 +48,7 @@ struct srcu_struct {
 	unsigned long completed;
 	struct srcu_array __percpu *per_cpu_ref;
 	spinlock_t queue_lock; /* protect ->batch_queue, ->running */
-	bool running;
+	int srcu_state;
 	/* callbacks just queued */
 	struct rcu_batch batch_queue;
 	/* callbacks try to do the first check_zero */
@@ -62,6 +62,12 @@ struct srcu_struct {
 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 };
 
+/* Values for -> state variable. */
+#define SRCU_STATE_IDLE		0
+#define SRCU_STATE_SCAN1	1
+#define SRCU_STATE_SCAN2	2
+#define SRCU_STATE_DONE		3
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
 int __init_srcu_struct(struct srcu_struct *sp, const char *name,
@@ -89,7 +95,7 @@ void process_srcu(struct work_struct *work);
 		.completed = -300,					\
 		.per_cpu_ref = &name##_srcu_array,			\
 		.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock),	\
-		.running = false,					\
+		.srcu_state = SRCU_STATE_IDLE,				\
 		.batch_queue = RCU_BATCH_INIT(name.batch_queue),	\
 		.batch_check0 = RCU_BATCH_INIT(name.batch_check0),	\
 		.batch_check1 = RCU_BATCH_INIT(name.batch_check1),	\
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index febf87deaccb..84da09c02971 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -111,7 +111,7 @@ static int init_srcu_struct_fields(struct srcu_struct *sp)
 {
 	sp->completed = 0;
 	spin_lock_init(&sp->queue_lock);
-	sp->running = false;
+	sp->srcu_state = SRCU_STATE_IDLE;
 	rcu_batch_init(&sp->batch_queue);
 	rcu_batch_init(&sp->batch_check0);
 	rcu_batch_init(&sp->batch_check1);
@@ -264,7 +264,7 @@ void cleanup_srcu_struct(struct srcu_struct *sp)
 	if (WARN_ON(!rcu_all_batches_empty(sp)))
 		return; /* Leakage unless caller handles error. */
 	flush_delayed_work(&sp->work);
-	if (WARN_ON(sp->running))
+	if (WARN_ON(READ_ONCE(sp->srcu_state) != SRCU_STATE_IDLE))
 		return; /* Caller forgot to stop doing call_srcu()? */
 	free_percpu(sp->per_cpu_ref);
 	sp->per_cpu_ref = NULL;
@@ -385,8 +385,8 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 	spin_lock_irqsave(&sp->queue_lock, flags);
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
 	rcu_batch_queue(&sp->batch_queue, head);
-	if (!sp->running) {
-		sp->running = true;
+	if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) {
+		WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
 		queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
 	}
 	spin_unlock_irqrestore(&sp->queue_lock, flags);
@@ -418,9 +418,9 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 	head->func = wakeme_after_rcu;
 	spin_lock_irq(&sp->queue_lock);
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
-	if (!sp->running) {
+	if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) {
 		/* steal the processing owner */
-		sp->running = true;
+		WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
 		rcu_batch_queue(&sp->batch_check0, head);
 		spin_unlock_irq(&sp->queue_lock);
 		/* give the processing owner to work_struct */
@@ -542,7 +542,9 @@ static void srcu_collect_new(struct srcu_struct *sp)
  */
 static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 {
-	int idx = 1 ^ (sp->completed & 1);
+	int idx;
+
+	WARN_ON_ONCE(sp->srcu_state == SRCU_STATE_IDLE);
 
 	/*
 	 * Because readers might be delayed for an extended period after
@@ -552,48 +554,56 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 	 * invoking a callback.
 	 */
 
-	if (rcu_batch_empty(&sp->batch_check0) &&
-	    rcu_batch_empty(&sp->batch_check1))
-		return; /* no callbacks need to be advanced */
-
-	if (!try_check_zero(sp, idx, trycount))
-		return; /* failed to advance, will try after SRCU_INTERVAL */
-
-	/*
-	 * The callbacks in ->batch_check1 have already done with their
-	 * first zero check and flip back when they were enqueued on
-	 * ->batch_check0 in a previous invocation of srcu_advance_batches().
-	 * (Presumably try_check_zero() returned false during that
-	 * invocation, leaving the callbacks stranded on ->batch_check1.)
-	 * They are therefore ready to invoke, so move them to ->batch_done.
-	 */
-	rcu_batch_move(&sp->batch_done, &sp->batch_check1);
-
-	if (rcu_batch_empty(&sp->batch_check0))
-		return; /* no callbacks need to be advanced */
-	srcu_flip(sp);
-
-	/*
-	 * The callbacks in ->batch_check0 just finished their
-	 * first check zero and flip, so move them to ->batch_check1
-	 * for future checking on the other idx.
-	 */
-	rcu_batch_move(&sp->batch_check1, &sp->batch_check0);
-
-	/*
-	 * SRCU read-side critical sections are normally short, so check
-	 * at least twice in quick succession after a flip.
-	 */
-	trycount = trycount < 2 ? 2 : trycount;
-	if (!try_check_zero(sp, idx^1, trycount))
-		return; /* failed to advance, will try after SRCU_INTERVAL */
+	if (sp->srcu_state == SRCU_STATE_DONE)
+		WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
+
+	if (sp->srcu_state == SRCU_STATE_SCAN1) {
+		idx = 1 ^ (sp->completed & 1);
+		if (!try_check_zero(sp, idx, trycount))
+			return; /* readers present, retry after SRCU_INTERVAL */
+
+		/*
+		 * The callbacks in ->batch_check1 have already done
+		 * with their first zero check and flip back when they were
+		 * enqueued on ->batch_check0 in a previous invocation of
+		 * srcu_advance_batches().  (Presumably try_check_zero()
+		 * returned false during that invocation, leaving the
+		 * callbacks stranded on ->batch_check1.) They are therefore
+		 * ready to invoke, so move them to ->batch_done.
+		 */
+		rcu_batch_move(&sp->batch_done, &sp->batch_check1);
+		srcu_flip(sp);
+
+		/*
+		 * The callbacks in ->batch_check0 just finished their
+		 * first check zero and flip, so move them to ->batch_check1
+		 * for future checking on the other idx.
+		 */
+		rcu_batch_move(&sp->batch_check1, &sp->batch_check0);
+
+		WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN2);
+	}
 
-	/*
-	 * The callbacks in ->batch_check1 have now waited for all
-	 * pre-existing readers using both idx values.  They are therefore
-	 * ready to invoke, so move them to ->batch_done.
-	 */
-	rcu_batch_move(&sp->batch_done, &sp->batch_check1);
+	if (sp->srcu_state == SRCU_STATE_SCAN2) {
+
+		/*
+		 * SRCU read-side critical sections are normally short,
+		 * so check at least twice in quick succession after a flip.
+		 */
+		idx = 1 ^ (sp->completed & 1);
+		trycount = trycount < 2 ? 2 : trycount;
+		if (!try_check_zero(sp, idx, trycount))
+			return; /* readers present, retry after SRCU_INTERVAL */
+
+		/*
+		 * The callbacks in ->batch_check1 have now waited for
+		 * all pre-existing readers using both idx values.  They are
+		 * therefore ready to invoke, so move them to ->batch_done.
+		 */
+		rcu_batch_move(&sp->batch_done, &sp->batch_check1);
+
+		WRITE_ONCE(sp->srcu_state, SRCU_STATE_DONE);
+	}
 }
 
 /*
@@ -627,8 +637,9 @@ static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
 
 	if (rcu_all_batches_empty(sp)) {
 		spin_lock_irq(&sp->queue_lock);
-		if (rcu_all_batches_empty(sp)) {
-			sp->running = false;
+		if (rcu_all_batches_empty(sp) &&
+		    READ_ONCE(sp->srcu_state) == SRCU_STATE_DONE) {
+			WRITE_ONCE(sp->srcu_state, SRCU_STATE_IDLE);
 			pending = false;
 		}
 		spin_unlock_irq(&sp->queue_lock);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 22/39] srcu: Add grace-period sequence numbers
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (20 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 21/39] srcu: Move to state-based grace-period sequencing Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 23/39] srcu: Use rcu_segcblist to track SRCU callbacks Paul E. McKenney
                     ` (17 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit adds grace-period sequence numbers, which will be used to
handle mid-boot grace periods and per-CPU callback lists.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/srcu.h |  1 +
 kernel/rcu/srcu.c    | 27 +++++++++++++++++++++++----
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index f149a685896c..047ac8c28a4e 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -46,6 +46,7 @@ struct rcu_batch {
 
 struct srcu_struct {
 	unsigned long completed;
+	unsigned long srcu_gp_seq;
 	struct srcu_array __percpu *per_cpu_ref;
 	spinlock_t queue_lock; /* protect ->batch_queue, ->running */
 	int srcu_state;
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 84da09c02971..ed7c3d082b9f 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -110,6 +110,7 @@ static inline void rcu_batch_move(struct rcu_batch *to, struct rcu_batch *from)
 static int init_srcu_struct_fields(struct srcu_struct *sp)
 {
 	sp->completed = 0;
+	sp->srcu_gp_seq = 0;
 	spin_lock_init(&sp->queue_lock);
 	sp->srcu_state = SRCU_STATE_IDLE;
 	rcu_batch_init(&sp->batch_queue);
@@ -313,6 +314,15 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
 #define SYNCHRONIZE_SRCU_EXP_TRYCOUNT	12
 
 /*
+ * Start an SRCU grace period.
+ */
+static void srcu_gp_start(struct srcu_struct *sp)
+{
+	WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
+	rcu_seq_start(&sp->srcu_gp_seq);
+}
+
+/*
  * @@@ Wait until all pre-existing readers complete.  Such readers
  * will have used the index specified by "idx".
  * the caller should ensures the ->completed is not changed while checking
@@ -349,6 +359,15 @@ static void srcu_flip(struct srcu_struct *sp)
 }
 
 /*
+ * End an SRCU grace period.
+ */
+static void srcu_gp_end(struct srcu_struct *sp)
+{
+	rcu_seq_end(&sp->srcu_gp_seq);
+	WRITE_ONCE(sp->srcu_state, SRCU_STATE_DONE);
+}
+
+/*
  * Enqueue an SRCU callback on the specified srcu_struct structure,
  * initiating grace-period processing if it is not already running.
  *
@@ -386,7 +405,7 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
 	rcu_batch_queue(&sp->batch_queue, head);
 	if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) {
-		WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
+		srcu_gp_start(sp);
 		queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
 	}
 	spin_unlock_irqrestore(&sp->queue_lock, flags);
@@ -420,7 +439,7 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
 	if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) {
 		/* steal the processing owner */
-		WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
+		srcu_gp_start(sp);
 		rcu_batch_queue(&sp->batch_check0, head);
 		spin_unlock_irq(&sp->queue_lock);
 		/* give the processing owner to work_struct */
@@ -555,7 +574,7 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 	 */
 
 	if (sp->srcu_state == SRCU_STATE_DONE)
-		WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
+		srcu_gp_start(sp);
 
 	if (sp->srcu_state == SRCU_STATE_SCAN1) {
 		idx = 1 ^ (sp->completed & 1);
@@ -602,7 +621,7 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 		 */
 		rcu_batch_move(&sp->batch_done, &sp->batch_check1);
 
-		WRITE_ONCE(sp->srcu_state, SRCU_STATE_DONE);
+		srcu_gp_end(sp);
 	}
 }
 
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 23/39] srcu: Use rcu_segcblist to track SRCU callbacks
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (21 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 22/39] srcu: Add grace-period sequence numbers Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 24/39] srcu: Move combining-tree definitions for SRCU's benefit Paul E. McKenney
                     ` (16 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit switches SRCU from custom-built callback queues to the new
rcu_segcblist structure.  This change associates grace-period sequence
numbers with groups of callbacks, which will be needed for efficient
processing of per-CPU callbacks.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcu_segcblist.h | 678 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/srcu.h          |  24 +-
 kernel/rcu/rcu.h              |   6 +
 kernel/rcu/rcu_segcblist.h    | 670 -----------------------------------------
 kernel/rcu/srcu.c             | 159 ++--------
 kernel/rcu/tree.h             |   2 +-
 6 files changed, 721 insertions(+), 818 deletions(-)
 create mode 100644 include/linux/rcu_segcblist.h
 delete mode 100644 kernel/rcu/rcu_segcblist.h

diff --git a/include/linux/rcu_segcblist.h b/include/linux/rcu_segcblist.h
new file mode 100644
index 000000000000..74b1e7243955
--- /dev/null
+++ b/include/linux/rcu_segcblist.h
@@ -0,0 +1,678 @@
+/*
+ * RCU segmented callback lists
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright IBM Corporation, 2017
+ *
+ * Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ */
+
+#ifndef __KERNEL_RCU_SEGCBLIST_H
+#define __KERNEL_RCU_SEGCBLIST_H
+
+/* Simple unsegmented callback lists. */
+struct rcu_cblist {
+	struct rcu_head *head;
+	struct rcu_head **tail;
+	long len;
+	long len_lazy;
+};
+
+#define RCU_CBLIST_INITIALIZER(n) { .head = NULL, .tail = &n.head }
+
+/* Initialize simple callback list. */
+static inline void rcu_cblist_init(struct rcu_cblist *rclp)
+{
+	rclp->head = NULL;
+	rclp->tail = &rclp->head;
+	rclp->len = 0;
+	rclp->len_lazy = 0;
+}
+
+/* Is simple callback list empty? */
+static inline bool rcu_cblist_empty(struct rcu_cblist *rclp)
+{
+	return !rclp->head;
+}
+
+/* Return number of callbacks in simple callback list. */
+static inline long rcu_cblist_n_cbs(struct rcu_cblist *rclp)
+{
+	return rclp->len;
+}
+
+/* Return number of lazy callbacks in simple callback list. */
+static inline long rcu_cblist_n_lazy_cbs(struct rcu_cblist *rclp)
+{
+	return rclp->len_lazy;
+}
+
+/*
+ * Debug function to actually count the number of callbacks.
+ * If the number exceeds the limit specified, return -1.
+ */
+static inline long rcu_cblist_count_cbs(struct rcu_cblist *rclp, long lim)
+{
+	int cnt = 0;
+	struct rcu_head **rhpp = &rclp->head;
+
+	for (;;) {
+		if (!*rhpp)
+			return cnt;
+		if (++cnt > lim)
+			return -1;
+		rhpp = &(*rhpp)->next;
+	}
+}
+
+/*
+ * Dequeue the oldest rcu_head structure from the specified callback
+ * list.  This function assumes that the callback is non-lazy, but
+ * the caller can later invoke rcu_cblist_dequeued_lazy() if it
+ * finds otherwise (and if it cares about laziness).  This allows
+ * different users to have different ways of determining laziness.
+ */
+static inline struct rcu_head *rcu_cblist_dequeue(struct rcu_cblist *rclp)
+{
+	struct rcu_head *rhp;
+
+	rhp = rclp->head;
+	if (!rhp)
+		return NULL;
+	rclp->len--;
+	rclp->head = rhp->next;
+	if (!rclp->head)
+		rclp->tail = &rclp->head;
+	return rhp;
+}
+
+/*
+ * Account for the fact that a previously dequeued callback turned out
+ * to be marked as lazy.
+ */
+static inline void rcu_cblist_dequeued_lazy(struct rcu_cblist *rclp)
+{
+	rclp->len_lazy--;
+}
+
+/*
+ * Interim function to return rcu_cblist head pointer.  Longer term, the
+ * rcu_cblist will be used more pervasively, removing the need for this
+ * function.
+ */
+static inline struct rcu_head *rcu_cblist_head(struct rcu_cblist *rclp)
+{
+	return rclp->head;
+}
+
+/*
+ * Interim function to return rcu_cblist head pointer.  Longer term, the
+ * rcu_cblist will be used more pervasively, removing the need for this
+ * function.
+ */
+static inline struct rcu_head **rcu_cblist_tail(struct rcu_cblist *rclp)
+{
+	WARN_ON_ONCE(rcu_cblist_empty(rclp));
+	return rclp->tail;
+}
+
+/* Complicated segmented callback lists.  ;-) */
+
+/*
+ * Index values for segments in rcu_segcblist structure.
+ *
+ * The segments are as follows:
+ *
+ * [head, *tails[RCU_DONE_TAIL]):
+ *	Callbacks whose grace period has elapsed, and thus can be invoked.
+ * [*tails[RCU_DONE_TAIL], *tails[RCU_WAIT_TAIL]):
+ *	Callbacks waiting for the current GP from the current CPU's viewpoint.
+ * [*tails[RCU_WAIT_TAIL], *tails[RCU_NEXT_READY_TAIL]):
+ *	Callbacks that arrived before the next GP started, again from
+ *	the current CPU's viewpoint.  These can be handled by the next GP.
+ * [*tails[RCU_NEXT_READY_TAIL], *tails[RCU_NEXT_TAIL]):
+ *	Callbacks that might have arrived after the next GP started.
+ *	There is some uncertainty as to when a given GP starts and
+ *	ends, but a CPU knows the exact times if it is the one starting
+ *	or ending the GP.  Other CPUs know that the previous GP ends
+ *	before the next one starts.
+ *
+ * Note that RCU_WAIT_TAIL cannot be empty unless RCU_NEXT_READY_TAIL is also
+ * empty.
+ *
+ * The ->gp_seq[] array contains the grace-period number at which the
+ * corresponding segment of callbacks will be ready to invoke.  A given
+ * element of this array is meaningful only when the corresponding segment
+ * is non-empty, and it is never valid for RCU_DONE_TAIL (whose callbacks
+ * are already ready to invoke) or for RCU_NEXT_TAIL (whose callbacks have
+ * not yet been assigned a grace-period number).
+ */
+#define RCU_DONE_TAIL		0	/* Also RCU_WAIT head. */
+#define RCU_WAIT_TAIL		1	/* Also RCU_NEXT_READY head. */
+#define RCU_NEXT_READY_TAIL	2	/* Also RCU_NEXT head. */
+#define RCU_NEXT_TAIL		3
+#define RCU_CBLIST_NSEGS	4
+
+struct rcu_segcblist {
+	struct rcu_head *head;
+	struct rcu_head **tails[RCU_CBLIST_NSEGS];
+	unsigned long gp_seq[RCU_CBLIST_NSEGS];
+	long len;
+	long len_lazy;
+};
+
+#define RCU_SEGCBLIST_INITIALIZER(n) \
+{ \
+	.head = NULL, \
+	.tails[RCU_DONE_TAIL] = &n.head, \
+	.tails[RCU_WAIT_TAIL] = &n.head, \
+	.tails[RCU_NEXT_READY_TAIL] = &n.head, \
+	.tails[RCU_NEXT_TAIL] = &n.head, \
+}
+
+/*
+ * Initialize an rcu_segcblist structure.
+ */
+static inline void rcu_segcblist_init(struct rcu_segcblist *rsclp)
+{
+	int i;
+
+	BUILD_BUG_ON(RCU_NEXT_TAIL + 1 != ARRAY_SIZE(rsclp->gp_seq));
+	BUILD_BUG_ON(ARRAY_SIZE(rsclp->tails) != ARRAY_SIZE(rsclp->gp_seq));
+	rsclp->head = NULL;
+	for (i = 0; i < RCU_CBLIST_NSEGS; i++)
+		rsclp->tails[i] = &rsclp->head;
+	rsclp->len = 0;
+	rsclp->len_lazy = 0;
+}
+
+/*
+ * Is the specified rcu_segcblist structure empty?
+ *
+ * But careful!  The fact that the ->head field is NULL does not
+ * necessarily imply that there are no callbacks associated with
+ * this structure.  When callbacks are being invoked, they are
+ * removed as a group.  If callback invocation must be preempted,
+ * the remaining callbacks will be added back to the list.  Either
+ * way, the counts are updated later.
+ *
+ * So it is often the case that rcu_segcblist_n_cbs() should be used
+ * instead.
+ */
+static inline bool rcu_segcblist_empty(struct rcu_segcblist *rsclp)
+{
+	return !rsclp->head;
+}
+
+/* Return number of callbacks in segmented callback list. */
+static inline long rcu_segcblist_n_cbs(struct rcu_segcblist *rsclp)
+{
+	return READ_ONCE(rsclp->len);
+}
+
+/* Return number of lazy callbacks in segmented callback list. */
+static inline long rcu_segcblist_n_lazy_cbs(struct rcu_segcblist *rsclp)
+{
+	return rsclp->len_lazy;
+}
+
+/* Return number of lazy callbacks in segmented callback list. */
+static inline long rcu_segcblist_n_nonlazy_cbs(struct rcu_segcblist *rsclp)
+{
+	return rsclp->len - rsclp->len_lazy;
+}
+
+/*
+ * Is the specified rcu_segcblist enabled, for example, not corresponding
+ * to an offline or callback-offloaded CPU?
+ */
+static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp)
+{
+	return !!rsclp->tails[RCU_NEXT_TAIL];
+}
+
+/*
+ * Disable the specified rcu_segcblist structure, so that callbacks can
+ * no longer be posted to it.  This structure must be empty.
+ */
+static inline void rcu_segcblist_disable(struct rcu_segcblist *rsclp)
+{
+	WARN_ON_ONCE(!rcu_segcblist_empty(rsclp));
+	WARN_ON_ONCE(rcu_segcblist_n_cbs(rsclp));
+	WARN_ON_ONCE(rcu_segcblist_n_lazy_cbs(rsclp));
+	rsclp->tails[RCU_NEXT_TAIL] = NULL;
+}
+
+/*
+ * Is the specified segment of the specified rcu_segcblist structure
+ * empty of callbacks?
+ */
+static inline bool rcu_segcblist_segempty(struct rcu_segcblist *rsclp, int seg)
+{
+	if (seg == RCU_DONE_TAIL)
+		return &rsclp->head == rsclp->tails[RCU_DONE_TAIL];
+	return rsclp->tails[seg - 1] == rsclp->tails[seg];
+}
+
+/*
+ * Are all segments following the specified segment of the specified
+ * rcu_segcblist structure empty of callbacks?  (The specified
+ * segment might well contain callbacks.)
+ */
+static inline bool rcu_segcblist_restempty(struct rcu_segcblist *rsclp, int seg)
+{
+	return !*rsclp->tails[seg];
+}
+
+/*
+ * Does the specified rcu_segcblist structure contain callbacks that
+ * are ready to be invoked?
+ */
+static inline bool rcu_segcblist_ready_cbs(struct rcu_segcblist *rsclp)
+{
+	return rcu_segcblist_is_enabled(rsclp) &&
+	       &rsclp->head != rsclp->tails[RCU_DONE_TAIL];
+}
+
+/*
+ * Does the specified rcu_segcblist structure contain callbacks that
+ * are still pending, that is, not yet ready to be invoked?
+ */
+static inline bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp)
+{
+	return rcu_segcblist_is_enabled(rsclp) &&
+	       !rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL);
+}
+
+/*
+ * Dequeue and return the first ready-to-invoke callback.  If there
+ * are no ready-to-invoke callbacks, return NULL.  Disables interrupts
+ * to avoid interference.  Does not protect from interference from other
+ * CPUs or tasks.
+ */
+static inline struct rcu_head *
+rcu_segcblist_dequeue(struct rcu_segcblist *rsclp)
+{
+	unsigned long flags;
+	int i;
+	struct rcu_head *rhp;
+
+	local_irq_save(flags);
+	if (!rcu_segcblist_ready_cbs(rsclp)) {
+		local_irq_restore(flags);
+		return NULL;
+	}
+	rhp = rsclp->head;
+	BUG_ON(!rhp);
+	rsclp->head = rhp->next;
+	for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++) {
+		if (rsclp->tails[i] != &rhp->next)
+			break;
+		rsclp->tails[i] = &rsclp->head;
+	}
+	smp_mb(); /* Dequeue before decrement for rcu_barrier(). */
+	WRITE_ONCE(rsclp->len, rsclp->len - 1);
+	local_irq_restore(flags);
+	return rhp;
+}
+
+/*
+ * Account for the fact that a previously dequeued callback turned out
+ * to be marked as lazy.
+ */
+static inline void rcu_segcblist_dequeued_lazy(struct rcu_segcblist *rsclp)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	rsclp->len_lazy--;
+	local_irq_restore(flags);
+}
+
+/*
+ * Return a pointer to the first callback in the specified rcu_segcblist
+ * structure.  This is useful for diagnostics.
+ */
+static inline struct rcu_head *
+rcu_segcblist_first_cb(struct rcu_segcblist *rsclp)
+{
+	if (rcu_segcblist_is_enabled(rsclp))
+		return rsclp->head;
+	return NULL;
+}
+
+/*
+ * Return a pointer to the first pending callback in the specified
+ * rcu_segcblist structure.  This is useful just after posting a given
+ * callback -- if that callback is the first pending callback, then
+ * you cannot rely on someone else having already started up the required
+ * grace period.
+ */
+static inline struct rcu_head *
+rcu_segcblist_first_pend_cb(struct rcu_segcblist *rsclp)
+{
+	if (rcu_segcblist_is_enabled(rsclp))
+		return *rsclp->tails[RCU_DONE_TAIL];
+	return NULL;
+}
+
+/*
+ * Does the specified rcu_segcblist structure contain callbacks that
+ * have not yet been processed beyond having been posted, that is,
+ * does it contain callbacks in its last segment?
+ */
+static inline bool rcu_segcblist_new_cbs(struct rcu_segcblist *rsclp)
+{
+	return rcu_segcblist_is_enabled(rsclp) &&
+	       !rcu_segcblist_restempty(rsclp, RCU_NEXT_READY_TAIL);
+}
+
+/*
+ * Enqueue the specified callback onto the specified rcu_segcblist
+ * structure, updating accounting as needed.  Note that the ->len
+ * field may be accessed locklessly, hence the WRITE_ONCE().
+ * The ->len field is used by rcu_barrier() and friends to determine
+ * if it must post a callback on this structure, and it is OK
+ * for rcu_barrier() to sometimes post callbacks needlessly, but
+ * absolutely not OK for it to ever miss posting a callback.
+ */
+static inline void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
+					 struct rcu_head *rhp, bool lazy)
+{
+	WRITE_ONCE(rsclp->len, rsclp->len + 1); /* ->len sampled locklessly. */
+	if (lazy)
+		rsclp->len_lazy++;
+	smp_mb(); /* Ensure counts are updated before callback is enqueued. */
+	rhp->next = NULL;
+	*rsclp->tails[RCU_NEXT_TAIL] = rhp;
+	rsclp->tails[RCU_NEXT_TAIL] = &rhp->next;
+}
+
+/*
+ * Extract only the counts from the specified rcu_segcblist structure,
+ * and place them in the specified rcu_cblist structure.  This function
+ * supports both callback orphaning and invocation, hence the separation
+ * of counts and callbacks.  (Callbacks ready for invocation must be
+ * orphaned and adopted separately from pending callbacks, but counts
+ * apply to all callbacks.  Locking must be used to make sure that
+ * both orphaned-callbacks lists are consistent.)
+ */
+static inline void rcu_segcblist_extract_count(struct rcu_segcblist *rsclp,
+					       struct rcu_cblist *rclp)
+{
+	rclp->len_lazy += rsclp->len_lazy;
+	rclp->len += rsclp->len;
+	rsclp->len_lazy = 0;
+	WRITE_ONCE(rsclp->len, 0); /* ->len sampled locklessly. */
+}
+
+/*
+ * Extract only those callbacks ready to be invoked from the specified
+ * rcu_segcblist structure and place them in the specified rcu_cblist
+ * structure.
+ */
+static inline void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp,
+						  struct rcu_cblist *rclp)
+{
+	int i;
+
+	if (!rcu_segcblist_ready_cbs(rsclp))
+		return; /* Nothing to do. */
+	*rclp->tail = rsclp->head;
+	rsclp->head = *rsclp->tails[RCU_DONE_TAIL];
+	*rsclp->tails[RCU_DONE_TAIL] = NULL;
+	rclp->tail = rsclp->tails[RCU_DONE_TAIL];
+	for (i = RCU_CBLIST_NSEGS - 1; i >= RCU_DONE_TAIL; i--)
+		if (rsclp->tails[i] == rsclp->tails[RCU_DONE_TAIL])
+			rsclp->tails[i] = &rsclp->head;
+}
+
+/*
+ * Extract only those callbacks still pending (not yet ready to be
+ * invoked) from the specified rcu_segcblist structure and place them in
+ * the specified rcu_cblist structure.  Note that this loses information
+ * about any callbacks that might have been partway done waiting for
+ * their grace period.  Too bad!  They will have to start over.
+ */
+static inline void
+rcu_segcblist_extract_pend_cbs(struct rcu_segcblist *rsclp,
+			       struct rcu_cblist *rclp)
+{
+	int i;
+
+	if (!rcu_segcblist_pend_cbs(rsclp))
+		return; /* Nothing to do. */
+	*rclp->tail = *rsclp->tails[RCU_DONE_TAIL];
+	rclp->tail = rsclp->tails[RCU_NEXT_TAIL];
+	*rsclp->tails[RCU_DONE_TAIL] = NULL;
+	for (i = RCU_DONE_TAIL + 1; i < RCU_CBLIST_NSEGS; i++)
+		rsclp->tails[i] = rsclp->tails[RCU_DONE_TAIL];
+}
+
+/*
+ * Move the entire contents of the specified rcu_segcblist structure,
+ * counts, callbacks, and all, to the specified rcu_cblist structure.
+ * @@@ Why do we need this???  Moving early-boot CBs to NOCB lists?
+ * @@@ Memory barrier needed?  (Not if only used at boot time...)
+ */
+static inline void rcu_segcblist_extract_all(struct rcu_segcblist *rsclp,
+					     struct rcu_cblist *rclp)
+{
+	rcu_segcblist_extract_done_cbs(rsclp, rclp);
+	rcu_segcblist_extract_pend_cbs(rsclp, rclp);
+	rcu_segcblist_extract_count(rsclp, rclp);
+}
+
+/*
+ * Insert counts from the specified rcu_cblist structure in the
+ * specified rcu_segcblist structure.
+ */
+static inline void rcu_segcblist_insert_count(struct rcu_segcblist *rsclp,
+					      struct rcu_cblist *rclp)
+{
+	rsclp->len_lazy += rclp->len_lazy;
+	/* ->len sampled locklessly. */
+	WRITE_ONCE(rsclp->len, rsclp->len + rclp->len);
+	rclp->len_lazy = 0;
+	rclp->len = 0;
+}
+
+/*
+ * Move callbacks from the specified rcu_cblist to the beginning of the
+ * done-callbacks segment of the specified rcu_segcblist.
+ */
+static inline void rcu_segcblist_insert_done_cbs(struct rcu_segcblist *rsclp,
+						 struct rcu_cblist *rclp)
+{
+	int i;
+
+	if (!rclp->head)
+		return; /* No callbacks to move. */
+	*rclp->tail = rsclp->head;
+	rsclp->head = rclp->head;
+	for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++)
+		if (&rsclp->head == rsclp->tails[i])
+			rsclp->tails[i] = rclp->tail;
+		else
+			break;
+	rclp->head = NULL;
+	rclp->tail = &rclp->head;
+}
+
+/*
+ * Move callbacks from the specified rcu_cblist to the end of the
+ * new-callbacks segment of the specified rcu_segcblist.
+ */
+static inline void rcu_segcblist_insert_pend_cbs(struct rcu_segcblist *rsclp,
+						 struct rcu_cblist *rclp)
+{
+	if (!rclp->head)
+		return; /* Nothing to do. */
+	*rsclp->tails[RCU_NEXT_TAIL] = rclp->head;
+	rsclp->tails[RCU_NEXT_TAIL] = rclp->tail;
+	rclp->head = NULL;
+	rclp->tail = &rclp->head;
+}
+
+/*
+ * Advance the callbacks in the specified rcu_segcblist structure based
+ * on the current value passed in for the grace-period counter.
+ */
+static inline void rcu_segcblist_advance(struct rcu_segcblist *rsclp,
+					 unsigned long seq)
+{
+	int i, j;
+
+	WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
+	WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL));
+
+	/*
+	 * Find all callbacks whose ->gp_seq numbers indicate that they
+	 * are ready to invoke, and put them into the RCU_DONE_TAIL segment.
+	 */
+	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
+		if (ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
+			break;
+		rsclp->tails[RCU_DONE_TAIL] = rsclp->tails[i];
+	}
+
+	/* If no callbacks moved, nothing more need be done. */
+	if (i == RCU_WAIT_TAIL)
+		return;
+
+	/* Clean up tail pointers that might have been misordered above. */
+	for (j = RCU_WAIT_TAIL; j < i; j++)
+		rsclp->tails[j] = rsclp->tails[RCU_DONE_TAIL];
+
+	/*
+	 * Callbacks moved, so clean up the misordered ->tails[] pointers
+	 * that now point into the middle of the list of ready-to-invoke
+	 * callbacks.  The overall effect is to copy down the later pointers
+	 * into the gap that was created by the now-ready segments.
+	 */
+	for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
+		if (rsclp->tails[j] == rsclp->tails[RCU_NEXT_TAIL])
+			break;  /* No more callbacks. */
+		rsclp->tails[j] = rsclp->tails[i];
+		rsclp->gp_seq[j] = rsclp->gp_seq[i];
+	}
+}
+
+/*
+ * "Accelerate" callbacks based on more-accurate grace-period information.
+ * The reason for this is that RCU does not synchronize the beginnings and
+ * ends of grace periods, and that callbacks are posted locally.  This in
+ * turn means that the callbacks must be labelled conservatively early
+ * on, as getting exact information would degrade both performance and
+ * scalability.  When more accurate grace-period information becomes
+ * available, previously posted callbacks can be "accelerated", marking
+ * them to complete at the end of the earlier grace period.
+ *
+ * This function operates on an rcu_segcblist structure, and also the
+ * grace-period sequence number at which new callbacks would become
+ * ready to invoke.
+ */
+static inline bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp,
+					    unsigned long seq)
+{
+	int i;
+
+	WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
+	WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL));
+
+	/*
+	 * Find the segment preceding the oldest segment of callbacks
+	 * whose ->gp_seq[] completion is at or after that passed in via
+	 * "seq", skipping any empty segments.  This oldest segment, along
+	 * with any later segments, can be merged in with any newly arrived
+	 * callbacks in the RCU_NEXT_TAIL segment, and assigned "seq"
+	 * as their ->gp_seq[] grace-period completion sequence number.
+	 */
+	for (i = RCU_NEXT_READY_TAIL; i > RCU_DONE_TAIL; i--)
+		if (rsclp->tails[i] != rsclp->tails[i - 1] &&
+		    ULONG_CMP_LT(rsclp->gp_seq[i], seq))
+			break;
+
+	/*
+	 * If all the segments contain callbacks that correspond to
+	 * earlier grace-period sequence numbers than "seq", leave.
+	 * Assuming that the rcu_segcblist structure has enough
+	 * segments in its arrays, this can only happen if some of
+	 * the non-done segments contain callbacks that really are
+	 * ready to invoke.  This situation will get straightened
+	 * out by the next call to rcu_segcblist_advance().
+	 *
+	 * Also advance to the oldest segment of callbacks whose
+	 * ->gp_seq[] completion is at or after that passed in via "seq",
+	 * skipping any empty segments.
+	 */
+	if (++i >= RCU_NEXT_TAIL)
+		return false;
+
+	/*
+	 * Merge all later callbacks, including newly arrived callbacks,
+	 * into the segment located by the for-loop above.  Assign "seq"
+	 * as the ->gp_seq[] value in order to correctly handle the case
+	 * where there were no pending callbacks in the rcu_segcblist
+	 * structure other than in the RCU_NEXT_TAIL segment.
+	 */
+	for (; i < RCU_NEXT_TAIL; i++) {
+		rsclp->tails[i] = rsclp->tails[RCU_NEXT_TAIL];
+		rsclp->gp_seq[i] = seq;
+	}
+	return true;
+}
+
+/*
+ * Scan the specified rcu_segcblist structure for callbacks that need
+ * a grace period later than the one specified by "seq".  We don't look
+ * at the RCU_DONE_TAIL or RCU_NEXT_TAIL segments because they don't
+ * have a grace-period sequence number.
+ */
+static inline bool rcu_segcblist_future_gp_needed(struct rcu_segcblist *rsclp,
+						  unsigned long seq)
+{
+	int i;
+
+	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
+		if (rsclp->tails[i - 1] != rsclp->tails[i] &&
+		    ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
+			return true;
+	return false;
+}
+
+/*
+ * Interim function to return rcu_segcblist head pointer.  Longer term, the
+ * rcu_segcblist will be used more pervasively, removing the need for this
+ * function.
+ */
+static inline struct rcu_head *rcu_segcblist_head(struct rcu_segcblist *rsclp)
+{
+	return rsclp->head;
+}
+
+/*
+ * Interim function to return rcu_segcblist head pointer.  Longer term, the
+ * rcu_segcblist will be used more pervasively, removing the need for this
+ * function.
+ */
+static inline struct rcu_head **rcu_segcblist_tail(struct rcu_segcblist *rsclp)
+{
+	WARN_ON_ONCE(rcu_segcblist_empty(rsclp));
+	return rsclp->tails[RCU_NEXT_TAIL];
+}
+
+#endif /* __KERNEL_RCU_SEGCBLIST_H */
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 047ac8c28a4e..ad154a7bc114 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -22,7 +22,7 @@
  *	   Lai Jiangshan <laijs@cn.fujitsu.com>
  *
  * For detailed explanation of Read-Copy Update mechanism see -
- * 		Documentation/RCU/ *.txt
+ *		Documentation/RCU/ *.txt
  *
  */
 
@@ -32,31 +32,20 @@
 #include <linux/mutex.h>
 #include <linux/rcupdate.h>
 #include <linux/workqueue.h>
+#include <linux/rcu_segcblist.h>
 
 struct srcu_array {
 	unsigned long lock_count[2];
 	unsigned long unlock_count[2];
 };
 
-struct rcu_batch {
-	struct rcu_head *head, **tail;
-};
-
-#define RCU_BATCH_INIT(name) { NULL, &(name.head) }
-
 struct srcu_struct {
 	unsigned long completed;
 	unsigned long srcu_gp_seq;
 	struct srcu_array __percpu *per_cpu_ref;
-	spinlock_t queue_lock; /* protect ->batch_queue, ->running */
+	spinlock_t queue_lock; /* protect ->srcu_cblist, ->srcu_state */
 	int srcu_state;
-	/* callbacks just queued */
-	struct rcu_batch batch_queue;
-	/* callbacks try to do the first check_zero */
-	struct rcu_batch batch_check0;
-	/* callbacks done with the first check_zero and the flip */
-	struct rcu_batch batch_check1;
-	struct rcu_batch batch_done;
+	struct rcu_segcblist srcu_cblist;
 	struct delayed_work work;
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map dep_map;
@@ -97,10 +86,7 @@ void process_srcu(struct work_struct *work);
 		.per_cpu_ref = &name##_srcu_array,			\
 		.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock),	\
 		.srcu_state = SRCU_STATE_IDLE,				\
-		.batch_queue = RCU_BATCH_INIT(name.batch_queue),	\
-		.batch_check0 = RCU_BATCH_INIT(name.batch_check0),	\
-		.batch_check1 = RCU_BATCH_INIT(name.batch_check1),	\
-		.batch_done = RCU_BATCH_INIT(name.batch_done),		\
+		.srcu_cblist = RCU_SEGCBLIST_INITIALIZER(name.srcu_cblist),\
 		.work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
 		__SRCU_DEP_MAP_INIT(name)				\
 	}
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 0bc1313c49e2..a943b42a9cf7 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -87,6 +87,12 @@ static inline unsigned long rcu_seq_snap(unsigned long *sp)
 	return s;
 }
 
+/* Return the current value the update side's sequence number, no ordering. */
+static inline unsigned long rcu_seq_current(unsigned long *sp)
+{
+	return READ_ONCE(*sp);
+}
+
 /*
  * Given a snapshot from rcu_seq_snap(), determine whether or not a
  * full update-side operation has occurred.
diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
deleted file mode 100644
index 982e3e05b22a..000000000000
--- a/kernel/rcu/rcu_segcblist.h
+++ /dev/null
@@ -1,670 +0,0 @@
-/*
- * RCU segmented callback lists
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, you can access it online at
- * http://www.gnu.org/licenses/gpl-2.0.html.
- *
- * Copyright IBM Corporation, 2017
- *
- * Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
- */
-
-#ifndef __KERNEL_RCU_SEGCBLIST_H
-#define __KERNEL_RCU_SEGCBLIST_H
-
-/* Simple unsegmented callback lists. */
-struct rcu_cblist {
-	struct rcu_head *head;
-	struct rcu_head **tail;
-	long len;
-	long len_lazy;
-};
-
-#define RCU_CBLIST_INITIALIZER(n) { .head = NULL, .tail = &n.head }
-
-/* Initialize simple callback list. */
-static inline void rcu_cblist_init(struct rcu_cblist *rclp)
-{
-	rclp->head = NULL;
-	rclp->tail = &rclp->head;
-	rclp->len = 0;
-	rclp->len_lazy = 0;
-}
-
-/* Is simple callback list empty? */
-static inline bool rcu_cblist_empty(struct rcu_cblist *rclp)
-{
-	return !rclp->head;
-}
-
-/* Return number of callbacks in simple callback list. */
-static inline long rcu_cblist_n_cbs(struct rcu_cblist *rclp)
-{
-	return rclp->len;
-}
-
-/* Return number of lazy callbacks in simple callback list. */
-static inline long rcu_cblist_n_lazy_cbs(struct rcu_cblist *rclp)
-{
-	return rclp->len_lazy;
-}
-
-/*
- * Debug function to actually count the number of callbacks.
- * If the number exceeds the limit specified, return -1.
- */
-static inline long rcu_cblist_count_cbs(struct rcu_cblist *rclp, long lim)
-{
-	int cnt = 0;
-	struct rcu_head **rhpp = &rclp->head;
-
-	for (;;) {
-		if (!*rhpp)
-			return cnt;
-		if (++cnt > lim)
-			return -1;
-		rhpp = &(*rhpp)->next;
-	}
-}
-
-/*
- * Dequeue the oldest rcu_head structure from the specified callback
- * list.  This function assumes that the callback is non-lazy, but
- * the caller can later invoke rcu_cblist_dequeued_lazy() if it
- * finds otherwise (and if it cares about laziness).  This allows
- * different users to have different ways of determining laziness.
- */
-static inline struct rcu_head *rcu_cblist_dequeue(struct rcu_cblist *rclp)
-{
-	struct rcu_head *rhp;
-
-	rhp = rclp->head;
-	if (!rhp)
-		return NULL;
-	prefetch(rhp);
-	rclp->len--;
-	rclp->head = rhp->next;
-	if (!rclp->head)
-		rclp->tail = &rclp->head;
-	return rhp;
-}
-
-/*
- * Account for the fact that a previously dequeued callback turned out
- * to be marked as lazy.
- */
-static inline void rcu_cblist_dequeued_lazy(struct rcu_cblist *rclp)
-{
-	rclp->len_lazy--;
-}
-
-/*
- * Interim function to return rcu_cblist head pointer.  Longer term, the
- * rcu_cblist will be used more pervasively, removing the need for this
- * function.
- */
-static inline struct rcu_head *rcu_cblist_head(struct rcu_cblist *rclp)
-{
-	return rclp->head;
-}
-
-/*
- * Interim function to return rcu_cblist head pointer.  Longer term, the
- * rcu_cblist will be used more pervasively, removing the need for this
- * function.
- */
-static inline struct rcu_head **rcu_cblist_tail(struct rcu_cblist *rclp)
-{
-	WARN_ON_ONCE(rcu_cblist_empty(rclp));
-	return rclp->tail;
-}
-
-/* Complicated segmented callback lists.  ;-) */
-
-/*
- * Index values for segments in rcu_segcblist structure.
- *
- * The segments are as follows:
- *
- * [head, *tails[RCU_DONE_TAIL]):
- *	Callbacks whose grace period has elapsed, and thus can be invoked.
- * [*tails[RCU_DONE_TAIL], *tails[RCU_WAIT_TAIL]):
- *	Callbacks waiting for the current GP from the current CPU's viewpoint.
- * [*tails[RCU_WAIT_TAIL], *tails[RCU_NEXT_READY_TAIL]):
- *	Callbacks that arrived before the next GP started, again from
- *	the current CPU's viewpoint.  These can be handled by the next GP.
- * [*tails[RCU_NEXT_READY_TAIL], *tails[RCU_NEXT_TAIL]):
- *	Callbacks that might have arrived after the next GP started.
- *	There is some uncertainty as to when a given GP starts and
- *	ends, but a CPU knows the exact times if it is the one starting
- *	or ending the GP.  Other CPUs know that the previous GP ends
- *	before the next one starts.
- *
- * Note that RCU_WAIT_TAIL cannot be empty unless RCU_NEXT_READY_TAIL is also
- * empty.
- *
- * The ->gp_seq[] array contains the grace-period number at which the
- * corresponding segment of callbacks will be ready to invoke.  A given
- * element of this array is meaningful only when the corresponding segment
- * is non-empty, and it is never valid for RCU_DONE_TAIL (whose callbacks
- * are already ready to invoke) or for RCU_NEXT_TAIL (whose callbacks have
- * not yet been assigned a grace-period number).
- */
-#define RCU_DONE_TAIL		0	/* Also RCU_WAIT head. */
-#define RCU_WAIT_TAIL		1	/* Also RCU_NEXT_READY head. */
-#define RCU_NEXT_READY_TAIL	2	/* Also RCU_NEXT head. */
-#define RCU_NEXT_TAIL		3
-#define RCU_CBLIST_NSEGS	4
-
-struct rcu_segcblist {
-	struct rcu_head *head;
-	struct rcu_head **tails[RCU_CBLIST_NSEGS];
-	unsigned long gp_seq[RCU_CBLIST_NSEGS];
-	long len;
-	long len_lazy;
-};
-
-/*
- * Initialize an rcu_segcblist structure.
- */
-static inline void rcu_segcblist_init(struct rcu_segcblist *rsclp)
-{
-	int i;
-
-	BUILD_BUG_ON(RCU_NEXT_TAIL + 1 != ARRAY_SIZE(rsclp->gp_seq));
-	BUILD_BUG_ON(ARRAY_SIZE(rsclp->tails) != ARRAY_SIZE(rsclp->gp_seq));
-	rsclp->head = NULL;
-	for (i = 0; i < RCU_CBLIST_NSEGS; i++)
-		rsclp->tails[i] = &rsclp->head;
-	rsclp->len = 0;
-	rsclp->len_lazy = 0;
-}
-
-/*
- * Is the specified rcu_segcblist structure empty?
- *
- * But careful!  The fact that the ->head field is NULL does not
- * necessarily imply that there are no callbacks associated with
- * this structure.  When callbacks are being invoked, they are
- * removed as a group.  If callback invocation must be preempted,
- * the remaining callbacks will be added back to the list.  Either
- * way, the counts are updated later.
- *
- * So it is often the case that rcu_segcblist_n_cbs() should be used
- * instead.
- */
-static inline bool rcu_segcblist_empty(struct rcu_segcblist *rsclp)
-{
-	return !rsclp->head;
-}
-
-/* Return number of callbacks in segmented callback list. */
-static inline long rcu_segcblist_n_cbs(struct rcu_segcblist *rsclp)
-{
-	return READ_ONCE(rsclp->len);
-}
-
-/* Return number of lazy callbacks in segmented callback list. */
-static inline long rcu_segcblist_n_lazy_cbs(struct rcu_segcblist *rsclp)
-{
-	return rsclp->len_lazy;
-}
-
-/* Return number of lazy callbacks in segmented callback list. */
-static inline long rcu_segcblist_n_nonlazy_cbs(struct rcu_segcblist *rsclp)
-{
-	return rsclp->len - rsclp->len_lazy;
-}
-
-/*
- * Is the specified rcu_segcblist enabled, for example, not corresponding
- * to an offline or callback-offloaded CPU?
- */
-static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp)
-{
-	return !!rsclp->tails[RCU_NEXT_TAIL];
-}
-
-/*
- * Disable the specified rcu_segcblist structure, so that callbacks can
- * no longer be posted to it.  This structure must be empty.
- */
-static inline void rcu_segcblist_disable(struct rcu_segcblist *rsclp)
-{
-	WARN_ON_ONCE(!rcu_segcblist_empty(rsclp));
-	WARN_ON_ONCE(rcu_segcblist_n_cbs(rsclp));
-	WARN_ON_ONCE(rcu_segcblist_n_lazy_cbs(rsclp));
-	rsclp->tails[RCU_NEXT_TAIL] = NULL;
-}
-
-/*
- * Is the specified segment of the specified rcu_segcblist structure
- * empty of callbacks?
- */
-static inline bool rcu_segcblist_segempty(struct rcu_segcblist *rsclp, int seg)
-{
-	if (seg == RCU_DONE_TAIL)
-		return &rsclp->head == rsclp->tails[RCU_DONE_TAIL];
-	return rsclp->tails[seg - 1] == rsclp->tails[seg];
-}
-
-/*
- * Are all segments following the specified segment of the specified
- * rcu_segcblist structure empty of callbacks?  (The specified
- * segment might well contain callbacks.)
- */
-static inline bool rcu_segcblist_restempty(struct rcu_segcblist *rsclp, int seg)
-{
-	return !*rsclp->tails[seg];
-}
-
-/*
- * Does the specified rcu_segcblist structure contain callbacks that
- * are ready to be invoked?
- */
-static inline bool rcu_segcblist_ready_cbs(struct rcu_segcblist *rsclp)
-{
-	return rcu_segcblist_is_enabled(rsclp) &&
-	       &rsclp->head != rsclp->tails[RCU_DONE_TAIL];
-}
-
-/*
- * Does the specified rcu_segcblist structure contain callbacks that
- * are still pending, that is, not yet ready to be invoked?
- */
-static inline bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp)
-{
-	return rcu_segcblist_is_enabled(rsclp) &&
-	       !rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL);
-}
-
-/*
- * Dequeue and return the first ready-to-invoke callback.  If there
- * are no ready-to-invoke callbacks, return NULL.  Disables interrupts
- * to avoid interference.  Does not protect from interference from other
- * CPUs or tasks.
- */
-static inline struct rcu_head *
-rcu_segcblist_dequeue(struct rcu_segcblist *rsclp)
-{
-	unsigned long flags;
-	int i;
-	struct rcu_head *rhp;
-
-	local_irq_save(flags);
-	if (!rcu_segcblist_ready_cbs(rsclp)) {
-		local_irq_restore(flags);
-		return NULL;
-	}
-	rhp = rsclp->head;
-	BUG_ON(!rhp);
-	rsclp->head = rhp->next;
-	for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++) {
-		if (rsclp->tails[i] != &rhp->next)
-			break;
-		rsclp->tails[i] = &rsclp->head;
-	}
-	smp_mb(); /* Dequeue before decrement for rcu_barrier(). */
-	WRITE_ONCE(rsclp->len, rsclp->len - 1);
-	local_irq_restore(flags);
-	return rhp;
-}
-
-/*
- * Account for the fact that a previously dequeued callback turned out
- * to be marked as lazy.
- */
-static inline void rcu_segcblist_dequeued_lazy(struct rcu_segcblist *rsclp)
-{
-	unsigned long flags;
-
-	local_irq_save(flags);
-	rsclp->len_lazy--;
-	local_irq_restore(flags);
-}
-
-/*
- * Return a pointer to the first callback in the specified rcu_segcblist
- * structure.  This is useful for diagnostics.
- */
-static inline struct rcu_head *
-rcu_segcblist_first_cb(struct rcu_segcblist *rsclp)
-{
-	if (rcu_segcblist_is_enabled(rsclp))
-		return rsclp->head;
-	return NULL;
-}
-
-/*
- * Return a pointer to the first pending callback in the specified
- * rcu_segcblist structure.  This is useful just after posting a given
- * callback -- if that callback is the first pending callback, then
- * you cannot rely on someone else having already started up the required
- * grace period.
- */
-static inline struct rcu_head *
-rcu_segcblist_first_pend_cb(struct rcu_segcblist *rsclp)
-{
-	if (rcu_segcblist_is_enabled(rsclp))
-		return *rsclp->tails[RCU_DONE_TAIL];
-	return NULL;
-}
-
-/*
- * Does the specified rcu_segcblist structure contain callbacks that
- * have not yet been processed beyond having been posted, that is,
- * does it contain callbacks in its last segment?
- */
-static inline bool rcu_segcblist_new_cbs(struct rcu_segcblist *rsclp)
-{
-	return rcu_segcblist_is_enabled(rsclp) &&
-	       !rcu_segcblist_restempty(rsclp, RCU_NEXT_READY_TAIL);
-}
-
-/*
- * Enqueue the specified callback onto the specified rcu_segcblist
- * structure, updating accounting as needed.  Note that the ->len
- * field may be accessed locklessly, hence the WRITE_ONCE().
- * The ->len field is used by rcu_barrier() and friends to determine
- * if it must post a callback on this structure, and it is OK
- * for rcu_barrier() to sometimes post callbacks needlessly, but
- * absolutely not OK for it to ever miss posting a callback.
- */
-static inline void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
-					 struct rcu_head *rhp, bool lazy)
-{
-	WRITE_ONCE(rsclp->len, rsclp->len + 1); /* ->len sampled locklessly. */
-	if (lazy)
-		rsclp->len_lazy++;
-	smp_mb(); /* Ensure counts are updated before callback is enqueued. */
-	rhp->next = NULL;
-	*rsclp->tails[RCU_NEXT_TAIL] = rhp;
-	rsclp->tails[RCU_NEXT_TAIL] = &rhp->next;
-}
-
-/*
- * Extract only the counts from the specified rcu_segcblist structure,
- * and place them in the specified rcu_cblist structure.  This function
- * supports both callback orphaning and invocation, hence the separation
- * of counts and callbacks.  (Callbacks ready for invocation must be
- * orphaned and adopted separately from pending callbacks, but counts
- * apply to all callbacks.  Locking must be used to make sure that
- * both orphaned-callbacks lists are consistent.)
- */
-static inline void rcu_segcblist_extract_count(struct rcu_segcblist *rsclp,
-					       struct rcu_cblist *rclp)
-{
-	rclp->len_lazy += rsclp->len_lazy;
-	rclp->len += rsclp->len;
-	rsclp->len_lazy = 0;
-	WRITE_ONCE(rsclp->len, 0); /* ->len sampled locklessly. */
-}
-
-/*
- * Extract only those callbacks ready to be invoked from the specified
- * rcu_segcblist structure and place them in the specified rcu_cblist
- * structure.
- */
-static inline void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp,
-						  struct rcu_cblist *rclp)
-{
-	int i;
-
-	if (!rcu_segcblist_ready_cbs(rsclp))
-		return; /* Nothing to do. */
-	*rclp->tail = rsclp->head;
-	rsclp->head = *rsclp->tails[RCU_DONE_TAIL];
-	*rsclp->tails[RCU_DONE_TAIL] = NULL;
-	rclp->tail = rsclp->tails[RCU_DONE_TAIL];
-	for (i = RCU_CBLIST_NSEGS - 1; i >= RCU_DONE_TAIL; i--)
-		if (rsclp->tails[i] == rsclp->tails[RCU_DONE_TAIL])
-			rsclp->tails[i] = &rsclp->head;
-}
-
-/*
- * Extract only those callbacks still pending (not yet ready to be
- * invoked) from the specified rcu_segcblist structure and place them in
- * the specified rcu_cblist structure.  Note that this loses information
- * about any callbacks that might have been partway done waiting for
- * their grace period.  Too bad!  They will have to start over.
- */
-static inline void
-rcu_segcblist_extract_pend_cbs(struct rcu_segcblist *rsclp,
-			       struct rcu_cblist *rclp)
-{
-	int i;
-
-	if (!rcu_segcblist_pend_cbs(rsclp))
-		return; /* Nothing to do. */
-	*rclp->tail = *rsclp->tails[RCU_DONE_TAIL];
-	rclp->tail = rsclp->tails[RCU_NEXT_TAIL];
-	*rsclp->tails[RCU_DONE_TAIL] = NULL;
-	for (i = RCU_DONE_TAIL + 1; i < RCU_CBLIST_NSEGS; i++)
-		rsclp->tails[i] = rsclp->tails[RCU_DONE_TAIL];
-}
-
-/*
- * Move the entire contents of the specified rcu_segcblist structure,
- * counts, callbacks, and all, to the specified rcu_cblist structure.
- * @@@ Why do we need this???  Moving early-boot CBs to NOCB lists?
- * @@@ Memory barrier needed?  (Not if only used at boot time...)
- */
-static inline void rcu_segcblist_extract_all(struct rcu_segcblist *rsclp,
-					     struct rcu_cblist *rclp)
-{
-	rcu_segcblist_extract_done_cbs(rsclp, rclp);
-	rcu_segcblist_extract_pend_cbs(rsclp, rclp);
-	rcu_segcblist_extract_count(rsclp, rclp);
-}
-
-/*
- * Insert counts from the specified rcu_cblist structure in the
- * specified rcu_segcblist structure.
- */
-static inline void rcu_segcblist_insert_count(struct rcu_segcblist *rsclp,
-					      struct rcu_cblist *rclp)
-{
-	rsclp->len_lazy += rclp->len_lazy;
-	/* ->len sampled locklessly. */
-	WRITE_ONCE(rsclp->len, rsclp->len + rclp->len);
-	rclp->len_lazy = 0;
-	rclp->len = 0;
-}
-
-/*
- * Move callbacks from the specified rcu_cblist to the beginning of the
- * done-callbacks segment of the specified rcu_segcblist.
- */
-static inline void rcu_segcblist_insert_done_cbs(struct rcu_segcblist *rsclp,
-						 struct rcu_cblist *rclp)
-{
-	int i;
-
-	if (!rclp->head)
-		return; /* No callbacks to move. */
-	*rclp->tail = rsclp->head;
-	rsclp->head = rclp->head;
-	for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++)
-		if (&rsclp->head == rsclp->tails[i])
-			rsclp->tails[i] = rclp->tail;
-		else
-			break;
-	rclp->head = NULL;
-	rclp->tail = &rclp->head;
-}
-
-/*
- * Move callbacks from the specified rcu_cblist to the end of the
- * new-callbacks segment of the specified rcu_segcblist.
- */
-static inline void rcu_segcblist_insert_pend_cbs(struct rcu_segcblist *rsclp,
-						 struct rcu_cblist *rclp)
-{
-	if (!rclp->head)
-		return; /* Nothing to do. */
-	*rsclp->tails[RCU_NEXT_TAIL] = rclp->head;
-	rsclp->tails[RCU_NEXT_TAIL] = rclp->tail;
-	rclp->head = NULL;
-	rclp->tail = &rclp->head;
-}
-
-/*
- * Advance the callbacks in the specified rcu_segcblist structure based
- * on the current value passed in for the grace-period counter.
- */
-static inline void rcu_segcblist_advance(struct rcu_segcblist *rsclp,
-					 unsigned long seq)
-{
-	int i, j;
-
-	WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
-	WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL));
-
-	/*
-	 * Find all callbacks whose ->gp_seq numbers indicate that they
-	 * are ready to invoke, and put them into the RCU_DONE_TAIL segment.
-	 */
-	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
-		if (ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
-			break;
-		rsclp->tails[RCU_DONE_TAIL] = rsclp->tails[i];
-	}
-
-	/* If no callbacks moved, nothing more need be done. */
-	if (i == RCU_WAIT_TAIL)
-		return;
-
-	/* Clean up tail pointers that might have been misordered above. */
-	for (j = RCU_WAIT_TAIL; j < i; j++)
-		rsclp->tails[j] = rsclp->tails[RCU_DONE_TAIL];
-
-	/*
-	 * Callbacks moved, so clean up the misordered ->tails[] pointers
-	 * that now point into the middle of the list of ready-to-invoke
-	 * callbacks.  The overall effect is to copy down the later pointers
-	 * into the gap that was created by the now-ready segments.
-	 */
-	for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
-		if (rsclp->tails[j] == rsclp->tails[RCU_NEXT_TAIL])
-			break;  /* No more callbacks. */
-		rsclp->tails[j] = rsclp->tails[i];
-		rsclp->gp_seq[j] = rsclp->gp_seq[i];
-	}
-}
-
-/*
- * "Accelerate" callbacks based on more-accurate grace-period information.
- * The reason for this is that RCU does not synchronize the beginnings and
- * ends of grace periods, and that callbacks are posted locally.  This in
- * turn means that the callbacks must be labelled conservatively early
- * on, as getting exact information would degrade both performance and
- * scalability.  When more accurate grace-period information becomes
- * available, previously posted callbacks can be "accelerated", marking
- * them to complete at the end of the earlier grace period.
- *
- * This function operates on an rcu_segcblist structure, and also the
- * grace-period sequence number at which new callbacks would become
- * ready to invoke.
- */
-static inline bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp,
-					    unsigned long seq)
-{
-	int i;
-
-	WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
-	WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL));
-
-	/*
-	 * Find the segment preceding the oldest segment of callbacks
-	 * whose ->gp_seq[] completion is at or after that passed in via
-	 * "seq", skipping any empty segments.  This oldest segment, along
-	 * with any later segments, can be merged in with any newly arrived
-	 * callbacks in the RCU_NEXT_TAIL segment, and assigned "seq"
-	 * as their ->gp_seq[] grace-period completion sequence number.
-	 */
-	for (i = RCU_NEXT_READY_TAIL; i > RCU_DONE_TAIL; i--)
-		if (rsclp->tails[i] != rsclp->tails[i - 1] &&
-		    ULONG_CMP_LT(rsclp->gp_seq[i], seq))
-			break;
-
-	/*
-	 * If all the segments contain callbacks that correspond to
-	 * earlier grace-period sequence numbers than "seq", leave.
-	 * Assuming that the rcu_segcblist structure has enough
-	 * segments in its arrays, this can only happen if some of
-	 * the non-done segments contain callbacks that really are
-	 * ready to invoke.  This situation will get straightened
-	 * out by the next call to rcu_segcblist_advance().
-	 *
-	 * Also advance to the oldest segment of callbacks whose
-	 * ->gp_seq[] completion is at or after that passed in via "seq",
-	 * skipping any empty segments.
-	 */
-	if (++i >= RCU_NEXT_TAIL)
-		return false;
-
-	/*
-	 * Merge all later callbacks, including newly arrived callbacks,
-	 * into the segment located by the for-loop above.  Assign "seq"
-	 * as the ->gp_seq[] value in order to correctly handle the case
-	 * where there were no pending callbacks in the rcu_segcblist
-	 * structure other than in the RCU_NEXT_TAIL segment.
-	 */
-	for (; i < RCU_NEXT_TAIL; i++) {
-		rsclp->tails[i] = rsclp->tails[RCU_NEXT_TAIL];
-		rsclp->gp_seq[i] = seq;
-	}
-	return true;
-}
-
-/*
- * Scan the specified rcu_segcblist structure for callbacks that need
- * a grace period later than the one specified by "seq".  We don't look
- * at the RCU_DONE_TAIL or RCU_NEXT_TAIL segments because they don't
- * have a grace-period sequence number.
- */
-static inline bool rcu_segcblist_future_gp_needed(struct rcu_segcblist *rsclp,
-						  unsigned long seq)
-{
-	int i;
-
-	for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
-		if (rsclp->tails[i - 1] != rsclp->tails[i] &&
-		    ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
-			return true;
-	return false;
-}
-
-/*
- * Interim function to return rcu_segcblist head pointer.  Longer term, the
- * rcu_segcblist will be used more pervasively, removing the need for this
- * function.
- */
-static inline struct rcu_head *rcu_segcblist_head(struct rcu_segcblist *rsclp)
-{
-	return rsclp->head;
-}
-
-/*
- * Interim function to return rcu_segcblist head pointer.  Longer term, the
- * rcu_segcblist will be used more pervasively, removing the need for this
- * function.
- */
-static inline struct rcu_head **rcu_segcblist_tail(struct rcu_segcblist *rsclp)
-{
-	WARN_ON_ONCE(rcu_segcblist_empty(rsclp));
-	return rsclp->tails[RCU_NEXT_TAIL];
-}
-
-#endif /* __KERNEL_RCU_SEGCBLIST_H */
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index ed7c3d082b9f..132cd57c07f1 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -22,7 +22,7 @@
  *	   Lai Jiangshan <laijs@cn.fujitsu.com>
  *
  * For detailed explanation of Read-Copy Update mechanism see -
- * 		Documentation/RCU/ *.txt
+ *		Documentation/RCU/ *.txt
  *
  */
 
@@ -38,85 +38,13 @@
 
 #include "rcu.h"
 
-/*
- * Initialize an rcu_batch structure to empty.
- */
-static inline void rcu_batch_init(struct rcu_batch *b)
-{
-	b->head = NULL;
-	b->tail = &b->head;
-}
-
-/*
- * Enqueue a callback onto the tail of the specified rcu_batch structure.
- */
-static inline void rcu_batch_queue(struct rcu_batch *b, struct rcu_head *head)
-{
-	*b->tail = head;
-	b->tail = &head->next;
-}
-
-/*
- * Is the specified rcu_batch structure empty?
- */
-static inline bool rcu_batch_empty(struct rcu_batch *b)
-{
-	return b->tail == &b->head;
-}
-
-/*
- * Are all batches empty for the specified srcu_struct?
- */
-static inline bool rcu_all_batches_empty(struct srcu_struct *sp)
-{
-	return rcu_batch_empty(&sp->batch_done) &&
-	       rcu_batch_empty(&sp->batch_check1) &&
-	       rcu_batch_empty(&sp->batch_check0) &&
-	       rcu_batch_empty(&sp->batch_queue);
-}
-
-/*
- * Remove the callback at the head of the specified rcu_batch structure
- * and return a pointer to it, or return NULL if the structure is empty.
- */
-static inline struct rcu_head *rcu_batch_dequeue(struct rcu_batch *b)
-{
-	struct rcu_head *head;
-
-	if (rcu_batch_empty(b))
-		return NULL;
-
-	head = b->head;
-	b->head = head->next;
-	if (b->tail == &head->next)
-		rcu_batch_init(b);
-
-	return head;
-}
-
-/*
- * Move all callbacks from the rcu_batch structure specified by "from" to
- * the structure specified by "to".
- */
-static inline void rcu_batch_move(struct rcu_batch *to, struct rcu_batch *from)
-{
-	if (!rcu_batch_empty(from)) {
-		*to->tail = from->head;
-		to->tail = from->tail;
-		rcu_batch_init(from);
-	}
-}
-
 static int init_srcu_struct_fields(struct srcu_struct *sp)
 {
 	sp->completed = 0;
 	sp->srcu_gp_seq = 0;
 	spin_lock_init(&sp->queue_lock);
 	sp->srcu_state = SRCU_STATE_IDLE;
-	rcu_batch_init(&sp->batch_queue);
-	rcu_batch_init(&sp->batch_check0);
-	rcu_batch_init(&sp->batch_check1);
-	rcu_batch_init(&sp->batch_done);
+	rcu_segcblist_init(&sp->srcu_cblist);
 	INIT_DELAYED_WORK(&sp->work, process_srcu);
 	sp->per_cpu_ref = alloc_percpu(struct srcu_array);
 	return sp->per_cpu_ref ? 0 : -ENOMEM;
@@ -262,7 +190,7 @@ void cleanup_srcu_struct(struct srcu_struct *sp)
 {
 	if (WARN_ON(srcu_readers_active(sp)))
 		return; /* Leakage unless caller handles error. */
-	if (WARN_ON(!rcu_all_batches_empty(sp)))
+	if (WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist)))
 		return; /* Leakage unless caller handles error. */
 	flush_delayed_work(&sp->work);
 	if (WARN_ON(READ_ONCE(sp->srcu_state) != SRCU_STATE_IDLE))
@@ -318,6 +246,8 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
  */
 static void srcu_gp_start(struct srcu_struct *sp)
 {
+	rcu_segcblist_accelerate(&sp->srcu_cblist,
+				 rcu_seq_snap(&sp->srcu_gp_seq));
 	WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
 	rcu_seq_start(&sp->srcu_gp_seq);
 }
@@ -365,6 +295,11 @@ static void srcu_gp_end(struct srcu_struct *sp)
 {
 	rcu_seq_end(&sp->srcu_gp_seq);
 	WRITE_ONCE(sp->srcu_state, SRCU_STATE_DONE);
+
+	spin_lock_irq(&sp->queue_lock);
+	rcu_segcblist_advance(&sp->srcu_cblist,
+			      rcu_seq_current(&sp->srcu_gp_seq));
+	spin_unlock_irq(&sp->queue_lock);
 }
 
 /*
@@ -403,7 +338,7 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 	head->func = func;
 	spin_lock_irqsave(&sp->queue_lock, flags);
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
-	rcu_batch_queue(&sp->batch_queue, head);
+	rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
 	if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) {
 		srcu_gp_start(sp);
 		queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
@@ -439,13 +374,13 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
 	if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) {
 		/* steal the processing owner */
+		rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
 		srcu_gp_start(sp);
-		rcu_batch_queue(&sp->batch_check0, head);
 		spin_unlock_irq(&sp->queue_lock);
 		/* give the processing owner to work_struct */
 		srcu_reschedule(sp, 0);
 	} else {
-		rcu_batch_queue(&sp->batch_queue, head);
+		rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
 		spin_unlock_irq(&sp->queue_lock);
 	}
 
@@ -543,19 +478,6 @@ EXPORT_SYMBOL_GPL(srcu_batches_completed);
 #define SRCU_INTERVAL		1
 
 /*
- * Move any new SRCU callbacks to the first stage of the SRCU grace
- * period pipeline.
- */
-static void srcu_collect_new(struct srcu_struct *sp)
-{
-	if (!rcu_batch_empty(&sp->batch_queue)) {
-		spin_lock_irq(&sp->queue_lock);
-		rcu_batch_move(&sp->batch_check0, &sp->batch_queue);
-		spin_unlock_irq(&sp->queue_lock);
-	}
-}
-
-/*
  * Core SRCU state machine.  Advance callbacks from ->batch_check0 to
  * ->batch_check1 and then to ->batch_done as readers drain.
  */
@@ -580,26 +502,7 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 		idx = 1 ^ (sp->completed & 1);
 		if (!try_check_zero(sp, idx, trycount))
 			return; /* readers present, retry after SRCU_INTERVAL */
-
-		/*
-		 * The callbacks in ->batch_check1 have already done
-		 * with their first zero check and flip back when they were
-		 * enqueued on ->batch_check0 in a previous invocation of
-		 * srcu_advance_batches().  (Presumably try_check_zero()
-		 * returned false during that invocation, leaving the
-		 * callbacks stranded on ->batch_check1.) They are therefore
-		 * ready to invoke, so move them to ->batch_done.
-		 */
-		rcu_batch_move(&sp->batch_done, &sp->batch_check1);
 		srcu_flip(sp);
-
-		/*
-		 * The callbacks in ->batch_check0 just finished their
-		 * first check zero and flip, so move them to ->batch_check1
-		 * for future checking on the other idx.
-		 */
-		rcu_batch_move(&sp->batch_check1, &sp->batch_check0);
-
 		WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN2);
 	}
 
@@ -613,14 +516,6 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 		trycount = trycount < 2 ? 2 : trycount;
 		if (!try_check_zero(sp, idx, trycount))
 			return; /* readers present, retry after SRCU_INTERVAL */
-
-		/*
-		 * The callbacks in ->batch_check1 have now waited for
-		 * all pre-existing readers using both idx values.  They are
-		 * therefore ready to invoke, so move them to ->batch_done.
-		 */
-		rcu_batch_move(&sp->batch_done, &sp->batch_check1);
-
 		srcu_gp_end(sp);
 	}
 }
@@ -633,17 +528,26 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
  */
 static void srcu_invoke_callbacks(struct srcu_struct *sp)
 {
-	int i;
-	struct rcu_head *head;
+	struct rcu_cblist ready_cbs;
+	struct rcu_head *rhp;
 
-	for (i = 0; i < SRCU_CALLBACK_BATCH; i++) {
-		head = rcu_batch_dequeue(&sp->batch_done);
-		if (!head)
-			break;
+	spin_lock_irq(&sp->queue_lock);
+	if (!rcu_segcblist_ready_cbs(&sp->srcu_cblist)) {
+		spin_unlock_irq(&sp->queue_lock);
+		return;
+	}
+	rcu_cblist_init(&ready_cbs);
+	rcu_segcblist_extract_done_cbs(&sp->srcu_cblist, &ready_cbs);
+	spin_unlock_irq(&sp->queue_lock);
+	rhp = rcu_cblist_dequeue(&ready_cbs);
+	for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
 		local_bh_disable();
-		head->func(head);
+		rhp->func(rhp);
 		local_bh_enable();
 	}
+	spin_lock_irq(&sp->queue_lock);
+	rcu_segcblist_insert_count(&sp->srcu_cblist, &ready_cbs);
+	spin_unlock_irq(&sp->queue_lock);
 }
 
 /*
@@ -654,9 +558,9 @@ static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
 {
 	bool pending = true;
 
-	if (rcu_all_batches_empty(sp)) {
+	if (rcu_segcblist_empty(&sp->srcu_cblist)) {
 		spin_lock_irq(&sp->queue_lock);
-		if (rcu_all_batches_empty(sp) &&
+		if (rcu_segcblist_empty(&sp->srcu_cblist) &&
 		    READ_ONCE(sp->srcu_state) == SRCU_STATE_DONE) {
 			WRITE_ONCE(sp->srcu_state, SRCU_STATE_IDLE);
 			pending = false;
@@ -677,7 +581,6 @@ void process_srcu(struct work_struct *work)
 
 	sp = container_of(work, struct srcu_struct, work.work);
 
-	srcu_collect_new(sp);
 	srcu_advance_batches(sp, 1);
 	srcu_invoke_callbacks(sp);
 	srcu_reschedule(sp, SRCU_INTERVAL);
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 93889ff21dbb..4f62651588ea 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -30,7 +30,7 @@
 #include <linux/seqlock.h>
 #include <linux/swait.h>
 #include <linux/stop_machine.h>
-#include "rcu_segcblist.h"
+#include <linux/rcu_segcblist.h>
 
 /*
  * Define shape of hierarchy based on NR_CPUS, CONFIG_RCU_FANOUT, and
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 24/39] srcu: Move combining-tree definitions for SRCU's benefit
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (22 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 23/39] srcu: Use rcu_segcblist to track SRCU callbacks Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 25/39] srcu: Move rcu_init_levelspread() to rcu_tree_node.h Paul E. McKenney
                     ` (15 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit moves the C preprocessor code that defines the default shape
of the rcu_node combining tree to a new include/linux/rcu_node_tree.h
file as a first step towards enabling SRCU to create its own combining
tree, which in turn enables SRCU to implement per-CPU callback handling,
thus avoiding contention on the lock currently guarding the single list
of callbacks.  Note that users of SRCU still need to know the size of
the srcu_struct structure, hence include/linux rather than kernel/rcu.

This commit is code-movement only.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcu_node_tree.h | 102 ++++++++++++++++++++++++++++++++++++++++++
 kernel/rcu/tree.h             |  71 +----------------------------
 2 files changed, 103 insertions(+), 70 deletions(-)
 create mode 100644 include/linux/rcu_node_tree.h

diff --git a/include/linux/rcu_node_tree.h b/include/linux/rcu_node_tree.h
new file mode 100644
index 000000000000..b7eb97096b1c
--- /dev/null
+++ b/include/linux/rcu_node_tree.h
@@ -0,0 +1,102 @@
+/*
+ * RCU node combining tree definitions.  These are used to compute
+ * global attributes while avoiding common-case global contention.  A key
+ * property that these computations rely on is a tournament-style approach
+ * where only one of the tasks contending a lower level in the tree need
+ * advance to the next higher level.  If properly configured, this allows
+ * unlimited scalability while maintaining a constant level of contention
+ * on the root node.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright IBM Corporation, 2017
+ *
+ * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ */
+
+#ifndef __LINUX_RCU_NODE_TREE_H
+#define __LINUX_RCU_NODE_TREE_H
+
+/*
+ * Define shape of hierarchy based on NR_CPUS, CONFIG_RCU_FANOUT, and
+ * CONFIG_RCU_FANOUT_LEAF.
+ * In theory, it should be possible to add more levels straightforwardly.
+ * In practice, this did work well going from three levels to four.
+ * Of course, your mileage may vary.
+ */
+
+#ifdef CONFIG_RCU_FANOUT
+#define RCU_FANOUT CONFIG_RCU_FANOUT
+#else /* #ifdef CONFIG_RCU_FANOUT */
+# ifdef CONFIG_64BIT
+# define RCU_FANOUT 64
+# else
+# define RCU_FANOUT 32
+# endif
+#endif /* #else #ifdef CONFIG_RCU_FANOUT */
+
+#ifdef CONFIG_RCU_FANOUT_LEAF
+#define RCU_FANOUT_LEAF CONFIG_RCU_FANOUT_LEAF
+#else /* #ifdef CONFIG_RCU_FANOUT_LEAF */
+#define RCU_FANOUT_LEAF 16
+#endif /* #else #ifdef CONFIG_RCU_FANOUT_LEAF */
+
+#define RCU_FANOUT_1	      (RCU_FANOUT_LEAF)
+#define RCU_FANOUT_2	      (RCU_FANOUT_1 * RCU_FANOUT)
+#define RCU_FANOUT_3	      (RCU_FANOUT_2 * RCU_FANOUT)
+#define RCU_FANOUT_4	      (RCU_FANOUT_3 * RCU_FANOUT)
+
+#if NR_CPUS <= RCU_FANOUT_1
+#  define RCU_NUM_LVLS	      1
+#  define NUM_RCU_LVL_0	      1
+#  define NUM_RCU_NODES	      NUM_RCU_LVL_0
+#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0 }
+#  define RCU_NODE_NAME_INIT  { "rcu_node_0" }
+#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0" }
+#elif NR_CPUS <= RCU_FANOUT_2
+#  define RCU_NUM_LVLS	      2
+#  define NUM_RCU_LVL_0	      1
+#  define NUM_RCU_LVL_1	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
+#  define NUM_RCU_NODES	      (NUM_RCU_LVL_0 + NUM_RCU_LVL_1)
+#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0, NUM_RCU_LVL_1 }
+#  define RCU_NODE_NAME_INIT  { "rcu_node_0", "rcu_node_1" }
+#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0", "rcu_node_fqs_1" }
+#elif NR_CPUS <= RCU_FANOUT_3
+#  define RCU_NUM_LVLS	      3
+#  define NUM_RCU_LVL_0	      1
+#  define NUM_RCU_LVL_1	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
+#  define NUM_RCU_LVL_2	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
+#  define NUM_RCU_NODES	      (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2)
+#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2 }
+#  define RCU_NODE_NAME_INIT  { "rcu_node_0", "rcu_node_1", "rcu_node_2" }
+#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2" }
+#elif NR_CPUS <= RCU_FANOUT_4
+#  define RCU_NUM_LVLS	      4
+#  define NUM_RCU_LVL_0	      1
+#  define NUM_RCU_LVL_1	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_3)
+#  define NUM_RCU_LVL_2	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
+#  define NUM_RCU_LVL_3	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
+#  define NUM_RCU_NODES	      (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3)
+#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2, NUM_RCU_LVL_3 }
+#  define RCU_NODE_NAME_INIT  { "rcu_node_0", "rcu_node_1", "rcu_node_2", "rcu_node_3" }
+#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2", "rcu_node_fqs_3" }
+#else
+# error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
+#endif /* #if (NR_CPUS) <= RCU_FANOUT_1 */
+
+extern int rcu_num_lvls;
+extern int rcu_num_nodes;
+
+#endif /* __LINUX_RCU_NODE_TREE_H */
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 4f62651588ea..1bec3958d44f 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -31,76 +31,7 @@
 #include <linux/swait.h>
 #include <linux/stop_machine.h>
 #include <linux/rcu_segcblist.h>
-
-/*
- * Define shape of hierarchy based on NR_CPUS, CONFIG_RCU_FANOUT, and
- * CONFIG_RCU_FANOUT_LEAF.
- * In theory, it should be possible to add more levels straightforwardly.
- * In practice, this did work well going from three levels to four.
- * Of course, your mileage may vary.
- */
-
-#ifdef CONFIG_RCU_FANOUT
-#define RCU_FANOUT CONFIG_RCU_FANOUT
-#else /* #ifdef CONFIG_RCU_FANOUT */
-# ifdef CONFIG_64BIT
-# define RCU_FANOUT 64
-# else
-# define RCU_FANOUT 32
-# endif
-#endif /* #else #ifdef CONFIG_RCU_FANOUT */
-
-#ifdef CONFIG_RCU_FANOUT_LEAF
-#define RCU_FANOUT_LEAF CONFIG_RCU_FANOUT_LEAF
-#else /* #ifdef CONFIG_RCU_FANOUT_LEAF */
-#define RCU_FANOUT_LEAF 16
-#endif /* #else #ifdef CONFIG_RCU_FANOUT_LEAF */
-
-#define RCU_FANOUT_1	      (RCU_FANOUT_LEAF)
-#define RCU_FANOUT_2	      (RCU_FANOUT_1 * RCU_FANOUT)
-#define RCU_FANOUT_3	      (RCU_FANOUT_2 * RCU_FANOUT)
-#define RCU_FANOUT_4	      (RCU_FANOUT_3 * RCU_FANOUT)
-
-#if NR_CPUS <= RCU_FANOUT_1
-#  define RCU_NUM_LVLS	      1
-#  define NUM_RCU_LVL_0	      1
-#  define NUM_RCU_NODES	      NUM_RCU_LVL_0
-#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0 }
-#  define RCU_NODE_NAME_INIT  { "rcu_node_0" }
-#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0" }
-#elif NR_CPUS <= RCU_FANOUT_2
-#  define RCU_NUM_LVLS	      2
-#  define NUM_RCU_LVL_0	      1
-#  define NUM_RCU_LVL_1	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
-#  define NUM_RCU_NODES	      (NUM_RCU_LVL_0 + NUM_RCU_LVL_1)
-#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0, NUM_RCU_LVL_1 }
-#  define RCU_NODE_NAME_INIT  { "rcu_node_0", "rcu_node_1" }
-#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0", "rcu_node_fqs_1" }
-#elif NR_CPUS <= RCU_FANOUT_3
-#  define RCU_NUM_LVLS	      3
-#  define NUM_RCU_LVL_0	      1
-#  define NUM_RCU_LVL_1	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
-#  define NUM_RCU_LVL_2	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
-#  define NUM_RCU_NODES	      (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2)
-#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2 }
-#  define RCU_NODE_NAME_INIT  { "rcu_node_0", "rcu_node_1", "rcu_node_2" }
-#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2" }
-#elif NR_CPUS <= RCU_FANOUT_4
-#  define RCU_NUM_LVLS	      4
-#  define NUM_RCU_LVL_0	      1
-#  define NUM_RCU_LVL_1	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_3)
-#  define NUM_RCU_LVL_2	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
-#  define NUM_RCU_LVL_3	      DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
-#  define NUM_RCU_NODES	      (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3)
-#  define NUM_RCU_LVL_INIT    { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2, NUM_RCU_LVL_3 }
-#  define RCU_NODE_NAME_INIT  { "rcu_node_0", "rcu_node_1", "rcu_node_2", "rcu_node_3" }
-#  define RCU_FQS_NAME_INIT   { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2", "rcu_node_fqs_3" }
-#else
-# error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
-#endif /* #if (NR_CPUS) <= RCU_FANOUT_1 */
-
-extern int rcu_num_lvls;
-extern int rcu_num_nodes;
+#include <linux/rcu_node_tree.h>
 
 /*
  * Dynticks per-CPU state.
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 25/39] srcu: Move rcu_init_levelspread() to rcu_tree_node.h
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (23 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 24/39] srcu: Move combining-tree definitions for SRCU's benefit Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 26/39] rcu: Remove redundant levelcnt[] array from rcu_init_one() Paul E. McKenney
                     ` (14 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit moves the rcu_init_levelspread() function from
kernel/rcu/tree.c to kernel/rcu/rcu.h so that SRCU can access it.  This is
another step towards enabling SRCU to create its own combining tree.
This commit is code-movement only, give or take knock-on adjustments.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcu_node_tree.h |  3 ---
 kernel/rcu/rcu.h              | 36 ++++++++++++++++++++++++++++++++++++
 kernel/rcu/srcu.c             |  1 +
 kernel/rcu/tree.c             | 25 -------------------------
 kernel/rcu/tree_trace.c       |  1 +
 5 files changed, 38 insertions(+), 28 deletions(-)

diff --git a/include/linux/rcu_node_tree.h b/include/linux/rcu_node_tree.h
index b7eb97096b1c..4b766b61e1a0 100644
--- a/include/linux/rcu_node_tree.h
+++ b/include/linux/rcu_node_tree.h
@@ -96,7 +96,4 @@
 # error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
 #endif /* #if (NR_CPUS) <= RCU_FANOUT_1 */
 
-extern int rcu_num_lvls;
-extern int rcu_num_nodes;
-
 #endif /* __LINUX_RCU_NODE_TREE_H */
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index a943b42a9cf7..87326479b39a 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -190,4 +190,40 @@ void rcu_test_sync_prims(void);
  */
 extern void resched_cpu(int cpu);
 
+#if defined(SRCU) || !defined(TINY_RCU)
+
+#include <linux/rcu_node_tree.h>
+
+extern int rcu_num_lvls;
+extern int rcu_num_nodes;
+static bool rcu_fanout_exact;
+static int rcu_fanout_leaf;
+
+/*
+ * Compute the per-level fanout, either using the exact fanout specified
+ * or balancing the tree, depending on the rcu_fanout_exact boot parameter.
+ */
+static inline void rcu_init_levelspread(int *levelspread, const int *levelcnt)
+{
+	int i;
+
+	if (rcu_fanout_exact) {
+		levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf;
+		for (i = rcu_num_lvls - 2; i >= 0; i--)
+			levelspread[i] = RCU_FANOUT;
+	} else {
+		int ccur;
+		int cprv;
+
+		cprv = nr_cpu_ids;
+		for (i = rcu_num_lvls - 1; i >= 0; i--) {
+			ccur = levelcnt[i];
+			levelspread[i] = (cprv + ccur - 1) / ccur;
+			cprv = ccur;
+		}
+	}
+}
+
+#endif /* #if defined(SRCU) || !defined(TINY_RCU) */
+
 #endif /* __LINUX_RCU_H */
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 132cd57c07f1..d51ab050f777 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -36,6 +36,7 @@
 #include <linux/delay.h>
 #include <linux/srcu.h>
 
+#include <linux/rcu_node_tree.h>
 #include "rcu.h"
 
 static int init_srcu_struct_fields(struct srcu_struct *sp)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index a3eff40a6c17..436eaa3047e6 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3952,31 +3952,6 @@ void rcu_scheduler_starting(void)
 }
 
 /*
- * Compute the per-level fanout, either using the exact fanout specified
- * or balancing the tree, depending on the rcu_fanout_exact boot parameter.
- */
-static void __init rcu_init_levelspread(int *levelspread, const int *levelcnt)
-{
-	int i;
-
-	if (rcu_fanout_exact) {
-		levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf;
-		for (i = rcu_num_lvls - 2; i >= 0; i--)
-			levelspread[i] = RCU_FANOUT;
-	} else {
-		int ccur;
-		int cprv;
-
-		cprv = nr_cpu_ids;
-		for (i = rcu_num_lvls - 1; i >= 0; i--) {
-			ccur = levelcnt[i];
-			levelspread[i] = (cprv + ccur - 1) / ccur;
-			cprv = ccur;
-		}
-	}
-}
-
-/*
  * Helper function for rcu_init() that initializes one rcu_state structure.
  */
 static void __init rcu_init_one(struct rcu_state *rsp)
diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c
index 066c64071a7b..30c5bf89ee58 100644
--- a/kernel/rcu/tree_trace.c
+++ b/kernel/rcu/tree_trace.c
@@ -45,6 +45,7 @@
 
 #define RCU_TREE_NONCORE
 #include "tree.h"
+#include "rcu.h"
 
 static int r_open(struct inode *inode, struct file *file,
 					const struct seq_operations *op)
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 26/39] rcu: Remove redundant levelcnt[] array from rcu_init_one()
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (24 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 25/39] srcu: Move rcu_init_levelspread() to rcu_tree_node.h Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 27/39] srcu: Move rcu_node traversal macros to rcu.h Paul E. McKenney
                     ` (13 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The levelcnt[] array is identical to num_rcu_lvl[], so this commit
removes levelcnt[].

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 436eaa3047e6..21140192fd76 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3961,7 +3961,6 @@ static void __init rcu_init_one(struct rcu_state *rsp)
 	static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
 	static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
 
-	int levelcnt[RCU_NUM_LVLS];		/* # nodes in each level. */
 	int levelspread[RCU_NUM_LVLS];		/* kids/node in each level. */
 	int cpustride = 1;
 	int i;
@@ -3976,18 +3975,16 @@ static void __init rcu_init_one(struct rcu_state *rsp)
 
 	/* Initialize the level-tracking arrays. */
 
-	for (i = 0; i < rcu_num_lvls; i++)
-		levelcnt[i] = num_rcu_lvl[i];
 	for (i = 1; i < rcu_num_lvls; i++)
-		rsp->level[i] = rsp->level[i - 1] + levelcnt[i - 1];
-	rcu_init_levelspread(levelspread, levelcnt);
+		rsp->level[i] = rsp->level[i - 1] + num_rcu_lvl[i - 1];
+	rcu_init_levelspread(levelspread, num_rcu_lvl);
 
 	/* Initialize the elements themselves, starting from the leaves. */
 
 	for (i = rcu_num_lvls - 1; i >= 0; i--) {
 		cpustride *= levelspread[i];
 		rnp = rsp->level[i];
-		for (j = 0; j < levelcnt[i]; j++, rnp++) {
+		for (j = 0; j < num_rcu_lvl[i]; j++, rnp++) {
 			raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
 			lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
 						   &rcu_node_class[i], buf[i]);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 27/39] srcu: Move rcu_node traversal macros to rcu.h
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (25 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 26/39] rcu: Remove redundant levelcnt[] array from rcu_init_one() Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 28/39] srcu: Make num_rcu_lvl[] array be external Paul E. McKenney
                     ` (12 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit moves rcu_for_each_node_breadth_first(),
rcu_for_each_nonleaf_node_breadth_first(), and
rcu_for_each_leaf_node() from kernel/rcu/tree.h to
kernel/rcu/rcu.h so that SRCU can access them.
This commit is code-movement only.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcu.h  | 35 +++++++++++++++++++++++++++++++++++
 kernel/rcu/tree.h | 35 -----------------------------------
 2 files changed, 35 insertions(+), 35 deletions(-)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 87326479b39a..5c1798ec32f7 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -224,6 +224,41 @@ static inline void rcu_init_levelspread(int *levelspread, const int *levelcnt)
 	}
 }
 
+/*
+ * Do a full breadth-first scan of the rcu_node structures for the
+ * specified rcu_state structure.
+ */
+#define rcu_for_each_node_breadth_first(rsp, rnp) \
+	for ((rnp) = &(rsp)->node[0]; \
+	     (rnp) < &(rsp)->node[rcu_num_nodes]; (rnp)++)
+
+/*
+ * Do a breadth-first scan of the non-leaf rcu_node structures for the
+ * specified rcu_state structure.  Note that if there is a singleton
+ * rcu_node tree with but one rcu_node structure, this loop is a no-op.
+ */
+#define rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) \
+	for ((rnp) = &(rsp)->node[0]; \
+	     (rnp) < (rsp)->level[rcu_num_lvls - 1]; (rnp)++)
+
+/*
+ * Scan the leaves of the rcu_node hierarchy for the specified rcu_state
+ * structure.  Note that if there is a singleton rcu_node tree with but
+ * one rcu_node structure, this loop -will- visit the rcu_node structure.
+ * It is still a leaf node, even if it is also the root node.
+ */
+#define rcu_for_each_leaf_node(rsp, rnp) \
+	for ((rnp) = (rsp)->level[rcu_num_lvls - 1]; \
+	     (rnp) < &(rsp)->node[rcu_num_nodes]; (rnp)++)
+
+/*
+ * Iterate over all possible CPUs in a leaf RCU node.
+ */
+#define for_each_leaf_node_possible_cpu(rnp, cpu) \
+	for ((cpu) = cpumask_next(rnp->grplo - 1, cpu_possible_mask); \
+	     cpu <= rnp->grphi; \
+	     cpu = cpumask_next((cpu), cpu_possible_mask))
+
 #endif /* #if defined(SRCU) || !defined(TINY_RCU) */
 
 #endif /* __LINUX_RCU_H */
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 1bec3958d44f..a2a45cb629d6 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -193,41 +193,6 @@ struct rcu_node {
 #define leaf_node_cpu_bit(rnp, cpu) (1UL << ((cpu) - (rnp)->grplo))
 
 /*
- * Do a full breadth-first scan of the rcu_node structures for the
- * specified rcu_state structure.
- */
-#define rcu_for_each_node_breadth_first(rsp, rnp) \
-	for ((rnp) = &(rsp)->node[0]; \
-	     (rnp) < &(rsp)->node[rcu_num_nodes]; (rnp)++)
-
-/*
- * Do a breadth-first scan of the non-leaf rcu_node structures for the
- * specified rcu_state structure.  Note that if there is a singleton
- * rcu_node tree with but one rcu_node structure, this loop is a no-op.
- */
-#define rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) \
-	for ((rnp) = &(rsp)->node[0]; \
-	     (rnp) < (rsp)->level[rcu_num_lvls - 1]; (rnp)++)
-
-/*
- * Scan the leaves of the rcu_node hierarchy for the specified rcu_state
- * structure.  Note that if there is a singleton rcu_node tree with but
- * one rcu_node structure, this loop -will- visit the rcu_node structure.
- * It is still a leaf node, even if it is also the root node.
- */
-#define rcu_for_each_leaf_node(rsp, rnp) \
-	for ((rnp) = (rsp)->level[rcu_num_lvls - 1]; \
-	     (rnp) < &(rsp)->node[rcu_num_nodes]; (rnp)++)
-
-/*
- * Iterate over all possible CPUs in a leaf RCU node.
- */
-#define for_each_leaf_node_possible_cpu(rnp, cpu) \
-	for ((cpu) = cpumask_next(rnp->grplo - 1, cpu_possible_mask); \
-	     cpu <= rnp->grphi; \
-	     cpu = cpumask_next((cpu), cpu_possible_mask))
-
-/*
  * Union to allow "aggregate OR" operation on the need for a quiescent
  * state by the normal and expedited grace periods.
  */
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 28/39] srcu: Make num_rcu_lvl[] array be external
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (26 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 27/39] srcu: Move rcu_node traversal macros to rcu.h Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 29/39] srcu: Fix bogus try_check_zero() comment Paul E. McKenney
                     ` (11 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit makes the num_rcu_lvl[] array external so that SRCU can
make use of it for initializing its upcoming srcu_node tree.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcu.h  | 1 +
 kernel/rcu/tree.c | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 5c1798ec32f7..4303b880ac99 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -195,6 +195,7 @@ extern void resched_cpu(int cpu);
 #include <linux/rcu_node_tree.h>
 
 extern int rcu_num_lvls;
+extern int num_rcu_lvl[];
 extern int rcu_num_nodes;
 static bool rcu_fanout_exact;
 static int rcu_fanout_leaf;
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 21140192fd76..bef5765c3f68 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -123,7 +123,7 @@ static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
 module_param(rcu_fanout_leaf, int, 0444);
 int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
 /* Number of rcu_nodes at specified level. */
-static int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
+int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
 int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
 /* panic() on RCU Stall sysctl. */
 int sysctl_panic_on_rcu_stall __read_mostly;
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 29/39] srcu: Fix bogus try_check_zero() comment
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (27 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 28/39] srcu: Make num_rcu_lvl[] array be external Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 30/39] srcu: Improve rcu_seq grace-period-counter abstraction Paul E. McKenney
                     ` (10 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/srcu.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index d51ab050f777..5aeeaecfb673 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -254,10 +254,9 @@ static void srcu_gp_start(struct srcu_struct *sp)
 }
 
 /*
- * @@@ Wait until all pre-existing readers complete.  Such readers
- * will have used the index specified by "idx".
- * the caller should ensures the ->completed is not changed while checking
- * and idx = (->completed & 1) ^ 1
+ * Wait until all readers counted by array index idx complete, but loop
+ * a maximum of trycount times.  The caller must ensure that ->completed
+ * is not changed while checking.
  */
 static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
 {
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 30/39] srcu: Improve rcu_seq grace-period-counter abstraction
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (28 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 29/39] srcu: Fix bogus try_check_zero() comment Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 31/39] srcu: Allow a second bit in rcu_seq for SRCU state Paul E. McKenney
                     ` (9 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The expedited grace-period code contains several open-coded shifts
know the format of an rcu_seq grace-period counter, which is not
particularly good style.  This commit therefore creates a new
rcu_seq_ctr() function that extracts the counter portion of the
counter, and an rcu_seq_state() function that extracts the low-order
state bit.  This commit prepares for SRCU callback parallelization,
which will require two state bits.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcu.h      | 29 +++++++++++++++++++++++++----
 kernel/rcu/tree_exp.h |  9 ++++-----
 2 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 4303b880ac99..c62df93bfc1b 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -61,20 +61,41 @@
  * Grace-period counter management.
  */
 
+#define RCU_SEQ_CTR_SHIFT	1
+#define RCU_SEQ_STATE_MASK	((1 << RCU_SEQ_CTR_SHIFT) - 1)
+
+/*
+ * Return the counter portion of a sequence number previously returned
+ * by rcu_seq_snap() or rcu_seq_current().
+ */
+static inline unsigned long rcu_seq_ctr(unsigned long s)
+{
+	return s >> RCU_SEQ_CTR_SHIFT;
+}
+
+/*
+ * Return the state portion of a sequence number previously returned
+ * by rcu_seq_snap() or rcu_seq_current().
+ */
+static inline int rcu_seq_state(unsigned long s)
+{
+	return s & RCU_SEQ_STATE_MASK;
+}
+
 /* Adjust sequence number for start of update-side operation. */
 static inline void rcu_seq_start(unsigned long *sp)
 {
 	WRITE_ONCE(*sp, *sp + 1);
 	smp_mb(); /* Ensure update-side operation after counter increment. */
-	WARN_ON_ONCE(!(*sp & 0x1));
+	WARN_ON_ONCE(rcu_seq_state(*sp) != 1);
 }
 
 /* Adjust sequence number for end of update-side operation. */
 static inline void rcu_seq_end(unsigned long *sp)
 {
 	smp_mb(); /* Ensure update-side operation before counter increment. */
-	WARN_ON_ONCE(!(*sp & 0x1));
-	WRITE_ONCE(*sp, *sp + 1);
+	WARN_ON_ONCE(!rcu_seq_state(*sp));
+	WRITE_ONCE(*sp, (*sp | RCU_SEQ_STATE_MASK) + 1);
 }
 
 /* Take a snapshot of the update side's sequence number. */
@@ -82,7 +103,7 @@ static inline unsigned long rcu_seq_snap(unsigned long *sp)
 {
 	unsigned long s;
 
-	s = (READ_ONCE(*sp) + 3) & ~0x1;
+	s = (READ_ONCE(*sp) + 2 * RCU_SEQ_STATE_MASK + 1) & ~RCU_SEQ_STATE_MASK;
 	smp_mb(); /* Above access must not bleed into critical section. */
 	return s;
 }
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 027e123d93c7..e513b4ab1197 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -292,7 +292,7 @@ static bool exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
 			trace_rcu_exp_funnel_lock(rsp->name, rnp->level,
 						  rnp->grplo, rnp->grphi,
 						  TPS("wait"));
-			wait_event(rnp->exp_wq[(s >> 1) & 0x3],
+			wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
 				   sync_exp_work_done(rsp,
 						      &rdp->exp_workdone2, s));
 			return true;
@@ -534,7 +534,7 @@ static void rcu_exp_wait_wake(struct rcu_state *rsp, unsigned long s)
 			spin_unlock(&rnp->exp_lock);
 		}
 		smp_mb(); /* All above changes before wakeup. */
-		wake_up_all(&rnp->exp_wq[(rsp->expedited_sequence >> 1) & 0x3]);
+		wake_up_all(&rnp->exp_wq[rcu_seq_ctr(rsp->expedited_sequence) & 0x3]);
 	}
 	trace_rcu_exp_grace_period(rsp->name, s, TPS("endwake"));
 	mutex_unlock(&rsp->exp_wake_mutex);
@@ -612,9 +612,8 @@ static void _synchronize_rcu_expedited(struct rcu_state *rsp,
 	/* Wait for expedited grace period to complete. */
 	rdp = per_cpu_ptr(rsp->rda, raw_smp_processor_id());
 	rnp = rcu_get_root(rsp);
-	wait_event(rnp->exp_wq[(s >> 1) & 0x3],
-		   sync_exp_work_done(rsp,
-				      &rdp->exp_workdone0, s));
+	wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
+		   sync_exp_work_done(rsp, &rdp->exp_workdone0, s));
 	smp_mb(); /* Workqueue actions happen before return. */
 
 	/* Let the next expedited grace period start. */
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 31/39] srcu: Allow a second bit in rcu_seq for SRCU state
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (29 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 30/39] srcu: Improve rcu_seq grace-period-counter abstraction Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 32/39] srcu: Merge ->srcu_state into ->srcu_gp_seq Paul E. McKenney
                     ` (8 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

This commit increases the number of reserved bits at the bottom of an
rcu_seq grace-period counter from one to two, as will be needed to
accommodate SRCU's three-state grace periods.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcu.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index c62df93bfc1b..87a0ac95b551 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -61,7 +61,7 @@
  * Grace-period counter management.
  */
 
-#define RCU_SEQ_CTR_SHIFT	1
+#define RCU_SEQ_CTR_SHIFT	2
 #define RCU_SEQ_STATE_MASK	((1 << RCU_SEQ_CTR_SHIFT) - 1)
 
 /*
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 32/39] srcu: Merge ->srcu_state into ->srcu_gp_seq
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (30 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 31/39] srcu: Allow a second bit in rcu_seq for SRCU state Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 33/39] srcu: Crude control of expedited grace periods Paul E. McKenney
                     ` (7 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

Updating ->srcu_state and ->srcu_gp_seq will lead to extremely complex
race conditions given multiple callback queues, so this commit takes
advantage of the two-bit state now available in rcu_seq counters to
store the state in the bottom two bits of ->srcu_gp_seq.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/srcu.h |  5 +----
 kernel/rcu/rcu.h     | 10 ++++++++++
 kernel/rcu/srcu.c    | 55 +++++++++++++++++++++++++++++++++-------------------
 3 files changed, 46 insertions(+), 24 deletions(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index ad154a7bc114..e7dbc01b61a1 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -43,8 +43,7 @@ struct srcu_struct {
 	unsigned long completed;
 	unsigned long srcu_gp_seq;
 	struct srcu_array __percpu *per_cpu_ref;
-	spinlock_t queue_lock; /* protect ->srcu_cblist, ->srcu_state */
-	int srcu_state;
+	spinlock_t queue_lock; /* protect ->srcu_cblist */
 	struct rcu_segcblist srcu_cblist;
 	struct delayed_work work;
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
@@ -56,7 +55,6 @@ struct srcu_struct {
 #define SRCU_STATE_IDLE		0
 #define SRCU_STATE_SCAN1	1
 #define SRCU_STATE_SCAN2	2
-#define SRCU_STATE_DONE		3
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
@@ -85,7 +83,6 @@ void process_srcu(struct work_struct *work);
 		.completed = -300,					\
 		.per_cpu_ref = &name##_srcu_array,			\
 		.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock),	\
-		.srcu_state = SRCU_STATE_IDLE,				\
 		.srcu_cblist = RCU_SEGCBLIST_INITIALIZER(name.srcu_cblist),\
 		.work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
 		__SRCU_DEP_MAP_INIT(name)				\
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 87a0ac95b551..73e16ec4054b 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -82,6 +82,16 @@ static inline int rcu_seq_state(unsigned long s)
 	return s & RCU_SEQ_STATE_MASK;
 }
 
+/*
+ * Set the state portion of the pointed-to sequence number.
+ * The caller is responsible for preventing conflicting updates.
+ */
+static inline void rcu_seq_set_state(unsigned long *sp, int newstate)
+{
+	WARN_ON_ONCE(newstate & ~RCU_SEQ_STATE_MASK);
+	WRITE_ONCE(*sp, (*sp & ~RCU_SEQ_STATE_MASK) + newstate);
+}
+
 /* Adjust sequence number for start of update-side operation. */
 static inline void rcu_seq_start(unsigned long *sp)
 {
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 5aeeaecfb673..97aec5d7b316 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -44,7 +44,6 @@ static int init_srcu_struct_fields(struct srcu_struct *sp)
 	sp->completed = 0;
 	sp->srcu_gp_seq = 0;
 	spin_lock_init(&sp->queue_lock);
-	sp->srcu_state = SRCU_STATE_IDLE;
 	rcu_segcblist_init(&sp->srcu_cblist);
 	INIT_DELAYED_WORK(&sp->work, process_srcu);
 	sp->per_cpu_ref = alloc_percpu(struct srcu_array);
@@ -180,6 +179,9 @@ static bool srcu_readers_active(struct srcu_struct *sp)
 	return sum;
 }
 
+#define SRCU_CALLBACK_BATCH	10
+#define SRCU_INTERVAL		1
+
 /**
  * cleanup_srcu_struct - deconstruct a sleep-RCU structure
  * @sp: structure to clean up.
@@ -194,8 +196,10 @@ void cleanup_srcu_struct(struct srcu_struct *sp)
 	if (WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist)))
 		return; /* Leakage unless caller handles error. */
 	flush_delayed_work(&sp->work);
-	if (WARN_ON(READ_ONCE(sp->srcu_state) != SRCU_STATE_IDLE))
+	if (WARN_ON(rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) != SRCU_STATE_IDLE)) {
+		pr_info("cleanup_srcu_struct: Active srcu_struct %lu CBs %c state: %d\n", rcu_segcblist_n_cbs(&sp->srcu_cblist), ".E"[rcu_segcblist_empty(&sp->srcu_cblist)], rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)));
 		return; /* Caller forgot to stop doing call_srcu()? */
+	}
 	free_percpu(sp->per_cpu_ref);
 	sp->per_cpu_ref = NULL;
 }
@@ -247,10 +251,13 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
  */
 static void srcu_gp_start(struct srcu_struct *sp)
 {
+	int state;
+
 	rcu_segcblist_accelerate(&sp->srcu_cblist,
 				 rcu_seq_snap(&sp->srcu_gp_seq));
-	WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
 	rcu_seq_start(&sp->srcu_gp_seq);
+	state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
+	WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
 }
 
 /*
@@ -294,7 +301,6 @@ static void srcu_flip(struct srcu_struct *sp)
 static void srcu_gp_end(struct srcu_struct *sp)
 {
 	rcu_seq_end(&sp->srcu_gp_seq);
-	WRITE_ONCE(sp->srcu_state, SRCU_STATE_DONE);
 
 	spin_lock_irq(&sp->queue_lock);
 	rcu_segcblist_advance(&sp->srcu_cblist,
@@ -339,7 +345,7 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 	spin_lock_irqsave(&sp->queue_lock, flags);
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
 	rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
-	if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) {
+	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
 		srcu_gp_start(sp);
 		queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
 	}
@@ -372,7 +378,7 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 	head->func = wakeme_after_rcu;
 	spin_lock_irq(&sp->queue_lock);
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
-	if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) {
+	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
 		/* steal the processing owner */
 		rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
 		srcu_gp_start(sp);
@@ -474,9 +480,6 @@ unsigned long srcu_batches_completed(struct srcu_struct *sp)
 }
 EXPORT_SYMBOL_GPL(srcu_batches_completed);
 
-#define SRCU_CALLBACK_BATCH	10
-#define SRCU_INTERVAL		1
-
 /*
  * Core SRCU state machine.  Advance callbacks from ->batch_check0 to
  * ->batch_check1 and then to ->batch_done as readers drain.
@@ -485,28 +488,40 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 {
 	int idx;
 
-	WARN_ON_ONCE(sp->srcu_state == SRCU_STATE_IDLE);
-
 	/*
 	 * Because readers might be delayed for an extended period after
 	 * fetching ->completed for their index, at any point in time there
 	 * might well be readers using both idx=0 and idx=1.  We therefore
 	 * need to wait for readers to clear from both index values before
 	 * invoking a callback.
+	 *
+	 * The load-acquire ensures that we see the accesses performed
+	 * by the prior grace period.
 	 */
+	idx = rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq)); /* ^^^ */
+	if (idx == SRCU_STATE_IDLE) {
+		spin_lock_irq(&sp->queue_lock);
+		if (rcu_segcblist_empty(&sp->srcu_cblist)) {
+			spin_unlock_irq(&sp->queue_lock);
+			return;
+		}
+		idx = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
+		if (idx == SRCU_STATE_IDLE)
+			srcu_gp_start(sp);
+		spin_unlock_irq(&sp->queue_lock);
+		if (idx != SRCU_STATE_IDLE)
+			return; /* Someone else started the grace period. */
+	}
 
-	if (sp->srcu_state == SRCU_STATE_DONE)
-		srcu_gp_start(sp);
-
-	if (sp->srcu_state == SRCU_STATE_SCAN1) {
+	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
 		idx = 1 ^ (sp->completed & 1);
 		if (!try_check_zero(sp, idx, trycount))
 			return; /* readers present, retry after SRCU_INTERVAL */
 		srcu_flip(sp);
-		WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN2);
+		rcu_seq_set_state(&sp->srcu_gp_seq, SRCU_STATE_SCAN2);
 	}
 
-	if (sp->srcu_state == SRCU_STATE_SCAN2) {
+	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN2) {
 
 		/*
 		 * SRCU read-side critical sections are normally short,
@@ -557,14 +572,14 @@ static void srcu_invoke_callbacks(struct srcu_struct *sp)
 static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
 {
 	bool pending = true;
+	int state;
 
 	if (rcu_segcblist_empty(&sp->srcu_cblist)) {
 		spin_lock_irq(&sp->queue_lock);
+		state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
 		if (rcu_segcblist_empty(&sp->srcu_cblist) &&
-		    READ_ONCE(sp->srcu_state) == SRCU_STATE_DONE) {
-			WRITE_ONCE(sp->srcu_state, SRCU_STATE_IDLE);
+		    state == SRCU_STATE_IDLE)
 			pending = false;
-		}
 		spin_unlock_irq(&sp->queue_lock);
 	}
 
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 33/39] srcu: Crude control of expedited grace periods
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (31 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 32/39] srcu: Merge ->srcu_state into ->srcu_gp_seq Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 34/39] mm: Use static initialization for "srcu" Paul E. McKenney
                     ` (6 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

SRCU's implementation of expedited grace periods has always assumed
that the SRCU instance is idle when the expedited request arrives.
This commit improves this a bit by maintaining a count of the number
of outstanding expedited requests, thus allowing prior non-expedited
grace periods accommodate these requests by shifting to expedited mode.
However, any non-expedited wait already in progress will still wait for
the full duration.

Improved control of expedited grace periods is planned, but one step
at a time.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/srcu.h |  1 +
 kernel/rcu/srcu.c    | 84 ++++++++++++++++++++++++++++------------------------
 2 files changed, 47 insertions(+), 38 deletions(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index e7dbc01b61a1..73a1b6296224 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -42,6 +42,7 @@ struct srcu_array {
 struct srcu_struct {
 	unsigned long completed;
 	unsigned long srcu_gp_seq;
+	atomic_t srcu_exp_cnt;
 	struct srcu_array __percpu *per_cpu_ref;
 	spinlock_t queue_lock; /* protect ->srcu_cblist */
 	struct rcu_segcblist srcu_cblist;
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 97aec5d7b316..b62919be99e7 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -43,6 +43,7 @@ static int init_srcu_struct_fields(struct srcu_struct *sp)
 {
 	sp->completed = 0;
 	sp->srcu_gp_seq = 0;
+	atomic_set(&sp->srcu_exp_cnt, 0);
 	spin_lock_init(&sp->queue_lock);
 	rcu_segcblist_init(&sp->srcu_cblist);
 	INIT_DELAYED_WORK(&sp->work, process_srcu);
@@ -179,7 +180,6 @@ static bool srcu_readers_active(struct srcu_struct *sp)
 	return sum;
 }
 
-#define SRCU_CALLBACK_BATCH	10
 #define SRCU_INTERVAL		1
 
 /**
@@ -191,6 +191,7 @@ static bool srcu_readers_active(struct srcu_struct *sp)
  */
 void cleanup_srcu_struct(struct srcu_struct *sp)
 {
+	WARN_ON_ONCE(atomic_read(&sp->srcu_exp_cnt));
 	if (WARN_ON(srcu_readers_active(sp)))
 		return; /* Leakage unless caller handles error. */
 	if (WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist)))
@@ -238,13 +239,10 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
  * We use an adaptive strategy for synchronize_srcu() and especially for
  * synchronize_srcu_expedited().  We spin for a fixed time period
  * (defined below) to allow SRCU readers to exit their read-side critical
- * sections.  If there are still some readers after 10 microseconds,
- * we repeatedly block for 1-millisecond time periods.  This approach
- * has done well in testing, so there is no need for a config parameter.
+ * sections.  If there are still some readers after a few microseconds,
+ * we repeatedly block for 1-millisecond time periods.
  */
 #define SRCU_RETRY_CHECK_DELAY		5
-#define SYNCHRONIZE_SRCU_TRYCOUNT	2
-#define SYNCHRONIZE_SRCU_EXP_TRYCOUNT	12
 
 /*
  * Start an SRCU grace period.
@@ -261,16 +259,16 @@ static void srcu_gp_start(struct srcu_struct *sp)
 }
 
 /*
- * Wait until all readers counted by array index idx complete, but loop
- * a maximum of trycount times.  The caller must ensure that ->completed
- * is not changed while checking.
+ * Wait until all readers counted by array index idx complete, but
+ * loop an additional time if there is an expedited grace period pending.
+ * The caller must ensure that ->completed is not changed while checking.
  */
 static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
 {
 	for (;;) {
 		if (srcu_readers_active_idx_check(sp, idx))
 			return true;
-		if (--trycount <= 0)
+		if (--trycount + !!atomic_read(&sp->srcu_exp_cnt) <= 0)
 			return false;
 		udelay(SRCU_RETRY_CHECK_DELAY);
 	}
@@ -358,7 +356,7 @@ static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay);
 /*
  * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
  */
-static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
+static void __synchronize_srcu(struct srcu_struct *sp)
 {
 	struct rcu_synchronize rcu;
 	struct rcu_head *head = &rcu.head;
@@ -395,6 +393,32 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 }
 
 /**
+ * synchronize_srcu_expedited - Brute-force SRCU grace period
+ * @sp: srcu_struct with which to synchronize.
+ *
+ * Wait for an SRCU grace period to elapse, but be more aggressive about
+ * spinning rather than blocking when waiting.
+ *
+ * Note that synchronize_srcu_expedited() has the same deadlock and
+ * memory-ordering properties as does synchronize_srcu().
+ */
+void synchronize_srcu_expedited(struct srcu_struct *sp)
+{
+	bool do_norm = rcu_gp_is_normal();
+
+	if (!do_norm) {
+		atomic_inc(&sp->srcu_exp_cnt);
+		smp_mb__after_atomic(); /* increment before GP. */
+	}
+	__synchronize_srcu(sp);
+	if (!do_norm) {
+		smp_mb__before_atomic(); /* GP before decrement. */
+		atomic_dec(&sp->srcu_exp_cnt);
+	}
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
+
+/**
  * synchronize_srcu - wait for prior SRCU read-side critical-section completion
  * @sp: srcu_struct with which to synchronize.
  *
@@ -435,29 +459,14 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
  */
 void synchronize_srcu(struct srcu_struct *sp)
 {
-	__synchronize_srcu(sp, (rcu_gp_is_expedited() && !rcu_gp_is_normal())
-			   ? SYNCHRONIZE_SRCU_EXP_TRYCOUNT
-			   : SYNCHRONIZE_SRCU_TRYCOUNT);
+	if (rcu_gp_is_expedited())
+		synchronize_srcu_expedited(sp);
+	else
+		__synchronize_srcu(sp);
 }
 EXPORT_SYMBOL_GPL(synchronize_srcu);
 
 /**
- * synchronize_srcu_expedited - Brute-force SRCU grace period
- * @sp: srcu_struct with which to synchronize.
- *
- * Wait for an SRCU grace period to elapse, but be more aggressive about
- * spinning rather than blocking when waiting.
- *
- * Note that synchronize_srcu_expedited() has the same deadlock and
- * memory-ordering properties as does synchronize_srcu().
- */
-void synchronize_srcu_expedited(struct srcu_struct *sp)
-{
-	__synchronize_srcu(sp, SYNCHRONIZE_SRCU_EXP_TRYCOUNT);
-}
-EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
-
-/**
  * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
  * @sp: srcu_struct on which to wait for in-flight callbacks.
  */
@@ -484,7 +493,7 @@ EXPORT_SYMBOL_GPL(srcu_batches_completed);
  * Core SRCU state machine.  Advance callbacks from ->batch_check0 to
  * ->batch_check1 and then to ->batch_done as readers drain.
  */
-static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
+static void srcu_advance_batches(struct srcu_struct *sp)
 {
 	int idx;
 
@@ -515,8 +524,8 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 
 	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
 		idx = 1 ^ (sp->completed & 1);
-		if (!try_check_zero(sp, idx, trycount))
-			return; /* readers present, retry after SRCU_INTERVAL */
+		if (!try_check_zero(sp, idx, 1))
+			return; /* readers present, retry later. */
 		srcu_flip(sp);
 		rcu_seq_set_state(&sp->srcu_gp_seq, SRCU_STATE_SCAN2);
 	}
@@ -528,9 +537,8 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 		 * so check at least twice in quick succession after a flip.
 		 */
 		idx = 1 ^ (sp->completed & 1);
-		trycount = trycount < 2 ? 2 : trycount;
-		if (!try_check_zero(sp, idx, trycount))
-			return; /* readers present, retry after SRCU_INTERVAL */
+		if (!try_check_zero(sp, idx, 2))
+			return; /* readers present, retry after later. */
 		srcu_gp_end(sp);
 	}
 }
@@ -596,8 +604,8 @@ void process_srcu(struct work_struct *work)
 
 	sp = container_of(work, struct srcu_struct, work.work);
 
-	srcu_advance_batches(sp, 1);
+	srcu_advance_batches(sp);
 	srcu_invoke_callbacks(sp);
-	srcu_reschedule(sp, SRCU_INTERVAL);
+	srcu_reschedule(sp, atomic_read(&sp->srcu_exp_cnt) ? 0 : SRCU_INTERVAL);
 }
 EXPORT_SYMBOL_GPL(process_srcu);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 34/39] mm: Use static initialization for "srcu"
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (32 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 33/39] srcu: Crude control of expedited grace periods Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 35/39] srcu: Create a tiny SRCU Paul E. McKenney
                     ` (5 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney, linux-mm, Michal Hocko,
	Vegard Nossum

The MM-notifier code currently dynamically initializes the srcu_struct
named "srcu" at subsys_initcall() time, and includes a BUG_ON() to check
this initialization in do_mmu_notifier_register().  Unfortunately, there
is no foolproof way to verify that an srcu_struct has been initialized,
given the possibility of an srcu_struct being allocated on the stack or
on the heap.  This means that creating an srcu_struct_is_initialized()
function is not a reasonable course of action.  Nor is peppering
do_mmu_notifier_register() with SRCU-specific #ifdefs an attractive
alternative.

This commit therefore uses DEFINE_STATIC_SRCU() to initialize
this srcu_struct at compile time, thus eliminating both the
subsys_initcall()-time initialization and the runtime BUG_ON().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: <linux-mm@kvack.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Vegard Nossum <vegard.nossum@oracle.com>
---
 mm/mmu_notifier.c | 14 +-------------
 1 file changed, 1 insertion(+), 13 deletions(-)

diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index a7652acd2ab9..54ca54562928 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -21,7 +21,7 @@
 #include <linux/slab.h>
 
 /* global SRCU for all MMs */
-static struct srcu_struct srcu;
+DEFINE_STATIC_SRCU(srcu);
 
 /*
  * This function allows mmu_notifier::release callback to delay a call to
@@ -252,12 +252,6 @@ static int do_mmu_notifier_register(struct mmu_notifier *mn,
 
 	BUG_ON(atomic_read(&mm->mm_users) <= 0);
 
-	/*
-	 * Verify that mmu_notifier_init() already run and the global srcu is
-	 * initialized.
-	 */
-	BUG_ON(!srcu.per_cpu_ref);
-
 	ret = -ENOMEM;
 	mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
 	if (unlikely(!mmu_notifier_mm))
@@ -406,9 +400,3 @@ void mmu_notifier_unregister_no_release(struct mmu_notifier *mn,
 	mmdrop(mm);
 }
 EXPORT_SYMBOL_GPL(mmu_notifier_unregister_no_release);
-
-static int __init mmu_notifier_init(void)
-{
-	return init_srcu_struct(&srcu);
-}
-subsys_initcall(mmu_notifier_init);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 35/39] srcu: Create a tiny SRCU
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (33 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 34/39] mm: Use static initialization for "srcu" Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 36/39] srcutorture: Print Tiny SRCU reader statistics Paul E. McKenney
                     ` (4 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

In response to automated complaints about modifications to SRCU
increasing its size, this commit creates a tiny SRCU that is
used in SMP=n && PREEMPT=n builds.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/srcu.h     |  69 ++-------------
 include/linux/srcutiny.h |  81 ++++++++++++++++++
 include/linux/srcutree.h |  91 ++++++++++++++++++++
 init/Kconfig             |  12 +++
 kernel/rcu/Makefile      |   3 +-
 kernel/rcu/rcutorture.c  |   2 +
 kernel/rcu/srcutiny.c    | 215 +++++++++++++++++++++++++++++++++++++++++++++++
 7 files changed, 411 insertions(+), 62 deletions(-)
 create mode 100644 include/linux/srcutiny.h
 create mode 100644 include/linux/srcutree.h
 create mode 100644 kernel/rcu/srcutiny.c

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 73a1b6296224..907f09b14eda 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -34,28 +34,7 @@
 #include <linux/workqueue.h>
 #include <linux/rcu_segcblist.h>
 
-struct srcu_array {
-	unsigned long lock_count[2];
-	unsigned long unlock_count[2];
-};
-
-struct srcu_struct {
-	unsigned long completed;
-	unsigned long srcu_gp_seq;
-	atomic_t srcu_exp_cnt;
-	struct srcu_array __percpu *per_cpu_ref;
-	spinlock_t queue_lock; /* protect ->srcu_cblist */
-	struct rcu_segcblist srcu_cblist;
-	struct delayed_work work;
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
-	struct lockdep_map dep_map;
-#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
-};
-
-/* Values for -> state variable. */
-#define SRCU_STATE_IDLE		0
-#define SRCU_STATE_SCAN1	1
-#define SRCU_STATE_SCAN2	2
+struct srcu_struct;
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
@@ -77,42 +56,13 @@ int init_srcu_struct(struct srcu_struct *sp);
 #define __SRCU_DEP_MAP_INIT(srcu_name)
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
-void process_srcu(struct work_struct *work);
-
-#define __SRCU_STRUCT_INIT(name)					\
-	{								\
-		.completed = -300,					\
-		.per_cpu_ref = &name##_srcu_array,			\
-		.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock),	\
-		.srcu_cblist = RCU_SEGCBLIST_INITIALIZER(name.srcu_cblist),\
-		.work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
-		__SRCU_DEP_MAP_INIT(name)				\
-	}
-
-/*
- * Define and initialize a srcu struct at build time.
- * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
- *
- * Note that although DEFINE_STATIC_SRCU() hides the name from other
- * files, the per-CPU variable rules nevertheless require that the
- * chosen name be globally unique.  These rules also prohibit use of
- * DEFINE_STATIC_SRCU() within a function.  If these rules are too
- * restrictive, declare the srcu_struct manually.  For example, in
- * each file:
- *
- *	static struct srcu_struct my_srcu;
- *
- * Then, before the first use of each my_srcu, manually initialize it:
- *
- *	init_srcu_struct(&my_srcu);
- *
- * See include/linux/percpu-defs.h for the rules on per-CPU variables.
- */
-#define __DEFINE_SRCU(name, is_static)					\
-	static DEFINE_PER_CPU(struct srcu_array, name##_srcu_array);\
-	is_static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
-#define DEFINE_SRCU(name)		__DEFINE_SRCU(name, /* not static */)
-#define DEFINE_STATIC_SRCU(name)	__DEFINE_SRCU(name, static)
+#ifdef CONFIG_TINY_SRCU
+#include <linux/srcutiny.h>
+#elif defined(CONFIG_TREE_SRCU)
+#include <linux/srcutree.h>
+#else
+#error "Unknown SRCU implementation specified to kernel configuration"
+#endif
 
 /**
  * call_srcu() - Queue a callback for invocation after an SRCU grace period
@@ -138,9 +88,6 @@ void cleanup_srcu_struct(struct srcu_struct *sp);
 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
 void synchronize_srcu(struct srcu_struct *sp);
-void synchronize_srcu_expedited(struct srcu_struct *sp);
-unsigned long srcu_batches_completed(struct srcu_struct *sp);
-void srcu_barrier(struct srcu_struct *sp);
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
new file mode 100644
index 000000000000..4f284e4f4d8c
--- /dev/null
+++ b/include/linux/srcutiny.h
@@ -0,0 +1,81 @@
+/*
+ * Sleepable Read-Copy Update mechanism for mutual exclusion,
+ *	tiny variant.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright (C) IBM Corporation, 2017
+ *
+ * Author: Paul McKenney <paulmck@us.ibm.com>
+ */
+
+#ifndef _LINUX_SRCU_TINY_H
+#define _LINUX_SRCU_TINY_H
+
+#include <linux/swait.h>
+
+struct srcu_struct {
+	int srcu_lock_nesting[2];	/* srcu_read_lock() nesting depth. */
+	struct swait_queue_head srcu_wq;
+					/* Last srcu_read_unlock() wakes GP. */
+	unsigned long srcu_gp_seq;	/* GP seq # for callback tagging. */
+	struct rcu_segcblist srcu_cblist;
+					/* Pending SRCU callbacks. */
+	int srcu_idx;			/* Current reader array element. */
+	bool srcu_gp_running;		/* GP workqueue running? */
+	bool srcu_gp_waiting;		/* GP waiting for readers? */
+	struct work_struct srcu_work;	/* For driving grace periods. */
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	struct lockdep_map dep_map;
+#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+};
+
+void srcu_drive_gp(struct work_struct *wp);
+
+#define __SRCU_STRUCT_INIT(name)					\
+{									\
+	.srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq),	\
+	.srcu_cblist = RCU_SEGCBLIST_INITIALIZER(name.srcu_cblist),	\
+	.srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp),	\
+	__SRCU_DEP_MAP_INIT(name)					\
+}
+
+/*
+ * This odd _STATIC_ arrangement is needed for API compatibility with
+ * Tree SRCU, which needs some per-CPU data.
+ */
+#define DEFINE_SRCU(name) \
+	struct srcu_struct name = __SRCU_STRUCT_INIT(name)
+#define DEFINE_STATIC_SRCU(name) \
+	static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
+
+void synchronize_srcu(struct srcu_struct *sp);
+
+static inline void synchronize_srcu_expedited(struct srcu_struct *sp)
+{
+	synchronize_srcu(sp);
+}
+
+static inline void srcu_barrier(struct srcu_struct *sp)
+{
+	synchronize_srcu(sp);
+}
+
+static inline unsigned long srcu_batches_completed(struct srcu_struct *sp)
+{
+	return 0;
+}
+
+#endif
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
new file mode 100644
index 000000000000..f2b3bd6c6bc2
--- /dev/null
+++ b/include/linux/srcutree.h
@@ -0,0 +1,91 @@
+/*
+ * Sleepable Read-Copy Update mechanism for mutual exclusion,
+ *	tree variant.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright (C) IBM Corporation, 2017
+ *
+ * Author: Paul McKenney <paulmck@us.ibm.com>
+ */
+
+#ifndef _LINUX_SRCU_TREE_H
+#define _LINUX_SRCU_TREE_H
+
+struct srcu_array {
+	unsigned long lock_count[2];
+	unsigned long unlock_count[2];
+};
+
+struct srcu_struct {
+	unsigned long completed;
+	unsigned long srcu_gp_seq;
+	atomic_t srcu_exp_cnt;
+	struct srcu_array __percpu *per_cpu_ref;
+	spinlock_t queue_lock; /* protect ->srcu_cblist */
+	struct rcu_segcblist srcu_cblist;
+	struct delayed_work work;
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	struct lockdep_map dep_map;
+#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+};
+
+/* Values for -> state variable. */
+#define SRCU_STATE_IDLE		0
+#define SRCU_STATE_SCAN1	1
+#define SRCU_STATE_SCAN2	2
+
+void process_srcu(struct work_struct *work);
+
+#define __SRCU_STRUCT_INIT(name)					\
+	{								\
+		.completed = -300,					\
+		.per_cpu_ref = &name##_srcu_array,			\
+		.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock),	\
+		.srcu_cblist = RCU_SEGCBLIST_INITIALIZER(name.srcu_cblist),\
+		.work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
+		__SRCU_DEP_MAP_INIT(name)				\
+	}
+
+/*
+ * Define and initialize a srcu struct at build time.
+ * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
+ *
+ * Note that although DEFINE_STATIC_SRCU() hides the name from other
+ * files, the per-CPU variable rules nevertheless require that the
+ * chosen name be globally unique.  These rules also prohibit use of
+ * DEFINE_STATIC_SRCU() within a function.  If these rules are too
+ * restrictive, declare the srcu_struct manually.  For example, in
+ * each file:
+ *
+ *	static struct srcu_struct my_srcu;
+ *
+ * Then, before the first use of each my_srcu, manually initialize it:
+ *
+ *	init_srcu_struct(&my_srcu);
+ *
+ * See include/linux/percpu-defs.h for the rules on per-CPU variables.
+ */
+#define __DEFINE_SRCU(name, is_static)					\
+	static DEFINE_PER_CPU(struct srcu_array, name##_srcu_array);\
+	is_static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
+#define DEFINE_SRCU(name)		__DEFINE_SRCU(name, /* not static */)
+#define DEFINE_STATIC_SRCU(name)	__DEFINE_SRCU(name, static)
+
+void synchronize_srcu_expedited(struct srcu_struct *sp);
+void srcu_barrier(struct srcu_struct *sp);
+unsigned long srcu_batches_completed(struct srcu_struct *sp);
+
+#endif
diff --git a/init/Kconfig b/init/Kconfig
index a92f27da4a27..d269f2ca17b8 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -526,6 +526,18 @@ config SRCU
 	  permits arbitrary sleeping or blocking within RCU read-side critical
 	  sections.
 
+config TINY_SRCU
+	bool
+	default y if TINY_RCU
+	help
+	  This option selects the single-CPU non-preemptible version of SRCU.
+
+config TREE_SRCU
+	bool
+	default y if !TINY_RCU
+	help
+	  This option selects the full-fledged version of SRCU.
+
 config TASKS_RCU
 	bool
 	default n
diff --git a/kernel/rcu/Makefile b/kernel/rcu/Makefile
index 18dfc485225c..b853214a2b99 100644
--- a/kernel/rcu/Makefile
+++ b/kernel/rcu/Makefile
@@ -3,7 +3,8 @@
 KCOV_INSTRUMENT := n
 
 obj-y += update.o sync.o
-obj-$(CONFIG_SRCU) += srcu.o
+obj-$(CONFIG_TREE_SRCU) += srcu.o
+obj-$(CONFIG_TINY_SRCU) += srcutiny.o
 obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
 obj-$(CONFIG_RCU_PERF_TEST) += rcuperf.o
 obj-$(CONFIG_TREE_RCU) += tree.o
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index cccc417a8135..98591e16db1a 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -559,6 +559,7 @@ static void srcu_torture_barrier(void)
 
 static void srcu_torture_stats(void)
 {
+#ifdef CONFIG_TREE_SRCU
 	int cpu;
 	int idx = srcu_ctlp->completed & 0x1;
 
@@ -587,6 +588,7 @@ static void srcu_torture_stats(void)
 		pr_cont(" %d(%ld,%ld)", cpu, c0, c1);
 	}
 	pr_cont("\n");
+#endif
 }
 
 static void srcu_torture_synchronize_expedited(void)
diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
new file mode 100644
index 000000000000..b8293527ee18
--- /dev/null
+++ b/kernel/rcu/srcutiny.c
@@ -0,0 +1,215 @@
+/*
+ * Sleepable Read-Copy Update mechanism for mutual exclusion,
+ *	tiny version for non-preemptible single-CPU use.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright (C) IBM Corporation, 2017
+ *
+ * Author: Paul McKenney <paulmck@us.ibm.com>
+ */
+
+#include <linux/export.h>
+#include <linux/mutex.h>
+#include <linux/preempt.h>
+#include <linux/rcupdate_wait.h>
+#include <linux/sched.h>
+#include <linux/delay.h>
+#include <linux/srcu.h>
+
+#include <linux/rcu_node_tree.h>
+#include "rcu.h"
+
+static int init_srcu_struct_fields(struct srcu_struct *sp)
+{
+	sp->srcu_lock_nesting[0] = 0;
+	sp->srcu_lock_nesting[1] = 0;
+	init_swait_queue_head(&sp->srcu_wq);
+	sp->srcu_gp_seq = 0;
+	rcu_segcblist_init(&sp->srcu_cblist);
+	sp->srcu_gp_running = false;
+	sp->srcu_gp_waiting = false;
+	sp->srcu_idx = 0;
+	INIT_WORK(&sp->srcu_work, srcu_drive_gp);
+	return 0;
+}
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+
+int __init_srcu_struct(struct srcu_struct *sp, const char *name,
+		       struct lock_class_key *key)
+{
+	/* Don't re-initialize a lock while it is held. */
+	debug_check_no_locks_freed((void *)sp, sizeof(*sp));
+	lockdep_init_map(&sp->dep_map, name, key, 0);
+	return init_srcu_struct_fields(sp);
+}
+EXPORT_SYMBOL_GPL(__init_srcu_struct);
+
+#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+/*
+ * init_srcu_struct - initialize a sleep-RCU structure
+ * @sp: structure to initialize.
+ *
+ * Must invoke this on a given srcu_struct before passing that srcu_struct
+ * to any other function.  Each srcu_struct represents a separate domain
+ * of SRCU protection.
+ */
+int init_srcu_struct(struct srcu_struct *sp)
+{
+	return init_srcu_struct_fields(sp);
+}
+EXPORT_SYMBOL_GPL(init_srcu_struct);
+
+#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+/*
+ * cleanup_srcu_struct - deconstruct a sleep-RCU structure
+ * @sp: structure to clean up.
+ *
+ * Must invoke this after you are finished using a given srcu_struct that
+ * was initialized via init_srcu_struct(), else you leak memory.
+ */
+void cleanup_srcu_struct(struct srcu_struct *sp)
+{
+	WARN_ON(sp->srcu_lock_nesting[0] || sp->srcu_lock_nesting[1]);
+	flush_work(&sp->srcu_work);
+	WARN_ON(rcu_seq_state(sp->srcu_gp_seq));
+	WARN_ON(sp->srcu_gp_running);
+	WARN_ON(sp->srcu_gp_waiting);
+	WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist));
+}
+EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
+
+/*
+ * Counts the new reader in the appropriate per-CPU element of the
+ * srcu_struct.  Must be called from process context.
+ * Returns an index that must be passed to the matching srcu_read_unlock().
+ */
+int __srcu_read_lock(struct srcu_struct *sp)
+{
+	int idx;
+
+	idx = READ_ONCE(sp->srcu_idx);
+	WRITE_ONCE(sp->srcu_lock_nesting[idx], sp->srcu_lock_nesting[idx] + 1);
+	return idx;
+}
+EXPORT_SYMBOL_GPL(__srcu_read_lock);
+
+/*
+ * Removes the count for the old reader from the appropriate element of
+ * the srcu_struct.  Must be called from process context.
+ */
+void __srcu_read_unlock(struct srcu_struct *sp, int idx)
+{
+	int newval = sp->srcu_lock_nesting[idx] - 1;
+
+	WRITE_ONCE(sp->srcu_lock_nesting[idx], newval);
+	if (!newval && READ_ONCE(sp->srcu_gp_waiting))
+		swake_up(&sp->srcu_wq);
+}
+EXPORT_SYMBOL_GPL(__srcu_read_unlock);
+
+/*
+ * Workqueue handler to drive one grace period and invoke any callbacks
+ * that become ready as a result.  Single-CPU and !PREEMPT operation
+ * means that we get away with murder on synchronization.  ;-)
+ */
+void srcu_drive_gp(struct work_struct *wp)
+{
+	int idx;
+	struct rcu_cblist ready_cbs;
+	struct srcu_struct *sp;
+	struct rcu_head *rhp;
+
+	sp = container_of(wp, struct srcu_struct, srcu_work);
+	if (sp->srcu_gp_running || rcu_segcblist_empty(&sp->srcu_cblist))
+		return; /* Already running or nothing to do. */
+
+	/* Tag recently arrived callbacks and wait for readers. */
+	WRITE_ONCE(sp->srcu_gp_running, true);
+	rcu_segcblist_accelerate(&sp->srcu_cblist,
+				 rcu_seq_snap(&sp->srcu_gp_seq));
+	rcu_seq_start(&sp->srcu_gp_seq);
+	idx = sp->srcu_idx;
+	WRITE_ONCE(sp->srcu_idx, !sp->srcu_idx);
+	WRITE_ONCE(sp->srcu_gp_waiting, true);  /* srcu_read_unlock() wakes! */
+	swait_event(sp->srcu_wq, !READ_ONCE(sp->srcu_lock_nesting[idx]));
+	WRITE_ONCE(sp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
+	rcu_seq_end(&sp->srcu_gp_seq);
+
+	/* Update callback list based on GP, and invoke ready callbacks. */
+	rcu_segcblist_advance(&sp->srcu_cblist,
+			      rcu_seq_current(&sp->srcu_gp_seq));
+	if (rcu_segcblist_ready_cbs(&sp->srcu_cblist)) {
+		rcu_cblist_init(&ready_cbs);
+		local_irq_disable();
+		rcu_segcblist_extract_done_cbs(&sp->srcu_cblist, &ready_cbs);
+		local_irq_enable();
+		rhp = rcu_cblist_dequeue(&ready_cbs);
+		for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
+			local_bh_disable();
+			rhp->func(rhp);
+			local_bh_enable();
+		}
+		local_irq_disable();
+		rcu_segcblist_insert_count(&sp->srcu_cblist, &ready_cbs);
+		local_irq_enable();
+	}
+	WRITE_ONCE(sp->srcu_gp_running, false);
+
+	/*
+	 * If more callbacks, reschedule ourselves.  This can race with
+	 * a call_srcu() at interrupt level, but the ->srcu_gp_running
+	 * checks will straighten that out.
+	 */
+	if (!rcu_segcblist_empty(&sp->srcu_cblist))
+		schedule_work(&sp->srcu_work);
+}
+EXPORT_SYMBOL_GPL(srcu_drive_gp);
+
+/*
+ * Enqueue an SRCU callback on the specified srcu_struct structure,
+ * initiating grace-period processing if it is not already running.
+ */
+void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
+	       rcu_callback_t func)
+{
+	unsigned long flags;
+
+	head->func = func;
+	local_irq_save(flags);
+	rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
+	local_irq_restore(flags);
+	if (!READ_ONCE(sp->srcu_gp_running))
+		schedule_work(&sp->srcu_work);
+}
+EXPORT_SYMBOL_GPL(call_srcu);
+
+/*
+ * synchronize_srcu - wait for prior SRCU read-side critical-section completion
+ */
+void synchronize_srcu(struct srcu_struct *sp)
+{
+	struct rcu_synchronize rs;
+
+	init_rcu_head_on_stack(&rs.head);
+	init_completion(&rs.completion);
+	call_srcu(sp, &rs.head, wakeme_after_rcu);
+	wait_for_completion(&rs.completion);
+	destroy_rcu_head_on_stack(&rs.head);
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 36/39] srcutorture: Print Tiny SRCU reader statistics
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (34 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 35/39] srcu: Create a tiny SRCU Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 37/39] srcu: Introduce CLASSIC_SRCU Kconfig option Paul E. McKenney
                     ` (3 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The srcu_torture_stats() function is adapted to the specific srcu_struct
layout traditionally used by SRCU.  This commit therefore adds support
for Tiny SRCU.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcutorture.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 98591e16db1a..9cbb8a7b909d 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -559,11 +559,12 @@ static void srcu_torture_barrier(void)
 
 static void srcu_torture_stats(void)
 {
-#ifdef CONFIG_TREE_SRCU
-	int cpu;
-	int idx = srcu_ctlp->completed & 0x1;
+	int __maybe_unused cpu;
+	int idx;
 
-	pr_alert("%s%s per-CPU(idx=%d):",
+#ifdef CONFIG_TREE_SRCU
+	idx = srcu_ctlp->completed & 0x1;
+	pr_alert("%s%s Tree SRCU per-CPU(idx=%d):",
 		 torture_type, TORTURE_FLAG, idx);
 	for_each_possible_cpu(cpu) {
 		unsigned long l0, l1;
@@ -588,6 +589,12 @@ static void srcu_torture_stats(void)
 		pr_cont(" %d(%ld,%ld)", cpu, c0, c1);
 	}
 	pr_cont("\n");
+#elif defined(CONFIG_TINY_SRCU)
+	idx = READ_ONCE(srcu_ctlp->srcu_idx) & 0x1;
+	pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%d,%d)\n",
+		 torture_type, TORTURE_FLAG, idx,
+		 READ_ONCE(srcu_ctlp->srcu_lock_nesting[!idx]),
+		 READ_ONCE(srcu_ctlp->srcu_lock_nesting[idx]));
 #endif
 }
 
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 37/39] srcu: Introduce CLASSIC_SRCU Kconfig option
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (35 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 36/39] srcutorture: Print Tiny SRCU reader statistics Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 38/39] srcu: Parallelize callback handling Paul E. McKenney
                     ` (2 subsequent siblings)
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

The TREE_SRCU rewrite is large and a bit on the non-simple side, so
this commit helps reduce risk by allowing the old v4.11 SRCU algorithm
to be selected using a new CLASSIC_SRCU Kconfig option that depends
on RCU_EXPERT.  The default is to use the new TREE_SRCU and TINY_SRCU
algorithms, in order to help get these the testing that they need.
However, if your users do not require the update-side scalability that
is to be provided by TREE_SRCU, select RCU_EXPERT and then CLASSIC_SRCU
to revert back to the old classic SRCU algorithm.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/srcu.h        |   2 +
 include/linux/srcuclassic.h | 101 ++++++++
 init/Kconfig                |  21 +-
 kernel/rcu/Makefile         |   3 +-
 kernel/rcu/rcutorture.c     |   2 +-
 kernel/rcu/srcu.c           | 347 ++++++++++++++-----------
 kernel/rcu/srcutree.c       | 613 ++++++++++++++++++++++++++++++++++++++++++++
 7 files changed, 934 insertions(+), 155 deletions(-)
 create mode 100644 include/linux/srcuclassic.h
 create mode 100644 kernel/rcu/srcutree.c

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 907f09b14eda..167ad8831aaf 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -60,6 +60,8 @@ int init_srcu_struct(struct srcu_struct *sp);
 #include <linux/srcutiny.h>
 #elif defined(CONFIG_TREE_SRCU)
 #include <linux/srcutree.h>
+#elif defined(CONFIG_CLASSIC_SRCU)
+#include <linux/srcuclassic.h>
 #else
 #error "Unknown SRCU implementation specified to kernel configuration"
 #endif
diff --git a/include/linux/srcuclassic.h b/include/linux/srcuclassic.h
new file mode 100644
index 000000000000..41cf99930f34
--- /dev/null
+++ b/include/linux/srcuclassic.h
@@ -0,0 +1,101 @@
+/*
+ * Sleepable Read-Copy Update mechanism for mutual exclusion,
+ *	classic v4.11 variant.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright (C) IBM Corporation, 2017
+ *
+ * Author: Paul McKenney <paulmck@us.ibm.com>
+ */
+
+#ifndef _LINUX_SRCU_CLASSIC_H
+#define _LINUX_SRCU_CLASSIC_H
+
+struct srcu_array {
+	unsigned long lock_count[2];
+	unsigned long unlock_count[2];
+};
+
+struct rcu_batch {
+	struct rcu_head *head, **tail;
+};
+
+#define RCU_BATCH_INIT(name) { NULL, &(name.head) }
+
+struct srcu_struct {
+	unsigned long completed;
+	struct srcu_array __percpu *per_cpu_ref;
+	spinlock_t queue_lock; /* protect ->batch_queue, ->running */
+	bool running;
+	/* callbacks just queued */
+	struct rcu_batch batch_queue;
+	/* callbacks try to do the first check_zero */
+	struct rcu_batch batch_check0;
+	/* callbacks done with the first check_zero and the flip */
+	struct rcu_batch batch_check1;
+	struct rcu_batch batch_done;
+	struct delayed_work work;
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	struct lockdep_map dep_map;
+#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+};
+
+void process_srcu(struct work_struct *work);
+
+#define __SRCU_STRUCT_INIT(name)					\
+	{								\
+		.completed = -300,					\
+		.per_cpu_ref = &name##_srcu_array,			\
+		.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock),	\
+		.running = false,					\
+		.batch_queue = RCU_BATCH_INIT(name.batch_queue),	\
+		.batch_check0 = RCU_BATCH_INIT(name.batch_check0),	\
+		.batch_check1 = RCU_BATCH_INIT(name.batch_check1),	\
+		.batch_done = RCU_BATCH_INIT(name.batch_done),		\
+		.work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
+		__SRCU_DEP_MAP_INIT(name)				\
+	}
+
+/*
+ * Define and initialize a srcu struct at build time.
+ * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
+ *
+ * Note that although DEFINE_STATIC_SRCU() hides the name from other
+ * files, the per-CPU variable rules nevertheless require that the
+ * chosen name be globally unique.  These rules also prohibit use of
+ * DEFINE_STATIC_SRCU() within a function.  If these rules are too
+ * restrictive, declare the srcu_struct manually.  For example, in
+ * each file:
+ *
+ *	static struct srcu_struct my_srcu;
+ *
+ * Then, before the first use of each my_srcu, manually initialize it:
+ *
+ *	init_srcu_struct(&my_srcu);
+ *
+ * See include/linux/percpu-defs.h for the rules on per-CPU variables.
+ */
+#define __DEFINE_SRCU(name, is_static)					\
+	static DEFINE_PER_CPU(struct srcu_array, name##_srcu_array);\
+	is_static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
+#define DEFINE_SRCU(name)		__DEFINE_SRCU(name, /* not static */)
+#define DEFINE_STATIC_SRCU(name)	__DEFINE_SRCU(name, static)
+
+void synchronize_srcu_expedited(struct srcu_struct *sp);
+void srcu_barrier(struct srcu_struct *sp);
+unsigned long srcu_batches_completed(struct srcu_struct *sp);
+
+#endif
diff --git a/init/Kconfig b/init/Kconfig
index d269f2ca17b8..558cc3638ab9 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -526,15 +526,32 @@ config SRCU
 	  permits arbitrary sleeping or blocking within RCU read-side critical
 	  sections.
 
+config CLASSIC_SRCU
+	bool "Use v4.11 classic SRCU implementation"
+	default n
+	depends on RCU_EXPERT && SRCU
+	help
+	  This option selects the traditional well-tested classic SRCU
+	  implementation from v4.11, as might be desired for enterprise
+	  Linux distributions.  Without this option, the shiny new
+	  Tiny SRCU and Tree SRCU implementations are used instead.
+	  At some point, it is hoped that Tiny SRCU and Tree SRCU
+	  will accumulate enough test time and confidence to allow
+	  Classic SRCU to be dropped entirely.
+
+	  Say Y if you need a rock-solid SRCU.
+
+	  Say N if you would like help test Tree SRCU.
+
 config TINY_SRCU
 	bool
-	default y if TINY_RCU
+	default y if TINY_RCU && !CLASSIC_SRCU
 	help
 	  This option selects the single-CPU non-preemptible version of SRCU.
 
 config TREE_SRCU
 	bool
-	default y if !TINY_RCU
+	default y if !TINY_RCU && !CLASSIC_SRCU
 	help
 	  This option selects the full-fledged version of SRCU.
 
diff --git a/kernel/rcu/Makefile b/kernel/rcu/Makefile
index b853214a2b99..158e6593d58c 100644
--- a/kernel/rcu/Makefile
+++ b/kernel/rcu/Makefile
@@ -3,7 +3,8 @@
 KCOV_INSTRUMENT := n
 
 obj-y += update.o sync.o
-obj-$(CONFIG_TREE_SRCU) += srcu.o
+obj-$(CONFIG_CLASSIC_SRCU) += srcu.o
+obj-$(CONFIG_TREE_SRCU) += srcutree.o
 obj-$(CONFIG_TINY_SRCU) += srcutiny.o
 obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
 obj-$(CONFIG_RCU_PERF_TEST) += rcuperf.o
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 9cbb8a7b909d..6f344b6748a8 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -562,7 +562,7 @@ static void srcu_torture_stats(void)
 	int __maybe_unused cpu;
 	int idx;
 
-#ifdef CONFIG_TREE_SRCU
+#if defined(CONFIG_TREE_SRCU) || defined(CONFIG_CLASSIC_SRCU)
 	idx = srcu_ctlp->completed & 0x1;
 	pr_alert("%s%s Tree SRCU per-CPU(idx=%d):",
 		 torture_type, TORTURE_FLAG, idx);
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index b62919be99e7..1b11a7c3203e 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -36,16 +36,75 @@
 #include <linux/delay.h>
 #include <linux/srcu.h>
 
-#include <linux/rcu_node_tree.h>
 #include "rcu.h"
 
+/*
+ * Initialize an rcu_batch structure to empty.
+ */
+static inline void rcu_batch_init(struct rcu_batch *b)
+{
+	b->head = NULL;
+	b->tail = &b->head;
+}
+
+/*
+ * Enqueue a callback onto the tail of the specified rcu_batch structure.
+ */
+static inline void rcu_batch_queue(struct rcu_batch *b, struct rcu_head *head)
+{
+	*b->tail = head;
+	b->tail = &head->next;
+}
+
+/*
+ * Is the specified rcu_batch structure empty?
+ */
+static inline bool rcu_batch_empty(struct rcu_batch *b)
+{
+	return b->tail == &b->head;
+}
+
+/*
+ * Remove the callback at the head of the specified rcu_batch structure
+ * and return a pointer to it, or return NULL if the structure is empty.
+ */
+static inline struct rcu_head *rcu_batch_dequeue(struct rcu_batch *b)
+{
+	struct rcu_head *head;
+
+	if (rcu_batch_empty(b))
+		return NULL;
+
+	head = b->head;
+	b->head = head->next;
+	if (b->tail == &head->next)
+		rcu_batch_init(b);
+
+	return head;
+}
+
+/*
+ * Move all callbacks from the rcu_batch structure specified by "from" to
+ * the structure specified by "to".
+ */
+static inline void rcu_batch_move(struct rcu_batch *to, struct rcu_batch *from)
+{
+	if (!rcu_batch_empty(from)) {
+		*to->tail = from->head;
+		to->tail = from->tail;
+		rcu_batch_init(from);
+	}
+}
+
 static int init_srcu_struct_fields(struct srcu_struct *sp)
 {
 	sp->completed = 0;
-	sp->srcu_gp_seq = 0;
-	atomic_set(&sp->srcu_exp_cnt, 0);
 	spin_lock_init(&sp->queue_lock);
-	rcu_segcblist_init(&sp->srcu_cblist);
+	sp->running = false;
+	rcu_batch_init(&sp->batch_queue);
+	rcu_batch_init(&sp->batch_check0);
+	rcu_batch_init(&sp->batch_check1);
+	rcu_batch_init(&sp->batch_done);
 	INIT_DELAYED_WORK(&sp->work, process_srcu);
 	sp->per_cpu_ref = alloc_percpu(struct srcu_array);
 	return sp->per_cpu_ref ? 0 : -ENOMEM;
@@ -180,8 +239,6 @@ static bool srcu_readers_active(struct srcu_struct *sp)
 	return sum;
 }
 
-#define SRCU_INTERVAL		1
-
 /**
  * cleanup_srcu_struct - deconstruct a sleep-RCU structure
  * @sp: structure to clean up.
@@ -191,16 +248,8 @@ static bool srcu_readers_active(struct srcu_struct *sp)
  */
 void cleanup_srcu_struct(struct srcu_struct *sp)
 {
-	WARN_ON_ONCE(atomic_read(&sp->srcu_exp_cnt));
 	if (WARN_ON(srcu_readers_active(sp)))
 		return; /* Leakage unless caller handles error. */
-	if (WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist)))
-		return; /* Leakage unless caller handles error. */
-	flush_delayed_work(&sp->work);
-	if (WARN_ON(rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) != SRCU_STATE_IDLE)) {
-		pr_info("cleanup_srcu_struct: Active srcu_struct %lu CBs %c state: %d\n", rcu_segcblist_n_cbs(&sp->srcu_cblist), ".E"[rcu_segcblist_empty(&sp->srcu_cblist)], rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)));
-		return; /* Caller forgot to stop doing call_srcu()? */
-	}
 	free_percpu(sp->per_cpu_ref);
 	sp->per_cpu_ref = NULL;
 }
@@ -239,36 +288,26 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
  * We use an adaptive strategy for synchronize_srcu() and especially for
  * synchronize_srcu_expedited().  We spin for a fixed time period
  * (defined below) to allow SRCU readers to exit their read-side critical
- * sections.  If there are still some readers after a few microseconds,
- * we repeatedly block for 1-millisecond time periods.
+ * sections.  If there are still some readers after 10 microseconds,
+ * we repeatedly block for 1-millisecond time periods.  This approach
+ * has done well in testing, so there is no need for a config parameter.
  */
 #define SRCU_RETRY_CHECK_DELAY		5
+#define SYNCHRONIZE_SRCU_TRYCOUNT	2
+#define SYNCHRONIZE_SRCU_EXP_TRYCOUNT	12
 
 /*
- * Start an SRCU grace period.
- */
-static void srcu_gp_start(struct srcu_struct *sp)
-{
-	int state;
-
-	rcu_segcblist_accelerate(&sp->srcu_cblist,
-				 rcu_seq_snap(&sp->srcu_gp_seq));
-	rcu_seq_start(&sp->srcu_gp_seq);
-	state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
-	WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
-}
-
-/*
- * Wait until all readers counted by array index idx complete, but
- * loop an additional time if there is an expedited grace period pending.
- * The caller must ensure that ->completed is not changed while checking.
+ * @@@ Wait until all pre-existing readers complete.  Such readers
+ * will have used the index specified by "idx".
+ * the caller should ensures the ->completed is not changed while checking
+ * and idx = (->completed & 1) ^ 1
  */
 static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
 {
 	for (;;) {
 		if (srcu_readers_active_idx_check(sp, idx))
 			return true;
-		if (--trycount + !!atomic_read(&sp->srcu_exp_cnt) <= 0)
+		if (--trycount <= 0)
 			return false;
 		udelay(SRCU_RETRY_CHECK_DELAY);
 	}
@@ -294,19 +333,6 @@ static void srcu_flip(struct srcu_struct *sp)
 }
 
 /*
- * End an SRCU grace period.
- */
-static void srcu_gp_end(struct srcu_struct *sp)
-{
-	rcu_seq_end(&sp->srcu_gp_seq);
-
-	spin_lock_irq(&sp->queue_lock);
-	rcu_segcblist_advance(&sp->srcu_cblist,
-			      rcu_seq_current(&sp->srcu_gp_seq));
-	spin_unlock_irq(&sp->queue_lock);
-}
-
-/*
  * Enqueue an SRCU callback on the specified srcu_struct structure,
  * initiating grace-period processing if it is not already running.
  *
@@ -342,24 +368,26 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 	head->func = func;
 	spin_lock_irqsave(&sp->queue_lock, flags);
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
-	rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
-	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
-		srcu_gp_start(sp);
+	rcu_batch_queue(&sp->batch_queue, head);
+	if (!sp->running) {
+		sp->running = true;
 		queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
 	}
 	spin_unlock_irqrestore(&sp->queue_lock, flags);
 }
 EXPORT_SYMBOL_GPL(call_srcu);
 
-static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay);
+static void srcu_advance_batches(struct srcu_struct *sp, int trycount);
+static void srcu_reschedule(struct srcu_struct *sp);
 
 /*
  * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
  */
-static void __synchronize_srcu(struct srcu_struct *sp)
+static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 {
 	struct rcu_synchronize rcu;
 	struct rcu_head *head = &rcu.head;
+	bool done = false;
 
 	RCU_LOCKDEP_WARN(lock_is_held(&sp->dep_map) ||
 			 lock_is_held(&rcu_bh_lock_map) ||
@@ -367,8 +395,6 @@ static void __synchronize_srcu(struct srcu_struct *sp)
 			 lock_is_held(&rcu_sched_lock_map),
 			 "Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");
 
-	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
-		return;
 	might_sleep();
 	init_completion(&rcu.completion);
 
@@ -376,47 +402,31 @@ static void __synchronize_srcu(struct srcu_struct *sp)
 	head->func = wakeme_after_rcu;
 	spin_lock_irq(&sp->queue_lock);
 	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
-	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
+	if (!sp->running) {
 		/* steal the processing owner */
-		rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
-		srcu_gp_start(sp);
+		sp->running = true;
+		rcu_batch_queue(&sp->batch_check0, head);
 		spin_unlock_irq(&sp->queue_lock);
+
+		srcu_advance_batches(sp, trycount);
+		if (!rcu_batch_empty(&sp->batch_done)) {
+			BUG_ON(sp->batch_done.head != head);
+			rcu_batch_dequeue(&sp->batch_done);
+			done = true;
+		}
 		/* give the processing owner to work_struct */
-		srcu_reschedule(sp, 0);
+		srcu_reschedule(sp);
 	} else {
-		rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
+		rcu_batch_queue(&sp->batch_queue, head);
 		spin_unlock_irq(&sp->queue_lock);
 	}
 
-	wait_for_completion(&rcu.completion);
-	smp_mb(); /* Caller's later accesses after GP. */
-}
-
-/**
- * synchronize_srcu_expedited - Brute-force SRCU grace period
- * @sp: srcu_struct with which to synchronize.
- *
- * Wait for an SRCU grace period to elapse, but be more aggressive about
- * spinning rather than blocking when waiting.
- *
- * Note that synchronize_srcu_expedited() has the same deadlock and
- * memory-ordering properties as does synchronize_srcu().
- */
-void synchronize_srcu_expedited(struct srcu_struct *sp)
-{
-	bool do_norm = rcu_gp_is_normal();
-
-	if (!do_norm) {
-		atomic_inc(&sp->srcu_exp_cnt);
-		smp_mb__after_atomic(); /* increment before GP. */
-	}
-	__synchronize_srcu(sp);
-	if (!do_norm) {
-		smp_mb__before_atomic(); /* GP before decrement. */
-		atomic_dec(&sp->srcu_exp_cnt);
+	if (!done) {
+		wait_for_completion(&rcu.completion);
+		smp_mb(); /* Caller's later accesses after GP. */
 	}
+
 }
-EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
 
 /**
  * synchronize_srcu - wait for prior SRCU read-side critical-section completion
@@ -459,14 +469,29 @@ EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
  */
 void synchronize_srcu(struct srcu_struct *sp)
 {
-	if (rcu_gp_is_expedited())
-		synchronize_srcu_expedited(sp);
-	else
-		__synchronize_srcu(sp);
+	__synchronize_srcu(sp, (rcu_gp_is_expedited() && !rcu_gp_is_normal())
+			   ? SYNCHRONIZE_SRCU_EXP_TRYCOUNT
+			   : SYNCHRONIZE_SRCU_TRYCOUNT);
 }
 EXPORT_SYMBOL_GPL(synchronize_srcu);
 
 /**
+ * synchronize_srcu_expedited - Brute-force SRCU grace period
+ * @sp: srcu_struct with which to synchronize.
+ *
+ * Wait for an SRCU grace period to elapse, but be more aggressive about
+ * spinning rather than blocking when waiting.
+ *
+ * Note that synchronize_srcu_expedited() has the same deadlock and
+ * memory-ordering properties as does synchronize_srcu().
+ */
+void synchronize_srcu_expedited(struct srcu_struct *sp)
+{
+	__synchronize_srcu(sp, SYNCHRONIZE_SRCU_EXP_TRYCOUNT);
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
+
+/**
  * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
  * @sp: srcu_struct on which to wait for in-flight callbacks.
  */
@@ -489,13 +514,29 @@ unsigned long srcu_batches_completed(struct srcu_struct *sp)
 }
 EXPORT_SYMBOL_GPL(srcu_batches_completed);
 
+#define SRCU_CALLBACK_BATCH	10
+#define SRCU_INTERVAL		1
+
+/*
+ * Move any new SRCU callbacks to the first stage of the SRCU grace
+ * period pipeline.
+ */
+static void srcu_collect_new(struct srcu_struct *sp)
+{
+	if (!rcu_batch_empty(&sp->batch_queue)) {
+		spin_lock_irq(&sp->queue_lock);
+		rcu_batch_move(&sp->batch_check0, &sp->batch_queue);
+		spin_unlock_irq(&sp->queue_lock);
+	}
+}
+
 /*
  * Core SRCU state machine.  Advance callbacks from ->batch_check0 to
  * ->batch_check1 and then to ->batch_done as readers drain.
  */
-static void srcu_advance_batches(struct srcu_struct *sp)
+static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
 {
-	int idx;
+	int idx = 1 ^ (sp->completed & 1);
 
 	/*
 	 * Because readers might be delayed for an extended period after
@@ -503,44 +544,50 @@ static void srcu_advance_batches(struct srcu_struct *sp)
 	 * might well be readers using both idx=0 and idx=1.  We therefore
 	 * need to wait for readers to clear from both index values before
 	 * invoking a callback.
-	 *
-	 * The load-acquire ensures that we see the accesses performed
-	 * by the prior grace period.
 	 */
-	idx = rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq)); /* ^^^ */
-	if (idx == SRCU_STATE_IDLE) {
-		spin_lock_irq(&sp->queue_lock);
-		if (rcu_segcblist_empty(&sp->srcu_cblist)) {
-			spin_unlock_irq(&sp->queue_lock);
-			return;
-		}
-		idx = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
-		if (idx == SRCU_STATE_IDLE)
-			srcu_gp_start(sp);
-		spin_unlock_irq(&sp->queue_lock);
-		if (idx != SRCU_STATE_IDLE)
-			return; /* Someone else started the grace period. */
-	}
 
-	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
-		idx = 1 ^ (sp->completed & 1);
-		if (!try_check_zero(sp, idx, 1))
-			return; /* readers present, retry later. */
-		srcu_flip(sp);
-		rcu_seq_set_state(&sp->srcu_gp_seq, SRCU_STATE_SCAN2);
-	}
+	if (rcu_batch_empty(&sp->batch_check0) &&
+	    rcu_batch_empty(&sp->batch_check1))
+		return; /* no callbacks need to be advanced */
 
-	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN2) {
+	if (!try_check_zero(sp, idx, trycount))
+		return; /* failed to advance, will try after SRCU_INTERVAL */
 
-		/*
-		 * SRCU read-side critical sections are normally short,
-		 * so check at least twice in quick succession after a flip.
-		 */
-		idx = 1 ^ (sp->completed & 1);
-		if (!try_check_zero(sp, idx, 2))
-			return; /* readers present, retry after later. */
-		srcu_gp_end(sp);
-	}
+	/*
+	 * The callbacks in ->batch_check1 have already done with their
+	 * first zero check and flip back when they were enqueued on
+	 * ->batch_check0 in a previous invocation of srcu_advance_batches().
+	 * (Presumably try_check_zero() returned false during that
+	 * invocation, leaving the callbacks stranded on ->batch_check1.)
+	 * They are therefore ready to invoke, so move them to ->batch_done.
+	 */
+	rcu_batch_move(&sp->batch_done, &sp->batch_check1);
+
+	if (rcu_batch_empty(&sp->batch_check0))
+		return; /* no callbacks need to be advanced */
+	srcu_flip(sp);
+
+	/*
+	 * The callbacks in ->batch_check0 just finished their
+	 * first check zero and flip, so move them to ->batch_check1
+	 * for future checking on the other idx.
+	 */
+	rcu_batch_move(&sp->batch_check1, &sp->batch_check0);
+
+	/*
+	 * SRCU read-side critical sections are normally short, so check
+	 * at least twice in quick succession after a flip.
+	 */
+	trycount = trycount < 2 ? 2 : trycount;
+	if (!try_check_zero(sp, idx^1, trycount))
+		return; /* failed to advance, will try after SRCU_INTERVAL */
+
+	/*
+	 * The callbacks in ->batch_check1 have now waited for all
+	 * pre-existing readers using both idx values.  They are therefore
+	 * ready to invoke, so move them to ->batch_done.
+	 */
+	rcu_batch_move(&sp->batch_done, &sp->batch_check1);
 }
 
 /*
@@ -551,48 +598,45 @@ static void srcu_advance_batches(struct srcu_struct *sp)
  */
 static void srcu_invoke_callbacks(struct srcu_struct *sp)
 {
-	struct rcu_cblist ready_cbs;
-	struct rcu_head *rhp;
+	int i;
+	struct rcu_head *head;
 
-	spin_lock_irq(&sp->queue_lock);
-	if (!rcu_segcblist_ready_cbs(&sp->srcu_cblist)) {
-		spin_unlock_irq(&sp->queue_lock);
-		return;
-	}
-	rcu_cblist_init(&ready_cbs);
-	rcu_segcblist_extract_done_cbs(&sp->srcu_cblist, &ready_cbs);
-	spin_unlock_irq(&sp->queue_lock);
-	rhp = rcu_cblist_dequeue(&ready_cbs);
-	for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
+	for (i = 0; i < SRCU_CALLBACK_BATCH; i++) {
+		head = rcu_batch_dequeue(&sp->batch_done);
+		if (!head)
+			break;
 		local_bh_disable();
-		rhp->func(rhp);
+		head->func(head);
 		local_bh_enable();
 	}
-	spin_lock_irq(&sp->queue_lock);
-	rcu_segcblist_insert_count(&sp->srcu_cblist, &ready_cbs);
-	spin_unlock_irq(&sp->queue_lock);
 }
 
 /*
  * Finished one round of SRCU grace period.  Start another if there are
  * more SRCU callbacks queued, otherwise put SRCU into not-running state.
  */
-static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
+static void srcu_reschedule(struct srcu_struct *sp)
 {
 	bool pending = true;
-	int state;
 
-	if (rcu_segcblist_empty(&sp->srcu_cblist)) {
+	if (rcu_batch_empty(&sp->batch_done) &&
+	    rcu_batch_empty(&sp->batch_check1) &&
+	    rcu_batch_empty(&sp->batch_check0) &&
+	    rcu_batch_empty(&sp->batch_queue)) {
 		spin_lock_irq(&sp->queue_lock);
-		state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
-		if (rcu_segcblist_empty(&sp->srcu_cblist) &&
-		    state == SRCU_STATE_IDLE)
+		if (rcu_batch_empty(&sp->batch_done) &&
+		    rcu_batch_empty(&sp->batch_check1) &&
+		    rcu_batch_empty(&sp->batch_check0) &&
+		    rcu_batch_empty(&sp->batch_queue)) {
+			sp->running = false;
 			pending = false;
+		}
 		spin_unlock_irq(&sp->queue_lock);
 	}
 
 	if (pending)
-		queue_delayed_work(system_power_efficient_wq, &sp->work, delay);
+		queue_delayed_work(system_power_efficient_wq,
+				   &sp->work, SRCU_INTERVAL);
 }
 
 /*
@@ -604,8 +648,9 @@ void process_srcu(struct work_struct *work)
 
 	sp = container_of(work, struct srcu_struct, work.work);
 
-	srcu_advance_batches(sp);
+	srcu_collect_new(sp);
+	srcu_advance_batches(sp, 1);
 	srcu_invoke_callbacks(sp);
-	srcu_reschedule(sp, atomic_read(&sp->srcu_exp_cnt) ? 0 : SRCU_INTERVAL);
+	srcu_reschedule(sp);
 }
 EXPORT_SYMBOL_GPL(process_srcu);
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
new file mode 100644
index 000000000000..da676b0d016b
--- /dev/null
+++ b/kernel/rcu/srcutree.c
@@ -0,0 +1,613 @@
+/*
+ * Sleepable Read-Copy Update mechanism for mutual exclusion.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright (C) IBM Corporation, 2006
+ * Copyright (C) Fujitsu, 2012
+ *
+ * Author: Paul McKenney <paulmck@us.ibm.com>
+ *	   Lai Jiangshan <laijs@cn.fujitsu.com>
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ *		Documentation/RCU/ *.txt
+ *
+ */
+
+#include <linux/export.h>
+#include <linux/mutex.h>
+#include <linux/percpu.h>
+#include <linux/preempt.h>
+#include <linux/rcupdate_wait.h>
+#include <linux/sched.h>
+#include <linux/smp.h>
+#include <linux/delay.h>
+#include <linux/srcu.h>
+
+#include <linux/rcu_node_tree.h>
+#include "rcu.h"
+
+static int init_srcu_struct_fields(struct srcu_struct *sp)
+{
+	sp->completed = 0;
+	sp->srcu_gp_seq = 0;
+	atomic_set(&sp->srcu_exp_cnt, 0);
+	spin_lock_init(&sp->queue_lock);
+	rcu_segcblist_init(&sp->srcu_cblist);
+	INIT_DELAYED_WORK(&sp->work, process_srcu);
+	sp->per_cpu_ref = alloc_percpu(struct srcu_array);
+	return sp->per_cpu_ref ? 0 : -ENOMEM;
+}
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+
+int __init_srcu_struct(struct srcu_struct *sp, const char *name,
+		       struct lock_class_key *key)
+{
+	/* Don't re-initialize a lock while it is held. */
+	debug_check_no_locks_freed((void *)sp, sizeof(*sp));
+	lockdep_init_map(&sp->dep_map, name, key, 0);
+	return init_srcu_struct_fields(sp);
+}
+EXPORT_SYMBOL_GPL(__init_srcu_struct);
+
+#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+/**
+ * init_srcu_struct - initialize a sleep-RCU structure
+ * @sp: structure to initialize.
+ *
+ * Must invoke this on a given srcu_struct before passing that srcu_struct
+ * to any other function.  Each srcu_struct represents a separate domain
+ * of SRCU protection.
+ */
+int init_srcu_struct(struct srcu_struct *sp)
+{
+	return init_srcu_struct_fields(sp);
+}
+EXPORT_SYMBOL_GPL(init_srcu_struct);
+
+#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+/*
+ * Returns approximate total of the readers' ->lock_count[] values for the
+ * rank of per-CPU counters specified by idx.
+ */
+static unsigned long srcu_readers_lock_idx(struct srcu_struct *sp, int idx)
+{
+	int cpu;
+	unsigned long sum = 0;
+
+	for_each_possible_cpu(cpu) {
+		struct srcu_array *cpuc = per_cpu_ptr(sp->per_cpu_ref, cpu);
+
+		sum += READ_ONCE(cpuc->lock_count[idx]);
+	}
+	return sum;
+}
+
+/*
+ * Returns approximate total of the readers' ->unlock_count[] values for the
+ * rank of per-CPU counters specified by idx.
+ */
+static unsigned long srcu_readers_unlock_idx(struct srcu_struct *sp, int idx)
+{
+	int cpu;
+	unsigned long sum = 0;
+
+	for_each_possible_cpu(cpu) {
+		struct srcu_array *cpuc = per_cpu_ptr(sp->per_cpu_ref, cpu);
+
+		sum += READ_ONCE(cpuc->unlock_count[idx]);
+	}
+	return sum;
+}
+
+/*
+ * Return true if the number of pre-existing readers is determined to
+ * be zero.
+ */
+static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx)
+{
+	unsigned long unlocks;
+
+	unlocks = srcu_readers_unlock_idx(sp, idx);
+
+	/*
+	 * Make sure that a lock is always counted if the corresponding
+	 * unlock is counted. Needs to be a smp_mb() as the read side may
+	 * contain a read from a variable that is written to before the
+	 * synchronize_srcu() in the write side. In this case smp_mb()s
+	 * A and B act like the store buffering pattern.
+	 *
+	 * This smp_mb() also pairs with smp_mb() C to prevent accesses
+	 * after the synchronize_srcu() from being executed before the
+	 * grace period ends.
+	 */
+	smp_mb(); /* A */
+
+	/*
+	 * If the locks are the same as the unlocks, then there must have
+	 * been no readers on this index at some time in between. This does
+	 * not mean that there are no more readers, as one could have read
+	 * the current index but not have incremented the lock counter yet.
+	 *
+	 * Possible bug: There is no guarantee that there haven't been
+	 * ULONG_MAX increments of ->lock_count[] since the unlocks were
+	 * counted, meaning that this could return true even if there are
+	 * still active readers.  Since there are no memory barriers around
+	 * srcu_flip(), the CPU is not required to increment ->completed
+	 * before running srcu_readers_unlock_idx(), which means that there
+	 * could be an arbitrarily large number of critical sections that
+	 * execute after srcu_readers_unlock_idx() but use the old value
+	 * of ->completed.
+	 */
+	return srcu_readers_lock_idx(sp, idx) == unlocks;
+}
+
+/**
+ * srcu_readers_active - returns true if there are readers. and false
+ *                       otherwise
+ * @sp: which srcu_struct to count active readers (holding srcu_read_lock).
+ *
+ * Note that this is not an atomic primitive, and can therefore suffer
+ * severe errors when invoked on an active srcu_struct.  That said, it
+ * can be useful as an error check at cleanup time.
+ */
+static bool srcu_readers_active(struct srcu_struct *sp)
+{
+	int cpu;
+	unsigned long sum = 0;
+
+	for_each_possible_cpu(cpu) {
+		struct srcu_array *cpuc = per_cpu_ptr(sp->per_cpu_ref, cpu);
+
+		sum += READ_ONCE(cpuc->lock_count[0]);
+		sum += READ_ONCE(cpuc->lock_count[1]);
+		sum -= READ_ONCE(cpuc->unlock_count[0]);
+		sum -= READ_ONCE(cpuc->unlock_count[1]);
+	}
+	return sum;
+}
+
+#define SRCU_INTERVAL		1
+
+/**
+ * cleanup_srcu_struct - deconstruct a sleep-RCU structure
+ * @sp: structure to clean up.
+ *
+ * Must invoke this after you are finished using a given srcu_struct that
+ * was initialized via init_srcu_struct(), else you leak memory.
+ */
+void cleanup_srcu_struct(struct srcu_struct *sp)
+{
+	WARN_ON_ONCE(atomic_read(&sp->srcu_exp_cnt));
+	if (WARN_ON(srcu_readers_active(sp)))
+		return; /* Leakage unless caller handles error. */
+	if (WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist)))
+		return; /* Leakage unless caller handles error. */
+	flush_delayed_work(&sp->work);
+	if (WARN_ON(rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) != SRCU_STATE_IDLE)) {
+		pr_info("cleanup_srcu_struct: Active srcu_struct %lu CBs %c state: %d\n", rcu_segcblist_n_cbs(&sp->srcu_cblist), ".E"[rcu_segcblist_empty(&sp->srcu_cblist)], rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)));
+		return; /* Caller forgot to stop doing call_srcu()? */
+	}
+	free_percpu(sp->per_cpu_ref);
+	sp->per_cpu_ref = NULL;
+}
+EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
+
+/*
+ * Counts the new reader in the appropriate per-CPU element of the
+ * srcu_struct.  Must be called from process context.
+ * Returns an index that must be passed to the matching srcu_read_unlock().
+ */
+int __srcu_read_lock(struct srcu_struct *sp)
+{
+	int idx;
+
+	idx = READ_ONCE(sp->completed) & 0x1;
+	__this_cpu_inc(sp->per_cpu_ref->lock_count[idx]);
+	smp_mb(); /* B */  /* Avoid leaking the critical section. */
+	return idx;
+}
+EXPORT_SYMBOL_GPL(__srcu_read_lock);
+
+/*
+ * Removes the count for the old reader from the appropriate per-CPU
+ * element of the srcu_struct.  Note that this may well be a different
+ * CPU than that which was incremented by the corresponding srcu_read_lock().
+ * Must be called from process context.
+ */
+void __srcu_read_unlock(struct srcu_struct *sp, int idx)
+{
+	smp_mb(); /* C */  /* Avoid leaking the critical section. */
+	this_cpu_inc(sp->per_cpu_ref->unlock_count[idx]);
+}
+EXPORT_SYMBOL_GPL(__srcu_read_unlock);
+
+/*
+ * We use an adaptive strategy for synchronize_srcu() and especially for
+ * synchronize_srcu_expedited().  We spin for a fixed time period
+ * (defined below) to allow SRCU readers to exit their read-side critical
+ * sections.  If there are still some readers after a few microseconds,
+ * we repeatedly block for 1-millisecond time periods.
+ */
+#define SRCU_RETRY_CHECK_DELAY		5
+
+/*
+ * Start an SRCU grace period.
+ */
+static void srcu_gp_start(struct srcu_struct *sp)
+{
+	int state;
+
+	rcu_segcblist_accelerate(&sp->srcu_cblist,
+				 rcu_seq_snap(&sp->srcu_gp_seq));
+	rcu_seq_start(&sp->srcu_gp_seq);
+	state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
+	WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
+}
+
+/*
+ * Wait until all readers counted by array index idx complete, but
+ * loop an additional time if there is an expedited grace period pending.
+ * The caller must ensure that ->completed is not changed while checking.
+ */
+static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
+{
+	for (;;) {
+		if (srcu_readers_active_idx_check(sp, idx))
+			return true;
+		if (--trycount + !!atomic_read(&sp->srcu_exp_cnt) <= 0)
+			return false;
+		udelay(SRCU_RETRY_CHECK_DELAY);
+	}
+}
+
+/*
+ * Increment the ->completed counter so that future SRCU readers will
+ * use the other rank of the ->(un)lock_count[] arrays.  This allows
+ * us to wait for pre-existing readers in a starvation-free manner.
+ */
+static void srcu_flip(struct srcu_struct *sp)
+{
+	WRITE_ONCE(sp->completed, sp->completed + 1);
+
+	/*
+	 * Ensure that if the updater misses an __srcu_read_unlock()
+	 * increment, that task's next __srcu_read_lock() will see the
+	 * above counter update.  Note that both this memory barrier
+	 * and the one in srcu_readers_active_idx_check() provide the
+	 * guarantee for __srcu_read_lock().
+	 */
+	smp_mb(); /* D */  /* Pairs with C. */
+}
+
+/*
+ * End an SRCU grace period.
+ */
+static void srcu_gp_end(struct srcu_struct *sp)
+{
+	rcu_seq_end(&sp->srcu_gp_seq);
+
+	spin_lock_irq(&sp->queue_lock);
+	rcu_segcblist_advance(&sp->srcu_cblist,
+			      rcu_seq_current(&sp->srcu_gp_seq));
+	spin_unlock_irq(&sp->queue_lock);
+}
+
+/*
+ * Enqueue an SRCU callback on the specified srcu_struct structure,
+ * initiating grace-period processing if it is not already running.
+ *
+ * Note that all CPUs must agree that the grace period extended beyond
+ * all pre-existing SRCU read-side critical section.  On systems with
+ * more than one CPU, this means that when "func()" is invoked, each CPU
+ * is guaranteed to have executed a full memory barrier since the end of
+ * its last corresponding SRCU read-side critical section whose beginning
+ * preceded the call to call_rcu().  It also means that each CPU executing
+ * an SRCU read-side critical section that continues beyond the start of
+ * "func()" must have executed a memory barrier after the call_rcu()
+ * but before the beginning of that SRCU read-side critical section.
+ * Note that these guarantees include CPUs that are offline, idle, or
+ * executing in user mode, as well as CPUs that are executing in the kernel.
+ *
+ * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
+ * resulting SRCU callback function "func()", then both CPU A and CPU
+ * B are guaranteed to execute a full memory barrier during the time
+ * interval between the call to call_rcu() and the invocation of "func()".
+ * This guarantee applies even if CPU A and CPU B are the same CPU (but
+ * again only if the system has more than one CPU).
+ *
+ * Of course, these guarantees apply only for invocations of call_srcu(),
+ * srcu_read_lock(), and srcu_read_unlock() that are all passed the same
+ * srcu_struct structure.
+ */
+void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
+	       rcu_callback_t func)
+{
+	unsigned long flags;
+
+	head->next = NULL;
+	head->func = func;
+	spin_lock_irqsave(&sp->queue_lock, flags);
+	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
+	rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
+	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
+		srcu_gp_start(sp);
+		queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
+	}
+	spin_unlock_irqrestore(&sp->queue_lock, flags);
+}
+EXPORT_SYMBOL_GPL(call_srcu);
+
+static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay);
+
+/*
+ * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
+ */
+static void __synchronize_srcu(struct srcu_struct *sp)
+{
+	struct rcu_synchronize rcu;
+	struct rcu_head *head = &rcu.head;
+
+	RCU_LOCKDEP_WARN(lock_is_held(&sp->dep_map) ||
+			 lock_is_held(&rcu_bh_lock_map) ||
+			 lock_is_held(&rcu_lock_map) ||
+			 lock_is_held(&rcu_sched_lock_map),
+			 "Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");
+
+	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
+		return;
+	might_sleep();
+	init_completion(&rcu.completion);
+
+	head->next = NULL;
+	head->func = wakeme_after_rcu;
+	spin_lock_irq(&sp->queue_lock);
+	smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
+	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
+		/* steal the processing owner */
+		rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
+		srcu_gp_start(sp);
+		spin_unlock_irq(&sp->queue_lock);
+		/* give the processing owner to work_struct */
+		srcu_reschedule(sp, 0);
+	} else {
+		rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
+		spin_unlock_irq(&sp->queue_lock);
+	}
+
+	wait_for_completion(&rcu.completion);
+	smp_mb(); /* Caller's later accesses after GP. */
+}
+
+/**
+ * synchronize_srcu_expedited - Brute-force SRCU grace period
+ * @sp: srcu_struct with which to synchronize.
+ *
+ * Wait for an SRCU grace period to elapse, but be more aggressive about
+ * spinning rather than blocking when waiting.
+ *
+ * Note that synchronize_srcu_expedited() has the same deadlock and
+ * memory-ordering properties as does synchronize_srcu().
+ */
+void synchronize_srcu_expedited(struct srcu_struct *sp)
+{
+	bool do_norm = rcu_gp_is_normal();
+
+	if (!do_norm) {
+		atomic_inc(&sp->srcu_exp_cnt);
+		smp_mb__after_atomic(); /* increment before GP. */
+	}
+	__synchronize_srcu(sp);
+	if (!do_norm) {
+		smp_mb__before_atomic(); /* GP before decrement. */
+		atomic_dec(&sp->srcu_exp_cnt);
+	}
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
+
+/**
+ * synchronize_srcu - wait for prior SRCU read-side critical-section completion
+ * @sp: srcu_struct with which to synchronize.
+ *
+ * Wait for the count to drain to zero of both indexes. To avoid the
+ * possible starvation of synchronize_srcu(), it waits for the count of
+ * the index=((->completed & 1) ^ 1) to drain to zero at first,
+ * and then flip the completed and wait for the count of the other index.
+ *
+ * Can block; must be called from process context.
+ *
+ * Note that it is illegal to call synchronize_srcu() from the corresponding
+ * SRCU read-side critical section; doing so will result in deadlock.
+ * However, it is perfectly legal to call synchronize_srcu() on one
+ * srcu_struct from some other srcu_struct's read-side critical section,
+ * as long as the resulting graph of srcu_structs is acyclic.
+ *
+ * There are memory-ordering constraints implied by synchronize_srcu().
+ * On systems with more than one CPU, when synchronize_srcu() returns,
+ * each CPU is guaranteed to have executed a full memory barrier since
+ * the end of its last corresponding SRCU-sched read-side critical section
+ * whose beginning preceded the call to synchronize_srcu().  In addition,
+ * each CPU having an SRCU read-side critical section that extends beyond
+ * the return from synchronize_srcu() is guaranteed to have executed a
+ * full memory barrier after the beginning of synchronize_srcu() and before
+ * the beginning of that SRCU read-side critical section.  Note that these
+ * guarantees include CPUs that are offline, idle, or executing in user mode,
+ * as well as CPUs that are executing in the kernel.
+ *
+ * Furthermore, if CPU A invoked synchronize_srcu(), which returned
+ * to its caller on CPU B, then both CPU A and CPU B are guaranteed
+ * to have executed a full memory barrier during the execution of
+ * synchronize_srcu().  This guarantee applies even if CPU A and CPU B
+ * are the same CPU, but again only if the system has more than one CPU.
+ *
+ * Of course, these memory-ordering guarantees apply only when
+ * synchronize_srcu(), srcu_read_lock(), and srcu_read_unlock() are
+ * passed the same srcu_struct structure.
+ */
+void synchronize_srcu(struct srcu_struct *sp)
+{
+	if (rcu_gp_is_expedited())
+		synchronize_srcu_expedited(sp);
+	else
+		__synchronize_srcu(sp);
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu);
+
+/**
+ * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
+ * @sp: srcu_struct on which to wait for in-flight callbacks.
+ */
+void srcu_barrier(struct srcu_struct *sp)
+{
+	synchronize_srcu(sp);
+}
+EXPORT_SYMBOL_GPL(srcu_barrier);
+
+/**
+ * srcu_batches_completed - return batches completed.
+ * @sp: srcu_struct on which to report batch completion.
+ *
+ * Report the number of batches, correlated with, but not necessarily
+ * precisely the same as, the number of grace periods that have elapsed.
+ */
+unsigned long srcu_batches_completed(struct srcu_struct *sp)
+{
+	return sp->completed;
+}
+EXPORT_SYMBOL_GPL(srcu_batches_completed);
+
+/*
+ * Core SRCU state machine.  Advance callbacks from ->batch_check0 to
+ * ->batch_check1 and then to ->batch_done as readers drain.
+ */
+static void srcu_advance_batches(struct srcu_struct *sp)
+{
+	int idx;
+
+	/*
+	 * Because readers might be delayed for an extended period after
+	 * fetching ->completed for their index, at any point in time there
+	 * might well be readers using both idx=0 and idx=1.  We therefore
+	 * need to wait for readers to clear from both index values before
+	 * invoking a callback.
+	 *
+	 * The load-acquire ensures that we see the accesses performed
+	 * by the prior grace period.
+	 */
+	idx = rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq)); /* ^^^ */
+	if (idx == SRCU_STATE_IDLE) {
+		spin_lock_irq(&sp->queue_lock);
+		if (rcu_segcblist_empty(&sp->srcu_cblist)) {
+			spin_unlock_irq(&sp->queue_lock);
+			return;
+		}
+		idx = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
+		if (idx == SRCU_STATE_IDLE)
+			srcu_gp_start(sp);
+		spin_unlock_irq(&sp->queue_lock);
+		if (idx != SRCU_STATE_IDLE)
+			return; /* Someone else started the grace period. */
+	}
+
+	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
+		idx = 1 ^ (sp->completed & 1);
+		if (!try_check_zero(sp, idx, 1))
+			return; /* readers present, retry later. */
+		srcu_flip(sp);
+		rcu_seq_set_state(&sp->srcu_gp_seq, SRCU_STATE_SCAN2);
+	}
+
+	if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN2) {
+
+		/*
+		 * SRCU read-side critical sections are normally short,
+		 * so check at least twice in quick succession after a flip.
+		 */
+		idx = 1 ^ (sp->completed & 1);
+		if (!try_check_zero(sp, idx, 2))
+			return; /* readers present, retry after later. */
+		srcu_gp_end(sp);
+	}
+}
+
+/*
+ * Invoke a limited number of SRCU callbacks that have passed through
+ * their grace period.  If there are more to do, SRCU will reschedule
+ * the workqueue.  Note that needed memory barriers have been executed
+ * in this task's context by srcu_readers_active_idx_check().
+ */
+static void srcu_invoke_callbacks(struct srcu_struct *sp)
+{
+	struct rcu_cblist ready_cbs;
+	struct rcu_head *rhp;
+
+	spin_lock_irq(&sp->queue_lock);
+	if (!rcu_segcblist_ready_cbs(&sp->srcu_cblist)) {
+		spin_unlock_irq(&sp->queue_lock);
+		return;
+	}
+	rcu_cblist_init(&ready_cbs);
+	rcu_segcblist_extract_done_cbs(&sp->srcu_cblist, &ready_cbs);
+	spin_unlock_irq(&sp->queue_lock);
+	rhp = rcu_cblist_dequeue(&ready_cbs);
+	for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
+		local_bh_disable();
+		rhp->func(rhp);
+		local_bh_enable();
+	}
+	spin_lock_irq(&sp->queue_lock);
+	rcu_segcblist_insert_count(&sp->srcu_cblist, &ready_cbs);
+	spin_unlock_irq(&sp->queue_lock);
+}
+
+/*
+ * Finished one round of SRCU grace period.  Start another if there are
+ * more SRCU callbacks queued, otherwise put SRCU into not-running state.
+ */
+static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
+{
+	bool pending = true;
+	int state;
+
+	if (rcu_segcblist_empty(&sp->srcu_cblist)) {
+		spin_lock_irq(&sp->queue_lock);
+		state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
+		if (rcu_segcblist_empty(&sp->srcu_cblist) &&
+		    state == SRCU_STATE_IDLE)
+			pending = false;
+		spin_unlock_irq(&sp->queue_lock);
+	}
+
+	if (pending)
+		queue_delayed_work(system_power_efficient_wq, &sp->work, delay);
+}
+
+/*
+ * This is the work-queue function that handles SRCU grace periods.
+ */
+void process_srcu(struct work_struct *work)
+{
+	struct srcu_struct *sp;
+
+	sp = container_of(work, struct srcu_struct, work.work);
+
+	srcu_advance_batches(sp);
+	srcu_invoke_callbacks(sp);
+	srcu_reschedule(sp, atomic_read(&sp->srcu_exp_cnt) ? 0 : SRCU_INTERVAL);
+}
+EXPORT_SYMBOL_GPL(process_srcu);
-- 
2.5.2

^ permalink raw reply	[flat|nested] 176+ messages in thread

* [PATCH v2 tip/core/rcu 38/39] srcu: Parallelize callback handling
  2017-04-17 23:44 ` [PATCH v2 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
                     ` (36 preceding siblings ...)
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 37/39] srcu: Introduce CLASSIC_SRCU Kconfig option Paul E. McKenney
@ 2017-04-17 23:45   ` Paul E. McKenney
  2017-04-17 23:45   ` [PATCH v2 tip/core/rcu 39/39] rcu: Make non-preemptive schedule be Tasks RCU quiescent state Paul E. McKenney
  2017-04-19 16:58   ` [PATCH v3 tip/core/rcu 0/40] SRCU callback parallelization for 4.12 Paul E. McKenney
  39 siblings, 0 replies; 176+ messages in thread
From: Paul E. McKenney @ 2017-04-17 23:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
	tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
	bobby.prani, Paul E. McKenney

Peter Zijlstra proposed using SRCU to reduce mmap_sem contention [1,2],
however, there are workloads that could result in a high volume of
concurrent invocations of call_srcu(), which with current SRCU would
result in excessive lock contention on the srcu_struct structure's
->queue_lock, which protects SRCU's callback lists.  This commit therefore
moves SRCU to per-CPU callback lists, thus greatly reducing contention.

Because a given SRCU instance no longer has a single centralized callback
list, starting grace periods and invoking callbacks are both more complex
than in the single-list Classic SRCU implementation.  Starting grace
periods and handling callbacks are now handled using an srcu_node tree
that is in some ways similar to the rcu_node trees used by RCU-bh,
RCU-preempt, and RCU-sched (for example, the srcu_node tree shape is
controlled by exactly the same Kconfig options and boot parameters that
control the shape of the rcu_node tree).

In addition, the old per-CPU srcu_array structure is now named srcu_data
and contains an rcu_segcblist structure named ->srcu_cblist for its
callbacks (and a spinlock to protect this).  The srcu_struct gets
an srcu_gp_seq that is used to associate callback segments with the
corresponding completion-time grace-period number.  These completion-time
grace-period numbers are propagated up the srcu_node tree so that the
grace-period workqueue handler can determine whether additional grace
periods are needed on the one hand and where to look for callbacks that
are ready to be invoked.

The srcu_barrier() function must now wait on all instances of the per-CPU
->srcu_cblist.  Because each ->srcu_cblist is protected by ->lock,
srcu_barrier() can remotely add the needed callbacks.  In theory,
it could also remotely start grace periods, but in practice doing so
is complex and racy.  And interestingly enough, it is never necessary
for srcu_barrier() to start a grace period because srcu_barrier() only
enqueues a callback when a callback is already present--and it turns out
that a grace period has to have already been started for this pre-existing
callback.  Furthermore, it is only the callback that srcu_barrier()
needs to wait on, not any particular grace period.  Therefore, a new
rcu_segcblist_entrain() function enqueues the srcu_barrier() function's
callback into the same segment occupied by the last pre-existing callback
in the list.  The special case where all the pre-existing callbacks are
on a different list (because they are in the process of being invoked)
is handled by enqueuing srcu_barrier()'s callback into the RCU_DONE_TAIL
segment, relying on the done-callbacks check that takes place after all
callbacks are inovked.

Note that the readers use the same algorithm as before.  Note that there
is a separate srcu_idx that tells the readers what counter to increment.
This unfortunately cannot be combined with srcu_gp_seq because they
need to be incremented at different times.

This commit introduces some ugly #ifdefs in rcutorture.  These will go
away when I feel good enough about Tree SRCU to ditch Classic SRCU.

Some crude performance comparisons, courtesy of a quickly hacked rcuperf
asynchronous-grace-period capability:

			Callback Queuing Overhead
			-------------------------
	# CPUS		Classic SRCU	Tree SRCU
	------          ------------    ---------
	     2              0.349 us     0.342 us
	    16             31.66  us     0.4   us
	    41             ---------     0.417 us

The times are the 90th percentiles, a statistic that was chosen to reject
the overheads of the occasional srcu_barrier() call needed to avoid OOMing
the test machine.  The rcuperf test hangs when running Classic SRCU at 41
CPUs, hence the line of dashes.  Despite the hacks to both the rcuperf code
and that statistics, this is a convincing demonstration of Tree SRCU's
performance and scalability advantages.

[1] https://lwn.net/Articles/309030/
[2] https://patchwork.kernel.org/patch/5108281/

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcu_segcblist.h |  42 ++-
 include/linux/srcutree.h      |  80 ++++--
 kernel/rcu/rcutorture.c       |  20 +-
 kernel/rcu/srcutree.c         | 639 +++++++++++++++++++++++++++++++++---------
 kernel/rcu/tree.c             |   6 +
 kernel/rcu/tree.h             |   8 +
 6 files changed, 645 insertions(+), 150 deletions(-)

diff --git a/include/linux/rcu_segcblist.h b/include/linux/rcu_segcblist.h
index 74b1e7243955..ced8f313fd05 100644
--- a/include/linux/rcu_segcblist.h
+++ b/include/linux/rcu_segcblist.h
@@ -402,6 +402,37 @@ static inline void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
 }
 
 /*
+ * Entrain the specified callback onto the specified rcu_segcblist at
+ * the end of the last non-empty segment.  If the entire rcu_segcblist
+ * is empty, make no change, but return false.
+ *
+ * This is intended for use by rcu_barrier()-like primitives, -not-
+ * for normal grace-period use.  IMPORTANT:  The callback you enqueue
+ * will wait for all prior callbacks, NOT necessarily for a grace
+ * period.  You have been warned.
+ */
+static inline bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp,
+					 struct rcu_head *rhp, bool lazy)
+{
+	int i;
+
+	if (rcu_segcblist_n_cbs(rsclp) == 0)
+		return false;
+	WRITE_ONCE(rsclp->len, rsclp->len + 1);
+	if (lazy)
+		rsclp->len_lazy++;
+	smp_mb(); /* Ensure counts are updated before callback is entrained. */
+	rhp->next = NULL;
+	for (i = RCU_NEXT_TAIL; i > RCU_DONE_TAIL; i--)
+		if (rsclp->tails[i] != rsclp->tails[i - 1])
+			break;
+	*rsclp->tails[i] = rhp;
+	for (; i <= RCU_NEXT_TAIL; i++)
+		rsclp->tails[i] = &rhp->next;
+	return true;
+}
+
+/*
  * Extract only the counts from the specified rcu_segcblist structure,
  * and place them in the specified rcu_cblist structure.  This function
  * supports both callback orphaning and invocation, hence the separation
@@ -537,7 +568,8 @@ static inline void rcu_segcblist_advance(struct rcu_segcblist *rsclp,
 	int i, j;
 
 	WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
-	WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL));
+	if (rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL))
+		return;
 
 	/*
 	 * Find all callbacks whose ->gp_seq numbers indicate that they
@@ -582,8 +614,9 @@ static inline void rcu_segcblist_advance(struct rcu_segcblist *rsclp,
  * them to complete at the end of the earlier grace period.
  *
  * This function operates on an rcu_segcblist structure, and also the
- * grace-period sequence number at which new callbacks would become
- * ready to invoke.
+ * grace-period sequence number seq at which new callbacks would become
+ * ready to invoke.  Returns true if there are callbacks that won't be
+ * ready to invoke until seq, false otherwise.
  */
 static inline bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp,
 					    unsigned long seq)
@@ -591,7 +624,8 @@ static inline bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp,
 	int i;
 
 	WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
-	WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL));
+	if (rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL))
+		return false;
 
 	/*
 	 * Find the segment preceding the oldest segment of callbacks
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index f2b3bd6c6bc2..0400e211aa44 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -24,25 +24,75 @@
 #ifndef _LINUX_SRCU_TREE_H
 #define _LINUX_SRCU_TREE_H
 
-struct srcu_array {
-	unsigned long lock_count[2];
-	unsigned long unlock_count[2];
+#include <linux/rcu_node_tree.h>
+#include <linux/completion.h>
+
+struct srcu_node;
+struct srcu_struct;
+
+/*
+ * Per-CPU structure feeding into leaf srcu_node, similar in function
+ * to rcu_node.
+ */
+struct srcu_data {
+	/* Read-side state. */
+	unsigned long srcu_lock_count[2];	/* Locks per CPU. */
+	unsigned long srcu_unlock_count[2];	/* Unlocks per CPU. */
+
+	/* Update-side state. */
+	spinlock_t lock ____cacheline_internodealigned_in_smp;
+	struct rcu_segcblist srcu_cblist;	/* List of callbacks.*/
+	unsigned long srcu_gp_seq_needed;	/* Furthest future GP needed. */
+	bool srcu_cblist_invoking;		/* Invoking these CBs? */
+	struct delayed_work work;		/* Context for CB invoking. */
+	struct rcu_head srcu_barrier_head;	/* For srcu_barrier() use. */
+	struct srcu_node *mynode;		/* Leaf srcu_node. */
+	int cpu;
+	struct srcu_struct *sp;
 };
 
+/*
+ * Node in SRCU combining tree, similar in function to rcu_data.
+ */
+struct srcu_node {
+	spinlock_t lock;
+	unsigned long srcu_have_cbs[4];		/* GP seq for children */
+						/*  having CBs, but only */
+						/*  is > ->srcu_gq_seq. */
+	struct srcu_node *srcu_parent;		/* Next up in tree. */
+	int grplo;				/* Least CPU for node. */
+	int grphi;				/* Biggest CPU for node. */
+};
+
+/*
+ * Per-SRCU-domain structure, similar in function to rcu_state.
+ */
 struct srcu_struct {
-	unsigned long completed;
-	unsigned long srcu_gp_seq;
-	atomic_t srcu_exp_cnt;
-	struct srcu_array __percpu *per_cpu_ref;
-	spinlock_t queue_lock; /* protect ->srcu_cblist */
-	struct rcu_segcblist srcu_cblist;
+	struct srcu_node node[NUM_RCU_NODES];	/* Combining tree. */
+	struct srcu_node *level[RCU_NUM_LVLS + 1];
+						/* First node at each level. */
+	struct mutex srcu_cb_mutex;		/* Serialize CB preparation. */
+	spinlock_t gp_lock;			/* protect ->srcu_cblist */
+	struct mutex srcu_gp_mutex;		/* Serialize GP work. */
+	unsigned int srcu_idx;			/* Current rdr array element. */
+	unsigned long srcu_gp_seq;		/* Grace-period seq #. */
+	unsigned long srcu_gp_seq_needed;	/* Latest gp_seq needed. */
+	atomic_t srcu_exp_cnt;			/* # ongoing expedited GPs. */
+	struct srcu_data __percpu *sda;		/* Per-CPU srcu_data array. */
+	unsigned long srcu_barrier_seq;		/* srcu_barrier seq #. */
+	struct mutex srcu_barrier_mutex;	/* Serialize barrier ops. */
+	struct completion srcu_barrier_completion;
+						/* Awaken barrier rq at end. */
+	atomic_t srcu_barrier_cpu_cnt;		/* # CPUs not yet posting a */
+						/*  callback for the barrier */
+						/*  operation. */
 	struct delayed_work work;
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map dep_map;
 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 };
 
-/* Values for -> state variable. */
+/* Values for state variable (bottom bits of ->srcu_gp_seq). */
 #define SRCU_STATE_IDLE		0
 #define SRCU_STATE_SCAN1	1
 #define SRCU_STATE_SCAN2	2
@@ -51,11 +101,9 @@ void process_srcu(struct work_struct *work);
 
 #define __SRCU_STRUCT_INIT(name)					\
 	{								\
-		.completed = -300,					\
-		.per_cpu_ref = &name##_srcu_array,			\
-		.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock),	\
-		.srcu_cblist = RCU_SEGCBLIST_INITIALIZER(name.srcu_cblist),\
-		.work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
+		.sda = &name##_srcu_data,				\
+		.gp_lock = __SPIN_LOCK_UNLOCKED(name.gp_lock),		\
+		.srcu_gp_seq_needed = 0 - 1,				\
 		__SRCU_DEP_MAP_INIT(name)				\
 	}
 
@@ -79,7 +127,7 @@ void process_srcu(struct work_struct *work);
  * See include/linux/percpu-defs.h for the rules on per-CPU variables.
  */
 #define __DEFINE_SRCU(name, is_static)					\
-	static DEFINE_PER_CPU(struct srcu_array, name##_srcu_array);\
+	static DEFINE_PER_CPU(struct srcu_data, name##_srcu_data);\
 	is_static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
 #define DEFINE_SRCU(name)		__DEFINE_SRCU(name, /* not static */)
 #define DEFINE_STATIC_SRCU(name)	__DEFINE_SRCU(name, static)
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 6f344b6748a8..e9d4527cdd43 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -563,17 +563,30 @@ static void srcu_torture_stats(void)
 	int idx;
 
 #if defined(CONFIG_TREE_SRCU) || defined(CONFIG_CLASSIC_SRCU)
+#ifdef CONFIG_TREE_SRCU
+	idx = srcu_ctlp->srcu_idx & 0x1;
+#else /* #ifdef CONFIG_TREE_SRCU */
 	idx = srcu_ctlp->completed & 0x1;
+#endif /* #else #ifdef CONFIG_TREE_SRCU */
 	pr_alert("%s%s Tree SRCU per-CPU(idx=%d):",
 		 torture_type, TORTURE_FLAG, idx);
 	for_each_possible_cpu(cpu) {
 		unsigned long l0, l1;
 		unsigned long u0, u1;
 		long c0, c1;
-		struct srcu_array *counts = per_cpu_ptr(srcu_ctlp->per_cpu_ref, cpu);
+#ifdef CONFIG_TREE_SRCU
+		struct srcu_data *counts;
 
+		counts = per_cpu_ptr(srcu_ctlp->sda, cpu);
+		u0 = counts->srcu_unlock_count[!idx];
+		u1 = counts->srcu_unlock_count[idx];
+#else /* #ifdef CONFIG_TREE_SRCU */
+		struct srcu_array *counts;
+
+		counts = per_cpu_ptr(srcu_ctlp->per_cpu_ref, cpu);
 		u0 = counts->unlock_count[!idx];
 		u1 = counts->unlock_count[idx];
+#endif /* #else #ifdef CONFIG_TREE_SRCU */
 
 		/*
 		 * Make sure that a lock is always counted if the corresponding
@@ -581,8 +594,13 @@ static void srcu_torture_stats(void)
 		 */
 		smp_rmb();
 
+#ifdef CONFIG_TREE_SRCU
+		l0 = counts->srcu_lock_count[!idx];
+		l1 = counts->srcu_lock_count[idx];
+#else /* #ifdef CONFIG_TREE_SRCU */
 		l0 = counts->lock_count[!idx];
 		l1 = counts->lock_count[idx];
+#endif /* #else #ifdef CONFIG_TREE_SRCU */
 
 		c0 = l0 - u0;
 		c1 = l1 - u1;
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index da676b0d016b..f9c684d79faa 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -36,19 +36,110 @@
 #include <linux/delay.h>
 #include <linux/srcu.h>
 
-#include <linux/rcu_node_tree.h>
 #include "rcu.h"
 
-static int init_srcu_struct_fields(struct srcu_struct *sp)
+static void srcu_invoke_callbacks(struct work_struct *work);
+static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay);
+
+/*
+ * Initialize SRCU combining tree.  Note that statically allocated
+ * srcu_struct structures might already have srcu_read_lock() and
+ * srcu_read_unlock() running against them.  So if the is_static parameter
+ * is set, don't initialize ->srcu_lock_count[] and ->srcu_unlock_count[].
+ */
+static void init_srcu_struct_nodes(struct srcu_struct *sp, bool is_static)
 {
-	sp->completed = 0;
+	int cpu;
+	int i;
+	int level = 0;
+	int levelspread[RCU_NUM_LVLS];
+	struct srcu_data *sdp;
+	struct srcu_node *snp;
+	struct srcu_node *snp_first;
+
+	/* Work out the overall tree geometry. */
+	sp->level[0] = &sp->node[0];
+	for (i = 1; i < rcu_num_lvls; i++)
+		sp->level[i] = sp->level[i - 1] + num_rcu_lvl[i - 1];
+	rcu_init_levelspread(levelspread, num_rcu_lvl);
+
+	/* Each pass through this loop initializes one srcu_node structure. */
+	rcu_for_each_node_breadth_first(sp, snp) {
+		spin_lock_init(&snp->lock);
+		for (i = 0; i < ARRAY_SIZE(snp->srcu_have_cbs); i++)
+			snp->srcu_have_cbs[i] = 0;
+		snp->grplo = -1;
+		snp->grphi = -1;
+		if (snp == &sp->node[0]) {
+			/* Root node, special case. */
+			snp->srcu_parent = NULL;
+			continue;
+		}
+
+		/* Non-root node. */
+		if (snp == sp->level[level + 1])
+			level++;
+		snp->srcu_parent = sp->level[level - 1] +
+				   (snp - sp->level[level]) /
+				   levelspread[level - 1];
+	}
+
+	/*
+	 * Initialize the per-CPU srcu_data array, which feeds into the
+	 * leaves of the srcu_node tree.
+	 */
+	WARN_ON_ONCE(ARRAY_SIZE(sdp->srcu_lock_count) !=
+		     ARRAY_SIZE(sdp->srcu_unlock_count));
+	level = rcu_num_lvls - 1;
+	snp_first = s