[PATCH tip/core/rcu 0/16] Miscellaneous fixes for 4.3

[PATCH tip/core/rcu 0/16] Miscellaneous fixes for 4.3

[Paul E. McKenney]

Hello!

This series contains miscellaneous fixes.

1.	Drop RCU_USER_QS in favor of NO_HZ_FULL.

2.	Deinline rcu_read_lock_sched_held() even in kernels built with
	CONFIG_DEBUG_LOCK_ALLOC=y, courtesy of Denys Vlasenko.

3.	Change srcu_readers_active()'s return type to bool, courtesy
	of Nicholas Mc Guire.

4.	Add RCU-sched flavors get-state/cond-sync functions, namely
	get_state_synchronize_sched() and cond_synchronize_sched().

5.	Hide RCU_NOCB_CPU behind RCU_EXPERT, arriving at fully
	automated Kconfig setup for RCU.

6.	Use WRITE_ONCE in RCU_INIT_POINTER, courtesy of Peter Zijlstra.

7.	Fix obsolete priority-boosting comment.

8.	Create a synchronize_rcu_mult() to allow overlapped synchronous
	grace periods.

9.	Use synchronize_rcu_mult() to make _cpu_down() wait for its
	RCU and RCU-sched grace periods concurrently.

10.	Make rcu_is_watching() really be notrace, courtesy of =
	Alexei Starovoitov.

11.	Rename rcu_lockdep_assert() to RCU_LOCKDEP_WARN().

12.	Fix backwards RCU_LOCKDEP_WARN() in synchronize_rcu_tasks().

13.	Clarify CONFIG_RCU_EQS_DEBUG help text.

14.	Update RCU MAINTAINERS email address, courtesy of Lai Jiangshan.

15.	Make checkpatch.pl warn on expedited RCU grace periods.

16.	Don't disable CPU hotplug during OOM notifiers.

							Thanx, Paul

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

 b/Documentation/RCU/whatisRCU.txt  |    2 
 b/MAINTAINERS                      |    6 -
 b/arch/x86/kernel/cpu/mcheck/mce.c |    6 -
 b/arch/x86/kernel/traps.c          |    2 
 b/drivers/base/power/opp.c         |    4 -
 b/include/linux/fdtable.h          |    4 -
 b/include/linux/rcupdate.h         |  144 ++++++++++++++++++++-----------------
 b/include/linux/rcutiny.h          |   10 ++
 b/include/linux/rcutree.h          |    2 
 b/include/linux/types.h            |    3 
 b/init/Kconfig                     |   10 --
 b/kernel/cgroup.c                  |    4 -
 b/kernel/cpu.c                     |   10 +-
 b/kernel/pid.c                     |    5 -
 b/kernel/rcu/rcutorture.c          |    2 
 b/kernel/rcu/srcu.c                |   15 ++-
 b/kernel/rcu/tiny.c                |    8 +-
 b/kernel/rcu/tree.c                |   92 ++++++++++++++++++-----
 b/kernel/rcu/tree_plugin.h         |   13 +--
 b/kernel/rcu/update.c              |   92 ++++++++++++++++++++---
 b/kernel/sched/core.c              |    8 +-
 b/kernel/time/Kconfig              |    2 
 b/kernel/workqueue.c               |   20 ++---
 b/lib/Kconfig.debug                |    2 
 b/scripts/checkpatch.pl            |   19 ++++
 b/security/device_cgroup.c         |    6 -
 26 files changed, 322 insertions(+), 169 deletions(-)

[PATCH tip/core/rcu 01/16] rcu: Drop RCU_USER_QS in favor of NO_HZ_FULL

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

The RCU_USER_QS Kconfig parameter is now just a synonym for NO_HZ_FULL,
so this commit eliminates RCU_USER_QS, replacing all uses with NO_HZ_FULL.

Reported-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
---
 include/linux/rcupdate.h | 4 ++--
 init/Kconfig             | 9 ---------
 kernel/rcu/tree.c        | 8 ++++----
 kernel/time/Kconfig      | 2 --
 4 files changed, 6 insertions(+), 17 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 4cf5f51b4c9c..237f7b8d38ba 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -309,7 +309,7 @@ static inline void rcu_sysrq_end(void)
 }
 #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
 
-#ifdef CONFIG_RCU_USER_QS
+#ifdef CONFIG_NO_HZ_FULL
 void rcu_user_enter(void);
 void rcu_user_exit(void);
 #else
@@ -317,7 +317,7 @@ static inline void rcu_user_enter(void) { }
 static inline void rcu_user_exit(void) { }
 static inline void rcu_user_hooks_switch(struct task_struct *prev,
 					 struct task_struct *next) { }
-#endif /* CONFIG_RCU_USER_QS */
+#endif /* CONFIG_NO_HZ_FULL */
 
 #ifdef CONFIG_RCU_NOCB_CPU
 void rcu_init_nohz(void);
diff --git a/init/Kconfig b/init/Kconfig
index af09b4fb43d2..fdeff4ab5995 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -538,15 +538,6 @@ config RCU_STALL_COMMON
 config CONTEXT_TRACKING
        bool
 
-config RCU_USER_QS
-	bool
-	help
-	  This option sets hooks on kernel / userspace boundaries and
-	  puts RCU in extended quiescent state when the CPU runs in
-	  userspace. It means that when a CPU runs in userspace, it is
-	  excluded from the global RCU state machine and thus doesn't
-	  try to keep the timer tick on for RCU.
-
 config CONTEXT_TRACKING_FORCE
 	bool "Force context tracking"
 	depends on CONTEXT_TRACKING
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 65137bc28b2b..8b5dd8ba9495 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -701,7 +701,7 @@ void rcu_idle_enter(void)
 }
 EXPORT_SYMBOL_GPL(rcu_idle_enter);
 
-#ifdef CONFIG_RCU_USER_QS
+#ifdef CONFIG_NO_HZ_FULL
 /**
  * rcu_user_enter - inform RCU that we are resuming userspace.
  *
@@ -714,7 +714,7 @@ void rcu_user_enter(void)
 {
 	rcu_eqs_enter(1);
 }
-#endif /* CONFIG_RCU_USER_QS */
+#endif /* CONFIG_NO_HZ_FULL */
 
 /**
  * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
@@ -828,7 +828,7 @@ void rcu_idle_exit(void)
 }
 EXPORT_SYMBOL_GPL(rcu_idle_exit);
 
-#ifdef CONFIG_RCU_USER_QS
+#ifdef CONFIG_NO_HZ_FULL
 /**
  * rcu_user_exit - inform RCU that we are exiting userspace.
  *
@@ -839,7 +839,7 @@ void rcu_user_exit(void)
 {
 	rcu_eqs_exit(1);
 }
-#endif /* CONFIG_RCU_USER_QS */
+#endif /* CONFIG_NO_HZ_FULL */
 
 /**
  * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 579ce1b929af..4008d9f95dd7 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -92,12 +92,10 @@ config NO_HZ_FULL
 	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
 	# We need at least one periodic CPU for timekeeping
 	depends on SMP
-	# RCU_USER_QS dependency
 	depends on HAVE_CONTEXT_TRACKING
 	# VIRT_CPU_ACCOUNTING_GEN dependency
 	depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
 	select NO_HZ_COMMON
-	select RCU_USER_QS
 	select RCU_NOCB_CPU
 	select VIRT_CPU_ACCOUNTING_GEN
 	select IRQ_WORK
-- 
1.8.1.5

[PATCH tip/core/rcu 02/16] rcu: Deinline rcu_read_lock_sched_held() if DEBUG_LOCK_ALLOC

[Paul E. McKenney]

From: Denys Vlasenko <dvlasenk@redhat.com>

DEBUG_LOCK_ALLOC=y is not a production setting, but it is
not very unusual either. Many developers routinely
use kernels built with it enabled.

Apart from being selected by hand, it is also auto-selected by
PROVE_LOCKING "Lock debugging: prove locking correctness" and
LOCK_STAT "Lock usage statistics" config options.
LOCK STAT is necessary for "perf lock" to work.

I wouldn't spend too much time optimizing it, but this particular
function has a very large cost in code size: when it is deinlined,
code size decreases by 830,000 bytes:

    text     data      bss       dec     hex filename
85674192 22294776 20627456 128596424 7aa39c8 vmlinux.before
84837612 22294424 20627456 127759492 79d7484 vmlinux

(with this config: http://busybox.net/~vda/kernel_config)

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
CC: Josh Triplett <josh@joshtriplett.org>
CC: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Lai Jiangshan <laijs@cn.fujitsu.com>
CC: Tejun Heo <tj@kernel.org>
CC: Oleg Nesterov <oleg@redhat.com>
CC: linux-kernel@vger.kernel.org
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcupdate.h | 40 ++-------------------------------------
 kernel/rcu/update.c      | 49 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 38 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 237f7b8d38ba..def6d45ad61c 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -469,46 +469,10 @@ int rcu_read_lock_bh_held(void);
  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
  * RCU-sched read-side critical section.  In absence of
  * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
- * critical section unless it can prove otherwise.  Note that disabling
- * of preemption (including disabling irqs) counts as an RCU-sched
- * read-side critical section.  This is useful for debug checks in functions
- * that required that they be called within an RCU-sched read-side
- * critical section.
- *
- * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
- * and while lockdep is disabled.
- *
- * Note that if the CPU is in the idle loop from an RCU point of
- * view (ie: that we are in the section between rcu_idle_enter() and
- * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
- * did an rcu_read_lock().  The reason for this is that RCU ignores CPUs
- * that are in such a section, considering these as in extended quiescent
- * state, so such a CPU is effectively never in an RCU read-side critical
- * section regardless of what RCU primitives it invokes.  This state of
- * affairs is required --- we need to keep an RCU-free window in idle
- * where the CPU may possibly enter into low power mode. This way we can
- * notice an extended quiescent state to other CPUs that started a grace
- * period. Otherwise we would delay any grace period as long as we run in
- * the idle task.
- *
- * Similarly, we avoid claiming an SRCU read lock held if the current
- * CPU is offline.
+ * critical section unless it can prove otherwise.
  */
 #ifdef CONFIG_PREEMPT_COUNT
-static inline int rcu_read_lock_sched_held(void)
-{
-	int lockdep_opinion = 0;
-
-	if (!debug_lockdep_rcu_enabled())
-		return 1;
-	if (!rcu_is_watching())
-		return 0;
-	if (!rcu_lockdep_current_cpu_online())
-		return 0;
-	if (debug_locks)
-		lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
-	return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
-}
+int rcu_read_lock_sched_held(void);
 #else /* #ifdef CONFIG_PREEMPT_COUNT */
 static inline int rcu_read_lock_sched_held(void)
 {
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index afaecb7a799a..fec5f48b8860 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -62,6 +62,55 @@ MODULE_ALIAS("rcupdate");
 
 module_param(rcu_expedited, int, 0);
 
+#if defined(CONFIG_DEBUG_LOCK_ALLOC) && defined(CONFIG_PREEMPT_COUNT)
+/**
+ * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
+ *
+ * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
+ * RCU-sched read-side critical section.  In absence of
+ * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
+ * critical section unless it can prove otherwise.  Note that disabling
+ * of preemption (including disabling irqs) counts as an RCU-sched
+ * read-side critical section.  This is useful for debug checks in functions
+ * that required that they be called within an RCU-sched read-side
+ * critical section.
+ *
+ * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
+ * and while lockdep is disabled.
+ *
+ * Note that if the CPU is in the idle loop from an RCU point of
+ * view (ie: that we are in the section between rcu_idle_enter() and
+ * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
+ * did an rcu_read_lock().  The reason for this is that RCU ignores CPUs
+ * that are in such a section, considering these as in extended quiescent
+ * state, so such a CPU is effectively never in an RCU read-side critical
+ * section regardless of what RCU primitives it invokes.  This state of
+ * affairs is required --- we need to keep an RCU-free window in idle
+ * where the CPU may possibly enter into low power mode. This way we can
+ * notice an extended quiescent state to other CPUs that started a grace
+ * period. Otherwise we would delay any grace period as long as we run in
+ * the idle task.
+ *
+ * Similarly, we avoid claiming an SRCU read lock held if the current
+ * CPU is offline.
+ */
+int rcu_read_lock_sched_held(void)
+{
+	int lockdep_opinion = 0;
+
+	if (!debug_lockdep_rcu_enabled())
+		return 1;
+	if (!rcu_is_watching())
+		return 0;
+	if (!rcu_lockdep_current_cpu_online())
+		return 0;
+	if (debug_locks)
+		lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
+	return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
+}
+EXPORT_SYMBOL(rcu_read_lock_sched_held);
+#endif
+
 #ifndef CONFIG_TINY_RCU
 
 static atomic_t rcu_expedited_nesting =
-- 
1.8.1.5

[PATCH tip/core/rcu 03/16] rcu: Change return type to bool

[Paul E. McKenney]

From: Nicholas Mc Guire <hofrat@osadl.org>

Type-checking coccinelle spatches are being used to locate type mismatches
between function signatures and return values in this case this produced:
./kernel/rcu/srcu.c:271 WARNING: return of wrong type
        int != unsigned long,

srcu_readers_active() returns an int that is the sum of per_cpu unsigned
long but the only user is cleanup_srcu_struct() which is using it as a
boolean (condition) to see if there is any readers rather than actually
using the approximate number of readers. The theoretically possible
unsigned long overflow case does not need to be handled explicitly - if
we had 4G++ readers then something else went wrong a long time ago.

proposal: change the return type to boolean. The function name is left
          unchanged as it fits the naming expectation for a boolean.

patch was compile tested for x86_64_defconfig (implies CONFIG_SRCU=y)

patch is against 4.1-rc5 (localversion-next is -next-20150525)

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/srcu.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index fb33d35ee0b7..de35087c92a5 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -252,14 +252,15 @@ static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx)
 }
 
 /**
- * srcu_readers_active - returns approximate number of readers.
+ * 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 int srcu_readers_active(struct srcu_struct *sp)
+static bool srcu_readers_active(struct srcu_struct *sp)
 {
 	int cpu;
 	unsigned long sum = 0;
-- 
1.8.1.5

[PATCH tip/core/rcu 04/16] rcu: Add RCU-sched flavors of get-state and cond-sync

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

The get_state_synchronize_rcu() and cond_synchronize_rcu() functions
allow polling for grace-period completion, with an actual wait for a
grace period occuring only when cond_synchronize_rcu() is called too
soon after the corresponding get_state_synchronize_rcu().  However,
these functions work only for vanilla RCU.  This commit adds the
get_state_synchronize_sched() and cond_synchronize_sched(), which provide
the same capability for RCU-sched.

Reported-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcutiny.h | 10 ++++++++++
 include/linux/rcutree.h |  2 ++
 kernel/rcu/rcutorture.c |  2 ++
 kernel/rcu/tree.c       | 52 +++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 66 insertions(+)

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 3df6c1ec4e25..ff968b7af3a4 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -37,6 +37,16 @@ static inline void cond_synchronize_rcu(unsigned long oldstate)
 	might_sleep();
 }
 
+static inline unsigned long get_state_synchronize_sched(void)
+{
+	return 0;
+}
+
+static inline void cond_synchronize_sched(unsigned long oldstate)
+{
+	might_sleep();
+}
+
 static inline void rcu_barrier_bh(void)
 {
 	wait_rcu_gp(call_rcu_bh);
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 456879143f89..5abec82f325e 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -76,6 +76,8 @@ void rcu_barrier_bh(void);
 void rcu_barrier_sched(void);
 unsigned long get_state_synchronize_rcu(void);
 void cond_synchronize_rcu(unsigned long oldstate);
+unsigned long get_state_synchronize_sched(void);
+void cond_synchronize_sched(unsigned long oldstate);
 
 extern unsigned long rcutorture_testseq;
 extern unsigned long rcutorture_vernum;
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 59e32684c23b..0f2cb55f0ab3 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -635,6 +635,8 @@ static struct rcu_torture_ops sched_ops = {
 	.deferred_free	= rcu_sched_torture_deferred_free,
 	.sync		= synchronize_sched,
 	.exp_sync	= synchronize_sched_expedited,
+	.get_state	= get_state_synchronize_sched,
+	.cond_sync	= cond_synchronize_sched,
 	.call		= call_rcu_sched,
 	.cb_barrier	= rcu_barrier_sched,
 	.fqs		= rcu_sched_force_quiescent_state,
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 8b5dd8ba9495..9629298eea24 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3253,6 +3253,58 @@ void cond_synchronize_rcu(unsigned long oldstate)
 }
 EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
 
+/**
+ * get_state_synchronize_sched - Snapshot current RCU-sched state
+ *
+ * Returns a cookie that is used by a later call to cond_synchronize_sched()
+ * to determine whether or not a full grace period has elapsed in the
+ * meantime.
+ */
+unsigned long get_state_synchronize_sched(void)
+{
+	/*
+	 * Any prior manipulation of RCU-protected data must happen
+	 * before the load from ->gpnum.
+	 */
+	smp_mb();  /* ^^^ */
+
+	/*
+	 * Make sure this load happens before the purportedly
+	 * time-consuming work between get_state_synchronize_sched()
+	 * and cond_synchronize_sched().
+	 */
+	return smp_load_acquire(&rcu_sched_state.gpnum);
+}
+EXPORT_SYMBOL_GPL(get_state_synchronize_sched);
+
+/**
+ * cond_synchronize_sched - Conditionally wait for an RCU-sched grace period
+ *
+ * @oldstate: return value from earlier call to get_state_synchronize_sched()
+ *
+ * If a full RCU-sched grace period has elapsed since the earlier call to
+ * get_state_synchronize_sched(), just return.  Otherwise, invoke
+ * synchronize_sched() to wait for a full grace period.
+ *
+ * Yes, this function does not take counter wrap into account.  But
+ * counter wrap is harmless.  If the counter wraps, we have waited for
+ * more than 2 billion grace periods (and way more on a 64-bit system!),
+ * so waiting for one additional grace period should be just fine.
+ */
+void cond_synchronize_sched(unsigned long oldstate)
+{
+	unsigned long newstate;
+
+	/*
+	 * Ensure that this load happens before any RCU-destructive
+	 * actions the caller might carry out after we return.
+	 */
+	newstate = smp_load_acquire(&rcu_sched_state.completed);
+	if (ULONG_CMP_GE(oldstate, newstate))
+		synchronize_sched();
+}
+EXPORT_SYMBOL_GPL(cond_synchronize_sched);
+
 static int synchronize_sched_expedited_cpu_stop(void *data)
 {
 	/*
-- 
1.8.1.5

[PATCH tip/core/rcu 05/16] rcu: Hide RCU_NOCB_CPU behind RCU_EXPERT

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

This commit prevents Kconfig from asking the user about RCU_NOCB_CPU
unless the user really wants to be asked.

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
 init/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/init/Kconfig b/init/Kconfig
index fdeff4ab5995..ba1e6eaf4c36 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -698,6 +698,7 @@ config RCU_BOOST_DELAY
 config RCU_NOCB_CPU
 	bool "Offload RCU callback processing from boot-selected CPUs"
 	depends on TREE_RCU || PREEMPT_RCU
+	depends on RCU_EXPERT || NO_HZ_FULL
 	default n
 	help
 	  Use this option to reduce OS jitter for aggressive HPC or
-- 
1.8.1.5

[PATCH tip/core/rcu 06/16] rcu: Use WRITE_ONCE in RCU_INIT_POINTER

[Paul E. McKenney]

From: Peter Zijlstra <peterz@infradead.org>

For the paranoid amongst us GCC would be in its right to use byte stores
to write our NULL value, tell it not to do that.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcupdate.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index def6d45ad61c..c63428c1ed8a 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -995,7 +995,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
 #define RCU_INIT_POINTER(p, v) \
 	do { \
 		rcu_dereference_sparse(p, __rcu); \
-		p = RCU_INITIALIZER(v); \
+		WRITE_ONCE(p, RCU_INITIALIZER(v)); \
 	} while (0)
 
 /**
-- 
1.8.1.5

[PATCH tip/core/rcu 07/16] rcu: Fix obsolete priority-boosting comment

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

Tasks are no longer migrated to the root rcu_node, so there is no
longer any need for a boost kthread for the root rcu_node, and there no
longer is such a kthread.  This commit therefore fixes the comment in
rcu_boost_kthread()'s header to reflect this new reality.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree_plugin.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 013485fb2b06..a983bc68a146 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1061,8 +1061,7 @@ static int rcu_boost(struct rcu_node *rnp)
 }
 
 /*
- * Priority-boosting kthread.  One per leaf rcu_node and one for the
- * root rcu_node.
+ * Priority-boosting kthread, one per leaf rcu_node.
  */
 static int rcu_boost_kthread(void *arg)
 {
-- 
1.8.1.5

[PATCH tip/core/rcu 08/16] rcu: Create a synchronize_rcu_mult()

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

There have been several requests for a primitive that waits for
grace periods for several RCU flavors concurrently, so this
commit creates it.  This is a variadic macro, and you pass in
the call_rcu() functions of the flavors of RCU that you wish to
wait for.

Note that you cannot pass in call_srcu() for two reasons: (1) This
would result in a type mismatch and (2) You need to specify which
srcu_struct you want to use.  Handle this by creating a wrapper
function for your SRCU domain, for example:

	void call_srcu_mine(struct rcu_head *head, rcu_callback_t func)
	{
		call_srcu(&ss_mine, head, func);
	}

You can then do something like this:

	synchronize_rcu_mult(call_srcu_mine, call_rcu, call_rcu_sched);

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcupdate.h | 35 +++++++++++++++++++++++++++++++----
 include/linux/types.h    |  3 +++
 kernel/rcu/update.c      | 37 +++++++++++++++++++++++++++----------
 3 files changed, 61 insertions(+), 14 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index c63428c1ed8a..33ec16b9c2ee 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -226,6 +226,37 @@ struct rcu_synchronize {
 };
 void wakeme_after_rcu(struct rcu_head *head);
 
+void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
+		   struct rcu_synchronize *rs_array);
+
+#define _wait_rcu_gp(checktiny, ...) \
+do { \
+	call_rcu_func_t __crcu_array[] = { __VA_ARGS__ }; \
+	const int __n = ARRAY_SIZE(__crcu_array); \
+	struct rcu_synchronize __rs_array[__n]; \
+	\
+	__wait_rcu_gp(checktiny, __n, __crcu_array, __rs_array); \
+} while (0)
+
+#define wait_rcu_gp(...) _wait_rcu_gp(false, __VA_ARGS__)
+
+/**
+ * synchronize_rcu_mult - Wait concurrently for multiple grace periods
+ * @...: List of call_rcu() functions for the flavors to wait on.
+ *
+ * This macro waits concurrently for multiple flavors of RCU grace periods.
+ * For example, synchronize_rcu_mult(call_rcu, call_rcu_bh) would wait
+ * on concurrent RCU and RCU-bh grace periods.  Waiting on a give SRCU
+ * domain requires you to write a wrapper function for that SRCU domain's
+ * call_srcu() function, supplying the corresponding srcu_struct.
+ *
+ * If Tiny RCU, tell _wait_rcu_gp() not to bother waiting for RCU
+ * or RCU-bh, given that anywhere synchronize_rcu_mult() can be called
+ * is automatically a grace period.
+ */
+#define synchronize_rcu_mult(...) \
+	_wait_rcu_gp(IS_ENABLED(CONFIG_TINY_RCU), __VA_ARGS__)
+
 /**
  * call_rcu_tasks() - Queue an RCU for invocation task-based grace period
  * @head: structure to be used for queueing the RCU updates.
@@ -392,10 +423,6 @@ bool __rcu_is_watching(void);
  * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
  */
 
-typedef void call_rcu_func_t(struct rcu_head *head,
-			     void (*func)(struct rcu_head *head));
-void wait_rcu_gp(call_rcu_func_t crf);
-
 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
 #include <linux/rcutree.h>
 #elif defined(CONFIG_TINY_RCU)
diff --git a/include/linux/types.h b/include/linux/types.h
index 8715287c3b1f..c314989d9158 100644
--- a/include/linux/types.h
+++ b/include/linux/types.h
@@ -212,6 +212,9 @@ struct callback_head {
 };
 #define rcu_head callback_head
 
+typedef void (*rcu_callback_t)(struct rcu_head *head);
+typedef void (*call_rcu_func_t)(struct rcu_head *head, rcu_callback_t func);
+
 /* clocksource cycle base type */
 typedef u64 cycle_t;
 
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index fec5f48b8860..a0a0dd03c73a 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -318,20 +318,37 @@ void wakeme_after_rcu(struct rcu_head *head)
 	rcu = container_of(head, struct rcu_synchronize, head);
 	complete(&rcu->completion);
 }
+EXPORT_SYMBOL_GPL(wakeme_after_rcu);
 
-void wait_rcu_gp(call_rcu_func_t crf)
+void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
+		   struct rcu_synchronize *rs_array)
 {
-	struct rcu_synchronize rcu;
+	int i;
 
-	init_rcu_head_on_stack(&rcu.head);
-	init_completion(&rcu.completion);
-	/* Will wake me after RCU finished. */
-	crf(&rcu.head, wakeme_after_rcu);
-	/* Wait for it. */
-	wait_for_completion(&rcu.completion);
-	destroy_rcu_head_on_stack(&rcu.head);
+	/* Initialize and register callbacks for each flavor specified. */
+	for (i = 0; i < n; i++) {
+		if (checktiny &&
+		    (crcu_array[i] == call_rcu ||
+		     crcu_array[i] == call_rcu_bh)) {
+			might_sleep();
+			continue;
+		}
+		init_rcu_head_on_stack(&rs_array[i].head);
+		init_completion(&rs_array[i].completion);
+		(crcu_array[i])(&rs_array[i].head, wakeme_after_rcu);
+	}
+
+	/* Wait for all callbacks to be invoked. */
+	for (i = 0; i < n; i++) {
+		if (checktiny &&
+		    (crcu_array[i] == call_rcu ||
+		     crcu_array[i] == call_rcu_bh))
+			continue;
+		wait_for_completion(&rs_array[i].completion);
+		destroy_rcu_head_on_stack(&rs_array[i].head);
+	}
 }
-EXPORT_SYMBOL_GPL(wait_rcu_gp);
+EXPORT_SYMBOL_GPL(__wait_rcu_gp);
 
 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
 void init_rcu_head(struct rcu_head *head)
-- 
1.8.1.5

[PATCH tip/core/rcu 09/16] cpu: Wait for RCU grace periods concurrently

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

In kernels built with CONFIG_PREEMPT, _cpu_down() waits for RCU and
RCU-sched grace periods back-to-back, incurring quite a bit more latency
than required.  This commit therefore uses the new synchronize_rcu_mult()
to allow waiting for both grace periods concurrently.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/cpu.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 9c9c9fab16cc..d63b062b6267 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -380,14 +380,14 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
 	 * will observe it.
 	 *
 	 * For CONFIG_PREEMPT we have preemptible RCU and its sync_rcu() might
-	 * not imply sync_sched(), so explicitly call both.
+	 * not imply sync_sched(), so wait for both.
 	 *
 	 * Do sync before park smpboot threads to take care the rcu boost case.
 	 */
-#ifdef CONFIG_PREEMPT
-	synchronize_sched();
-#endif
-	synchronize_rcu();
+	if (IS_ENABLED(CONFIG_PREEMPT))
+		synchronize_rcu_mult(call_rcu, call_rcu_sched);
+	else
+		synchronize_rcu();
 
 	smpboot_park_threads(cpu);
 
-- 
1.8.1.5

[PATCH tip/core/rcu 10/16] rcu: Make rcu_is_watching() really notrace

[Paul E. McKenney]

From: Alexei Starovoitov <ast@plumgrid.com>

Although rcu_is_watching() is marked notrace, it invokes preempt_disable()
and preempt_enable(), both of which can be traced.  This defeats the
purpose of the notrace on rcu_is_watching(), so this commit substitutes
preempt_disable_notrace() and preempt_enable_notrace().

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/rcu/tree.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 9629298eea24..cb64d7e13d24 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -978,9 +978,9 @@ bool notrace rcu_is_watching(void)
 {
 	bool ret;
 
-	preempt_disable();
+	preempt_disable_notrace();
 	ret = __rcu_is_watching();
-	preempt_enable();
+	preempt_enable_notrace();
 	return ret;
 }
 EXPORT_SYMBOL_GPL(rcu_is_watching);
-- 
1.8.1.5

[PATCH tip/core/rcu 11/16] rcu: Rename rcu_lockdep_assert() to RCU_LOCKDEP_WARN()

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

This commit renames rcu_lockdep_assert() to RCU_LOCKDEP_WARN() for
consistency with the WARN() series of macros.  This also requires
inverting the sense of the conditional, which this commit also does.

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
---
 Documentation/RCU/whatisRCU.txt  |  2 +-
 arch/x86/kernel/cpu/mcheck/mce.c |  6 ++--
 arch/x86/kernel/traps.c          |  2 +-
 drivers/base/power/opp.c         |  4 +--
 include/linux/fdtable.h          |  4 +--
 include/linux/rcupdate.h         | 63 ++++++++++++++++++++++++++--------------
 kernel/cgroup.c                  |  4 +--
 kernel/pid.c                     |  5 ++--
 kernel/rcu/srcu.c                | 10 +++----
 kernel/rcu/tiny.c                |  8 ++---
 kernel/rcu/tree.c                | 28 +++++++++---------
 kernel/rcu/tree_plugin.h         |  8 ++---
 kernel/rcu/update.c              |  4 +--
 kernel/sched/core.c              |  8 ++---
 kernel/workqueue.c               | 20 ++++++-------
 security/device_cgroup.c         |  6 ++--
 16 files changed, 101 insertions(+), 81 deletions(-)

diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index 5746b0c77f3e..adc2184009c5 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -883,7 +883,7 @@ All:  lockdep-checked RCU-protected pointer access
 
 	rcu_access_pointer
 	rcu_dereference_raw
-	rcu_lockdep_assert
+	RCU_LOCKDEP_WARN
 	rcu_sleep_check
 	RCU_NONIDLE
 
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index df919ff103c3..3d6b5269fb2e 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -54,9 +54,9 @@ static DEFINE_MUTEX(mce_chrdev_read_mutex);
 
 #define rcu_dereference_check_mce(p) \
 ({ \
-	rcu_lockdep_assert(rcu_read_lock_sched_held() || \
-			   lockdep_is_held(&mce_chrdev_read_mutex), \
-			   "suspicious rcu_dereference_check_mce() usage"); \
+	RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held() && \
+			 !lockdep_is_held(&mce_chrdev_read_mutex), \
+			 "suspicious rcu_dereference_check_mce() usage"); \
 	smp_load_acquire(&(p)); \
 })
 
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index f5791927aa64..c5a5231d1d11 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -136,7 +136,7 @@ enum ctx_state ist_enter(struct pt_regs *regs)
 	preempt_count_add(HARDIRQ_OFFSET);
 
 	/* This code is a bit fragile.  Test it. */
-	rcu_lockdep_assert(rcu_is_watching(), "ist_enter didn't work");
+	RCU_LOCKDEP_WARN(!rcu_is_watching(), "ist_enter didn't work");
 
 	return prev_state;
 }
diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c
index 677fb2843553..3b188f20b43f 100644
--- a/drivers/base/power/opp.c
+++ b/drivers/base/power/opp.c
@@ -110,8 +110,8 @@ static DEFINE_MUTEX(dev_opp_list_lock);
 
 #define opp_rcu_lockdep_assert()					\
 do {									\
-	rcu_lockdep_assert(rcu_read_lock_held() ||			\
-				lockdep_is_held(&dev_opp_list_lock),	\
+	RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&			\
+				!lockdep_is_held(&dev_opp_list_lock),	\
 			   "Missing rcu_read_lock() or "		\
 			   "dev_opp_list_lock protection");		\
 } while (0)
diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index fbb88740634a..674e3e226465 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -86,8 +86,8 @@ static inline struct file *__fcheck_files(struct files_struct *files, unsigned i
 
 static inline struct file *fcheck_files(struct files_struct *files, unsigned int fd)
 {
-	rcu_lockdep_assert(rcu_read_lock_held() ||
-			   lockdep_is_held(&files->file_lock),
+	RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
+			   !lockdep_is_held(&files->file_lock),
 			   "suspicious rcu_dereference_check() usage");
 	return __fcheck_files(files, fd);
 }
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 33ec16b9c2ee..ff476515f716 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -536,6 +536,11 @@ static inline int rcu_read_lock_sched_held(void)
 
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
+/* Deprecate rcu_lockdep_assert():  Use RCU_LOCKDEP_WARN() instead. */
+static inline void __attribute((deprecated)) deprecate_rcu_lockdep_assert(void)
+{
+}
+
 #ifdef CONFIG_PROVE_RCU
 
 /**
@@ -546,17 +551,32 @@ static inline int rcu_read_lock_sched_held(void)
 #define rcu_lockdep_assert(c, s)					\
 	do {								\
 		static bool __section(.data.unlikely) __warned;		\
+		deprecate_rcu_lockdep_assert();				\
 		if (debug_lockdep_rcu_enabled() && !__warned && !(c)) {	\
 			__warned = true;				\
 			lockdep_rcu_suspicious(__FILE__, __LINE__, s);	\
 		}							\
 	} while (0)
 
+/**
+ * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
+ * @c: condition to check
+ * @s: informative message
+ */
+#define RCU_LOCKDEP_WARN(c, s)						\
+	do {								\
+		static bool __section(.data.unlikely) __warned;		\
+		if (debug_lockdep_rcu_enabled() && !__warned && (c)) {	\
+			__warned = true;				\
+			lockdep_rcu_suspicious(__FILE__, __LINE__, s);	\
+		}							\
+	} while (0)
+
 #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
 static inline void rcu_preempt_sleep_check(void)
 {
-	rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
-			   "Illegal context switch in RCU read-side critical section");
+	RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
+			 "Illegal context switch in RCU read-side critical section");
 }
 #else /* #ifdef CONFIG_PROVE_RCU */
 static inline void rcu_preempt_sleep_check(void)
@@ -567,15 +587,16 @@ static inline void rcu_preempt_sleep_check(void)
 #define rcu_sleep_check()						\
 	do {								\
 		rcu_preempt_sleep_check();				\
-		rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),	\
-				   "Illegal context switch in RCU-bh read-side critical section"); \
-		rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),	\
-				   "Illegal context switch in RCU-sched read-side critical section"); \
+		RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map),	\
+				 "Illegal context switch in RCU-bh read-side critical section"); \
+		RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map),	\
+				 "Illegal context switch in RCU-sched read-side critical section"); \
 	} while (0)
 
 #else /* #ifdef CONFIG_PROVE_RCU */
 
-#define rcu_lockdep_assert(c, s) do { } while (0)
+#define rcu_lockdep_assert(c, s) deprecate_rcu_lockdep_assert()
+#define RCU_LOCKDEP_WARN(c, s) do { } while (0)
 #define rcu_sleep_check() do { } while (0)
 
 #endif /* #else #ifdef CONFIG_PROVE_RCU */
@@ -606,13 +627,13 @@ static inline void rcu_preempt_sleep_check(void)
 ({ \
 	/* Dependency order vs. p above. */ \
 	typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
-	rcu_lockdep_assert(c, "suspicious rcu_dereference_check() usage"); \
+	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
 	rcu_dereference_sparse(p, space); \
 	((typeof(*p) __force __kernel *)(________p1)); \
 })
 #define __rcu_dereference_protected(p, c, space) \
 ({ \
-	rcu_lockdep_assert(c, "suspicious rcu_dereference_protected() usage"); \
+	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
 	rcu_dereference_sparse(p, space); \
 	((typeof(*p) __force __kernel *)(p)); \
 })
@@ -836,8 +857,8 @@ static inline void rcu_read_lock(void)
 	__rcu_read_lock();
 	__acquire(RCU);
 	rcu_lock_acquire(&rcu_lock_map);
-	rcu_lockdep_assert(rcu_is_watching(),
-			   "rcu_read_lock() used illegally while idle");
+	RCU_LOCKDEP_WARN(!rcu_is_watching(),
+			 "rcu_read_lock() used illegally while idle");
 }
 
 /*
@@ -887,8 +908,8 @@ static inline void rcu_read_lock(void)
  */
 static inline void rcu_read_unlock(void)
 {
-	rcu_lockdep_assert(rcu_is_watching(),
-			   "rcu_read_unlock() used illegally while idle");
+	RCU_LOCKDEP_WARN(!rcu_is_watching(),
+			 "rcu_read_unlock() used illegally while idle");
 	__release(RCU);
 	__rcu_read_unlock();
 	rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
@@ -916,8 +937,8 @@ static inline void rcu_read_lock_bh(void)
 	local_bh_disable();
 	__acquire(RCU_BH);
 	rcu_lock_acquire(&rcu_bh_lock_map);
-	rcu_lockdep_assert(rcu_is_watching(),
-			   "rcu_read_lock_bh() used illegally while idle");
+	RCU_LOCKDEP_WARN(!rcu_is_watching(),
+			 "rcu_read_lock_bh() used illegally while idle");
 }
 
 /*
@@ -927,8 +948,8 @@ static inline void rcu_read_lock_bh(void)
  */
 static inline void rcu_read_unlock_bh(void)
 {
-	rcu_lockdep_assert(rcu_is_watching(),
-			   "rcu_read_unlock_bh() used illegally while idle");
+	RCU_LOCKDEP_WARN(!rcu_is_watching(),
+			 "rcu_read_unlock_bh() used illegally while idle");
 	rcu_lock_release(&rcu_bh_lock_map);
 	__release(RCU_BH);
 	local_bh_enable();
@@ -952,8 +973,8 @@ static inline void rcu_read_lock_sched(void)
 	preempt_disable();
 	__acquire(RCU_SCHED);
 	rcu_lock_acquire(&rcu_sched_lock_map);
-	rcu_lockdep_assert(rcu_is_watching(),
-			   "rcu_read_lock_sched() used illegally while idle");
+	RCU_LOCKDEP_WARN(!rcu_is_watching(),
+			 "rcu_read_lock_sched() used illegally while idle");
 }
 
 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
@@ -970,8 +991,8 @@ static inline notrace void rcu_read_lock_sched_notrace(void)
  */
 static inline void rcu_read_unlock_sched(void)
 {
-	rcu_lockdep_assert(rcu_is_watching(),
-			   "rcu_read_unlock_sched() used illegally while idle");
+	RCU_LOCKDEP_WARN(!rcu_is_watching(),
+			 "rcu_read_unlock_sched() used illegally while idle");
 	rcu_lock_release(&rcu_sched_lock_map);
 	__release(RCU_SCHED);
 	preempt_enable();
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f89d9292eee6..b89f3168411b 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -107,8 +107,8 @@ static DEFINE_SPINLOCK(release_agent_path_lock);
 struct percpu_rw_semaphore cgroup_threadgroup_rwsem;
 
 #define cgroup_assert_mutex_or_rcu_locked()				\
-	rcu_lockdep_assert(rcu_read_lock_held() ||			\
-			   lockdep_is_held(&cgroup_mutex),		\
+	RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&			\
+			   !lockdep_is_held(&cgroup_mutex),		\
 			   "cgroup_mutex or RCU read lock required");
 
 /*
diff --git a/kernel/pid.c b/kernel/pid.c
index 4fd07d5b7baf..ca368793808e 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -451,9 +451,8 @@ EXPORT_SYMBOL(pid_task);
  */
 struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
 {
-	rcu_lockdep_assert(rcu_read_lock_held(),
-			   "find_task_by_pid_ns() needs rcu_read_lock()"
-			   " protection");
+	RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
+			 "find_task_by_pid_ns() needs rcu_read_lock() protection");
 	return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
 }
 
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index de35087c92a5..d3fcb2ec8536 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -415,11 +415,11 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 	struct rcu_head *head = &rcu.head;
 	bool done = false;
 
-	rcu_lockdep_assert(!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 RCU) read-side critical section");
+	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");
 
 	might_sleep();
 	init_completion(&rcu.completion);
diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index c291bd65d2cb..d0471056d0af 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -191,10 +191,10 @@ static void rcu_process_callbacks(struct softirq_action *unused)
  */
 void synchronize_sched(void)
 {
-	rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
-			   !lock_is_held(&rcu_lock_map) &&
-			   !lock_is_held(&rcu_sched_lock_map),
-			   "Illegal synchronize_sched() in RCU read-side critical section");
+	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
+			 lock_is_held(&rcu_lock_map) ||
+			 lock_is_held(&rcu_sched_lock_map),
+			 "Illegal synchronize_sched() in RCU read-side critical section");
 	cond_resched();
 }
 EXPORT_SYMBOL_GPL(synchronize_sched);
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index cb64d7e13d24..0a73d26357a2 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -649,12 +649,12 @@ static void rcu_eqs_enter_common(long long oldval, bool user)
 	 * It is illegal to enter an extended quiescent state while
 	 * in an RCU read-side critical section.
 	 */
-	rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
-			   "Illegal idle entry in RCU read-side critical section.");
-	rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),
-			   "Illegal idle entry in RCU-bh read-side critical section.");
-	rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),
-			   "Illegal idle entry in RCU-sched read-side critical section.");
+	RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
+			 "Illegal idle entry in RCU read-side critical section.");
+	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map),
+			 "Illegal idle entry in RCU-bh read-side critical section.");
+	RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map),
+			 "Illegal idle entry in RCU-sched read-side critical section.");
 }
 
 /*
@@ -3161,10 +3161,10 @@ static inline int rcu_blocking_is_gp(void)
  */
 void synchronize_sched(void)
 {
-	rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
-			   !lock_is_held(&rcu_lock_map) &&
-			   !lock_is_held(&rcu_sched_lock_map),
-			   "Illegal synchronize_sched() in RCU-sched read-side critical section");
+	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
+			 lock_is_held(&rcu_lock_map) ||
+			 lock_is_held(&rcu_sched_lock_map),
+			 "Illegal synchronize_sched() in RCU-sched read-side critical section");
 	if (rcu_blocking_is_gp())
 		return;
 	if (rcu_gp_is_expedited())
@@ -3188,10 +3188,10 @@ EXPORT_SYMBOL_GPL(synchronize_sched);
  */
 void synchronize_rcu_bh(void)
 {
-	rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
-			   !lock_is_held(&rcu_lock_map) &&
-			   !lock_is_held(&rcu_sched_lock_map),
-			   "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
+	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
+			 lock_is_held(&rcu_lock_map) ||
+			 lock_is_held(&rcu_sched_lock_map),
+			 "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
 	if (rcu_blocking_is_gp())
 		return;
 	if (rcu_gp_is_expedited())
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index a983bc68a146..9e922f111d63 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -538,10 +538,10 @@ EXPORT_SYMBOL_GPL(call_rcu);
  */
 void synchronize_rcu(void)
 {
-	rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
-			   !lock_is_held(&rcu_lock_map) &&
-			   !lock_is_held(&rcu_sched_lock_map),
-			   "Illegal synchronize_rcu() in RCU read-side critical section");
+	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
+			 lock_is_held(&rcu_lock_map) ||
+			 lock_is_held(&rcu_sched_lock_map),
+			 "Illegal synchronize_rcu() in RCU read-side critical section");
 	if (!rcu_scheduler_active)
 		return;
 	if (rcu_gp_is_expedited())
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index a0a0dd03c73a..47268fb1d27b 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -589,8 +589,8 @@ EXPORT_SYMBOL_GPL(call_rcu_tasks);
 void synchronize_rcu_tasks(void)
 {
 	/* Complain if the scheduler has not started.  */
-	rcu_lockdep_assert(!rcu_scheduler_active,
-			   "synchronize_rcu_tasks called too soon");
+	RCU_LOCKDEP_WARN(rcu_scheduler_active,
+			 "synchronize_rcu_tasks called too soon");
 
 	/* Wait for the grace period. */
 	wait_rcu_gp(call_rcu_tasks);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 78b4bad10081..5e73c79fadd0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2200,8 +2200,8 @@ unsigned long to_ratio(u64 period, u64 runtime)
 #ifdef CONFIG_SMP
 inline struct dl_bw *dl_bw_of(int i)
 {
-	rcu_lockdep_assert(rcu_read_lock_sched_held(),
-			   "sched RCU must be held");
+	RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held(),
+			 "sched RCU must be held");
 	return &cpu_rq(i)->rd->dl_bw;
 }
 
@@ -2210,8 +2210,8 @@ static inline int dl_bw_cpus(int i)
 	struct root_domain *rd = cpu_rq(i)->rd;
 	int cpus = 0;
 
-	rcu_lockdep_assert(rcu_read_lock_sched_held(),
-			   "sched RCU must be held");
+	RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held(),
+			 "sched RCU must be held");
 	for_each_cpu_and(i, rd->span, cpu_active_mask)
 		cpus++;
 
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 4c4f06176f74..cb91c63b4f4a 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -338,20 +338,20 @@ static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
 #include <trace/events/workqueue.h>
 
 #define assert_rcu_or_pool_mutex()					\
-	rcu_lockdep_assert(rcu_read_lock_sched_held() ||		\
-			   lockdep_is_held(&wq_pool_mutex),		\
-			   "sched RCU or wq_pool_mutex should be held")
+	RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held() &&			\
+			 !lockdep_is_held(&wq_pool_mutex),		\
+			 "sched RCU or wq_pool_mutex should be held")
 
 #define assert_rcu_or_wq_mutex(wq)					\
-	rcu_lockdep_assert(rcu_read_lock_sched_held() ||		\
-			   lockdep_is_held(&wq->mutex),			\
-			   "sched RCU or wq->mutex should be held")
+	RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held() &&			\
+			 !lockdep_is_held(&wq->mutex),			\
+			 "sched RCU or wq->mutex should be held")
 
 #define assert_rcu_or_wq_mutex_or_pool_mutex(wq)			\
-	rcu_lockdep_assert(rcu_read_lock_sched_held() ||		\
-			   lockdep_is_held(&wq->mutex) ||		\
-			   lockdep_is_held(&wq_pool_mutex),		\
-			   "sched RCU, wq->mutex or wq_pool_mutex should be held")
+	RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held() &&			\
+			 !lockdep_is_held(&wq->mutex) &&		\
+			 !lockdep_is_held(&wq_pool_mutex),		\
+			 "sched RCU, wq->mutex or wq_pool_mutex should be held")
 
 #define for_each_cpu_worker_pool(pool, cpu)				\
 	for ((pool) = &per_cpu(cpu_worker_pools, cpu)[0];		\
diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 188c1d26393b..73455089feef 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -400,9 +400,9 @@ static bool verify_new_ex(struct dev_cgroup *dev_cgroup,
 {
 	bool match = false;
 
-	rcu_lockdep_assert(rcu_read_lock_held() ||
-			   lockdep_is_held(&devcgroup_mutex),
-			   "device_cgroup:verify_new_ex called without proper synchronization");
+	RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
+			 lockdep_is_held(&devcgroup_mutex),
+			 "device_cgroup:verify_new_ex called without proper synchronization");
 
 	if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 		if (behavior == DEVCG_DEFAULT_ALLOW) {
-- 
1.8.1.5

[PATCH tip/core/rcu 12/16] rcu: Fix backwards RCU_LOCKDEP_WARN() in synchronize_rcu_tasks()

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

The RCU_LOCKDEP_WARN() in synchronize_rcu_tasks() triggers if the
scheduler is active, which is backwards.  This commit therefore
negates the test.

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/update.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 47268fb1d27b..7a0b3bc7c5ed 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -589,7 +589,7 @@ EXPORT_SYMBOL_GPL(call_rcu_tasks);
 void synchronize_rcu_tasks(void)
 {
 	/* Complain if the scheduler has not started.  */
-	RCU_LOCKDEP_WARN(rcu_scheduler_active,
+	RCU_LOCKDEP_WARN(!rcu_scheduler_active,
 			 "synchronize_rcu_tasks called too soon");
 
 	/* Wait for the grace period. */
-- 
1.8.1.5

[PATCH tip/core/rcu 13/16] rcu: Clarify CONFIG_RCU_EQS_DEBUG help text

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 lib/Kconfig.debug | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index e2894b23efb6..26da2caa7d15 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1379,7 +1379,7 @@ config RCU_TRACE
 	  Say N if you are unsure.
 
 config RCU_EQS_DEBUG
-	bool "Use this when adding any sort of NO_HZ support to your arch"
+	bool "Provide debugging asserts for adding NO_HZ support to an arch"
 	depends on DEBUG_KERNEL
 	help
 	  This option provides consistency checks in RCU's handling of
-- 
1.8.1.5

[PATCH tip/core/rcu 14/16] rcu: update MAINTAINERS entry

[Paul E. McKenney]

From: Lai Jiangshan <laijs@cn.fujitsu.com>

This commit updates Lai Jiangshan's email address because the old
laijs@cn.fujitsu.com address will expire after July 10, 2015.

Signed-off-by: Lai Jiangshan <jiangshanlai@gmail.com>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 MAINTAINERS | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/MAINTAINERS b/MAINTAINERS
index 8133cefb6b6e..f92d8136a4a4 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8445,7 +8445,7 @@ M:	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
 M:	Josh Triplett <josh@joshtriplett.org>
 R:	Steven Rostedt <rostedt@goodmis.org>
 R:	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
-R:	Lai Jiangshan <laijs@cn.fujitsu.com>
+R:	Lai Jiangshan <jiangshanlai@gmail.com>
 L:	linux-kernel@vger.kernel.org
 S:	Supported
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
@@ -8472,7 +8472,7 @@ M:	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
 M:	Josh Triplett <josh@joshtriplett.org>
 R:	Steven Rostedt <rostedt@goodmis.org>
 R:	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
-R:	Lai Jiangshan <laijs@cn.fujitsu.com>
+R:	Lai Jiangshan <jiangshanlai@gmail.com>
 L:	linux-kernel@vger.kernel.org
 W:	http://www.rdrop.com/users/paulmck/RCU/
 S:	Supported
@@ -9340,7 +9340,7 @@ F:	include/linux/sl?b*.h
 F:	mm/sl?b*
 
 SLEEPABLE READ-COPY UPDATE (SRCU)
-M:	Lai Jiangshan <laijs@cn.fujitsu.com>
+M:	Lai Jiangshan <jiangshanlai@gmail.com>
 M:	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
 M:	Josh Triplett <josh@joshtriplett.org>
 R:	Steven Rostedt <rostedt@goodmis.org>
-- 
1.8.1.5

[PATCH tip/core/rcu 15/16] scripts: Make checkpatch.pl warn on expedited RCU grace periods

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

The synchronize_rcu_expedited() and synchronize_sched_expedited()
expedited-grace-period primitives induce OS jitter, which can degrade
real-time response.  This commit therefore adds a checkpatch.pl warning
on any patch adding them.

Note that this patch does not warn on synchronize_srcu_expedited()
because it does not induce OS jitter, courtesy of its otherwise
much-maligned read-side memory barriers.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Joe Perches <joe@perches.com>
---
 scripts/checkpatch.pl | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 90e1edc8dd42..0658a5f3029a 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -5011,6 +5011,7 @@ sub process {
 				     "memory barrier without comment\n" . $herecurr);
 			}
 		}
+
 # check for waitqueue_active without a comment.
 		if ($line =~ /\bwaitqueue_active\s*\(/) {
 			if (!ctx_has_comment($first_line, $linenr)) {
@@ -5018,6 +5019,24 @@ sub process {
 				     "waitqueue_active without comment\n" . $herecurr);
 			}
 		}
+
+# Check for expedited grace periods that interrupt non-idle non-nohz
+# online CPUs.  These expedited can therefore degrade real-time response
+# if used carelessly, and should be avoided where not absolutely
+# needed.  It is always OK to use synchronize_rcu_expedited() and
+# synchronize_sched_expedited() at boot time (before real-time applications
+# start) and in error situations where real-time response is compromised in
+# any case.  Note that synchronize_srcu_expedited() does -not- interrupt
+# other CPUs, so don't warn on uses of synchronize_srcu_expedited().
+# Of course, nothing comes for free, and srcu_read_lock() and
+# srcu_read_unlock() do contain full memory barriers in payment for
+# synchronize_srcu_expedited() non-interruption properties.
+		if ($line =~ /\b(synchronize_rcu_expedited|synchronize_sched_expedited)\(/) {
+			WARN("EXPEDITED_RCU_GRACE_PERIOD",
+			     "expedited RCU grace periods should be avoided in cases where they can degrade real-time response\n" . $herecurr);
+
+		}
+
 # check of hardware specific defines
 		if ($line =~ m@^.\s*\#\s*if.*\b(__i386__|__powerpc64__|__sun__|__s390x__)\b@ && $realfile !~ m@include/asm-@) {
 			CHK("ARCH_DEFINES",
-- 
1.8.1.5

[PATCH tip/core/rcu 16/16] rcu: Don't disable CPU hotplug during OOM notifiers

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

RCU's rcu_oom_notify() disables CPU hotplug in order to stabilize the
list of online CPUs, which it traverses.  However, this is completely
pointless because smp_call_function_single() will quietly fail if invoked
on an offline CPU.  Because the count of requests is incremented in the
rcu_oom_notify_cpu() function that is remotely invoked, everything works
nicely even in the face of concurrent CPU-hotplug operations.

Furthermore, in recent kernels, invoking get_online_cpus() from an OOM
notifier can result in deadlock.  This commit therefore removes the
call to get_online_cpus() and put_online_cpus() from rcu_oom_notify().

Reported-by: Marcin Ślusarz <marcin.slusarz@gmail.com>
Reported-by: David Rientjes <rientjes@google.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: David Rientjes <rientjes@google.com>
---
 kernel/rcu/tree_plugin.h | 2 --
 1 file changed, 2 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 9e922f111d63..80a7c17907fe 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1679,12 +1679,10 @@ static int rcu_oom_notify(struct notifier_block *self,
 	 */
 	atomic_set(&oom_callback_count, 1);
 
-	get_online_cpus();
 	for_each_online_cpu(cpu) {
 		smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
 		cond_resched_rcu_qs();
 	}
-	put_online_cpus();
 
 	/* Unconditionally decrement: no need to wake ourselves up. */
 	atomic_dec(&oom_callback_count);
-- 
1.8.1.5

Re: [PATCH tip/core/rcu 15/16] scripts: Make checkpatch.pl warn on expedited RCU grace periods

[Joe Perches]

On Fri, 2015-07-17 at 15:20 -0700, Paul E. McKenney wrote:
> The synchronize_rcu_expedited() and synchronize_sched_expedited()
> expedited-grace-period primitives induce OS jitter, which can degrade
> real-time response.  This commit therefore adds a checkpatch.pl warning
> on any patch adding them.
[]
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> +# Check for expedited grace periods that interrupt non-idle non-nohz
> +# online CPUs.  These expedited can therefore degrade real-time response
> +# if used carelessly, and should be avoided where not absolutely
> +# needed.  It is always OK to use synchronize_rcu_expedited() and
> +# synchronize_sched_expedited() at boot time (before real-time applications
> +# start) and in error situations where real-time response is compromised in
> +# any case.  Note that synchronize_srcu_expedited() does -not- interrupt
> +# other CPUs, so don't warn on uses of synchronize_srcu_expedited().
> +# Of course, nothing comes for free, and srcu_read_lock() and
> +# srcu_read_unlock() do contain full memory barriers in payment for
> +# synchronize_srcu_expedited() non-interruption properties.
> +		if ($line =~ /\b(synchronize_rcu_expedited|synchronize_sched_expedited)\(/) {

It'd be faster perl without capture groups:

		if ($line =~ /\b(?:synchronize_(?:rcu|sched)_expedited)\s*\(/) {

> +			WARN("EXPEDITED_RCU_GRACE_PERIOD",
> +			     "expedited RCU grace periods should be avoided in cases where they can degrade real-time response\n" . $herecurr);

"in cases" is rather redundant.

Re: [PATCH tip/core/rcu 15/16] scripts: Make checkpatch.pl warn on expedited RCU grace periods

[Paul E. McKenney]

On Fri, Jul 17, 2015 at 03:37:54PM -0700, Joe Perches wrote:
> On Fri, 2015-07-17 at 15:20 -0700, Paul E. McKenney wrote:
> > The synchronize_rcu_expedited() and synchronize_sched_expedited()
> > expedited-grace-period primitives induce OS jitter, which can degrade
> > real-time response.  This commit therefore adds a checkpatch.pl warning
> > on any patch adding them.
> []
> > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> []
> > +# Check for expedited grace periods that interrupt non-idle non-nohz
> > +# online CPUs.  These expedited can therefore degrade real-time response
> > +# if used carelessly, and should be avoided where not absolutely
> > +# needed.  It is always OK to use synchronize_rcu_expedited() and
> > +# synchronize_sched_expedited() at boot time (before real-time applications
> > +# start) and in error situations where real-time response is compromised in
> > +# any case.  Note that synchronize_srcu_expedited() does -not- interrupt
> > +# other CPUs, so don't warn on uses of synchronize_srcu_expedited().
> > +# Of course, nothing comes for free, and srcu_read_lock() and
> > +# srcu_read_unlock() do contain full memory barriers in payment for
> > +# synchronize_srcu_expedited() non-interruption properties.
> > +		if ($line =~ /\b(synchronize_rcu_expedited|synchronize_sched_expedited)\(/) {
> 
> It'd be faster perl without capture groups:
> 
> 		if ($line =~ /\b(?:synchronize_(?:rcu|sched)_expedited)\s*\(/) {

Fair enough, but this pattern is used rather heavily in this script,
and I don't trust my perl enough to want to create a new pattern.

I see a couple of possible ways forward:

1.	I hand this patch off to you, and you update it as you deem fit.

2.	I push the patch as is (after the fix below) and you update
	checkpatch as a whole to use the more efficient code.

How would you like to proceed?

> > +			WARN("EXPEDITED_RCU_GRACE_PERIOD",
> > +			     "expedited RCU grace periods should be avoided in cases where they can degrade real-time response\n" . $herecurr);
> 
> "in cases" is rather redundant.

I did make this change.

								Thanx, Paul

Re: [PATCH tip/core/rcu 15/16] scripts: Make checkpatch.pl warn on expedited RCU grace periods

[Joe Perches]

On Mon, 2015-07-20 at 17:41 -0700, Paul E. McKenney wrote:
> On Fri, Jul 17, 2015 at 03:37:54PM -0700, Joe Perches wrote:
> > It'd be faster perl without capture groups:
> > 
> > 		if ($line =~ /\b(?:synchronize_(?:rcu|sched)_expedited)\s*\(/) {
> 
> Fair enough, but this pattern is used rather heavily in this script,
> and I don't trust my perl enough to want to create a new pattern.
> 
> I see a couple of possible ways forward:
> 
> 1.	I hand this patch off to you, and you update it as you deem fit.
> 
> 2.	I push the patch as is (after the fix below) and you update
> 	checkpatch as a whole to use the more efficient code.
> 
> How would you like to proceed?

Push and fix would work fine.

Re: [PATCH tip/core/rcu 15/16] scripts: Make checkpatch.pl warn on expedited RCU grace periods

[Steven Rostedt]

On Fri, 17 Jul 2015 15:37:54 -0700
Joe Perches <joe@perches.com> wrote:

> > +		if ($line =~ /\b(synchronize_rcu_expedited|synchronize_sched_expedited)\(/) {
> 
> It'd be faster perl without capture groups:

Is checkpatch such a critical code path that we could possibly notice
the difference in speed? Although the above may be few microseconds
slower, to me, the above looks a hell of a lot more readable.

-- Steve

Re: [PATCH tip/core/rcu 15/16] scripts: Make checkpatch.pl warn on expedited RCU grace periods

[Paul E. McKenney]

On Mon, Jul 20, 2015 at 05:48:40PM -0700, Joe Perches wrote:
> On Mon, 2015-07-20 at 17:41 -0700, Paul E. McKenney wrote:
> > On Fri, Jul 17, 2015 at 03:37:54PM -0700, Joe Perches wrote:
> > > It'd be faster perl without capture groups:
> > > 
> > > 		if ($line =~ /\b(?:synchronize_(?:rcu|sched)_expedited)\s*\(/) {
> > 
> > Fair enough, but this pattern is used rather heavily in this script,
> > and I don't trust my perl enough to want to create a new pattern.
> > 
> > I see a couple of possible ways forward:
> > 
> > 1.	I hand this patch off to you, and you update it as you deem fit.
> > 
> > 2.	I push the patch as is (after the fix below) and you update
> > 	checkpatch as a whole to use the more efficient code.
> > 
> > How would you like to proceed?
> 
> Push and fix would work fine.

Very good, will do!

							Thanx, Paul

Re: [PATCH tip/core/rcu 15/16] scripts: Make checkpatch.pl warn on expedited RCU grace periods

[Joe Perches]

On Mon, 2015-07-20 at 20:55 -0400, Steven Rostedt wrote:
> On Fri, 17 Jul 2015 15:37:54 -0700
> Joe Perches <joe@perches.com> wrote:
> 
> > > +		if ($line =~ /\b(synchronize_rcu_expedited|synchronize_sched_expedited)\(/) {
> > 
> > It'd be faster perl without capture groups:
> 
> Is checkpatch such a critical code path that we could possibly notice
> the difference in speed? Although the above may be few microseconds
> slower, to me, the above looks a hell of a lot more readable.

Regardless, it's not as capable as it wouldn't find
any miswritten form like

	synchronize_<foo>_expedited ( args... )

Re: [PATCH tip/core/rcu 15/16] scripts: Make checkpatch.pl warn on expedited RCU grace periods

[Steven Rostedt]

On Mon, 20 Jul 2015 18:06:19 -0700
Joe Perches <joe@perches.com> wrote:

> On Mon, 2015-07-20 at 20:55 -0400, Steven Rostedt wrote:
> > On Fri, 17 Jul 2015 15:37:54 -0700
> > Joe Perches <joe@perches.com> wrote:
> > 
> > > > +		if ($line =~ /\b(synchronize_rcu_expedited|synchronize_sched_expedited)\(/) {
> > > 
> > > It'd be faster perl without capture groups:
> > 
> > Is checkpatch such a critical code path that we could possibly notice
> > the difference in speed? Although the above may be few microseconds
> > slower, to me, the above looks a hell of a lot more readable.
> 
> Regardless, it's not as capable as it wouldn't find
> any miswritten form like
> 
> 	synchronize_<foo>_expedited ( args... )

Then that's a better rational than performance.

-- Steve

Re: [PATCH tip/core/rcu 15/16] scripts: Make checkpatch.pl warn on expedited RCU grace periods

[Paul E. McKenney]

On Mon, Jul 20, 2015 at 06:06:19PM -0700, Joe Perches wrote:
> On Mon, 2015-07-20 at 20:55 -0400, Steven Rostedt wrote:
> > On Fri, 17 Jul 2015 15:37:54 -0700
> > Joe Perches <joe@perches.com> wrote:
> > 
> > > > +		if ($line =~ /\b(synchronize_rcu_expedited|synchronize_sched_expedited)\(/) {
> > > 
> > > It'd be faster perl without capture groups:
> > 
> > Is checkpatch such a critical code path that we could possibly notice
> > the difference in speed? Although the above may be few microseconds
> > slower, to me, the above looks a hell of a lot more readable.
> 
> Regardless, it's not as capable as it wouldn't find
> any miswritten form like
> 
> 	synchronize_<foo>_expedited ( args... )

Hmmm...  My current patch doesn't complain about this:

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

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 77192953dee5..89577b8d3ba6 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -492,6 +492,8 @@ static void srcu_read_delay(struct torture_random_state *rrsp)
 	const long uspertick = 1000000 / HZ;
 	const long longdelay = 10;
 
+	synchronize_srcu_expedited(srcu_ctlp);
+
 	/* We want there to be long-running readers, but not all the time. */
 
 	delay = torture_random(rrsp) %

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

But it does correctly complain when I add synchronize_rcu_expedited()
or synchronize_sched_expedited().

So what am I missing here?

							Thanx, Paul

Re: [PATCH tip/core/rcu 15/16] scripts: Make checkpatch.pl warn on expedited RCU grace periods

[Joe Perches]

On Mon, 2015-07-20 at 18:29 -0700, Paul E. McKenney wrote:
> On Mon, Jul 20, 2015 at 06:06:19PM -0700, Joe Perches wrote:
> > On Mon, 2015-07-20 at 20:55 -0400, Steven Rostedt wrote:
> > > On Fri, 17 Jul 2015 15:37:54 -0700
> > > Joe Perches <joe@perches.com> wrote:
> > > 
> > > > > +		if ($line =~ /\b(synchronize_rcu_expedited|synchronize_sched_expedited)\(/) {
> > > > 
> > > > It'd be faster perl without capture groups:
> > > 
> > > Is checkpatch such a critical code path that we could possibly notice
> > > the difference in speed? Although the above may be few microseconds
> > > slower, to me, the above looks a hell of a lot more readable.
> > 
> > Regardless, it's not as capable as it wouldn't find
> > any miswritten form like
> > 
> > 	synchronize_<foo>_expedited ( args... )
> 
> Hmmm...  My current patch doesn't complain about this:
> 
> ------------------------------------------------------------------------
> 
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index 77192953dee5..89577b8d3ba6 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -492,6 +492,8 @@ static void srcu_read_delay(struct torture_random_state *rrsp)
>  	const long uspertick = 1000000 / HZ;
>  	const long longdelay = 10;
>  
> +	synchronize_srcu_expedited(srcu_ctlp);
> +
>  	/* We want there to be long-running readers, but not all the time. */
>  
>  	delay = torture_random(rrsp) %
> 
> ------------------------------------------------------------------------
> 
> But it does correctly complain when I add synchronize_rcu_expedited()
> or synchronize_sched_expedited().
> 
> So what am I missing here?

A space between the function name and the open parenthesis

Re: [PATCH tip/core/rcu 15/16] scripts: Make checkpatch.pl warn on expedited RCU grace periods

[Paul E. McKenney]

On Mon, Jul 20, 2015 at 06:58:03PM -0700, Joe Perches wrote:
> On Mon, 2015-07-20 at 18:29 -0700, Paul E. McKenney wrote:
> > On Mon, Jul 20, 2015 at 06:06:19PM -0700, Joe Perches wrote:
> > > On Mon, 2015-07-20 at 20:55 -0400, Steven Rostedt wrote:
> > > > On Fri, 17 Jul 2015 15:37:54 -0700
> > > > Joe Perches <joe@perches.com> wrote:
> > > > 
> > > > > > +		if ($line =~ /\b(synchronize_rcu_expedited|synchronize_sched_expedited)\(/) {
> > > > > 
> > > > > It'd be faster perl without capture groups:
> > > > 
> > > > Is checkpatch such a critical code path that we could possibly notice
> > > > the difference in speed? Although the above may be few microseconds
> > > > slower, to me, the above looks a hell of a lot more readable.
> > > 
> > > Regardless, it's not as capable as it wouldn't find
> > > any miswritten form like
> > > 
> > > 	synchronize_<foo>_expedited ( args... )
> > 
> > Hmmm...  My current patch doesn't complain about this:
> > 
> > ------------------------------------------------------------------------
> > 
> > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> > index 77192953dee5..89577b8d3ba6 100644
> > --- a/kernel/rcu/rcutorture.c
> > +++ b/kernel/rcu/rcutorture.c
> > @@ -492,6 +492,8 @@ static void srcu_read_delay(struct torture_random_state *rrsp)
> >  	const long uspertick = 1000000 / HZ;
> >  	const long longdelay = 10;
> >  
> > +	synchronize_srcu_expedited(srcu_ctlp);
> > +
> >  	/* We want there to be long-running readers, but not all the time. */
> >  
> >  	delay = torture_random(rrsp) %
> > 
> > ------------------------------------------------------------------------
> > 
> > But it does correctly complain when I add synchronize_rcu_expedited()
> > or synchronize_sched_expedited().
> > 
> > So what am I missing here?
> 
> A space between the function name and the open parenthesis

Got it, thank you!

							Thanx, Paul

Re: [PATCH tip/core/rcu 15/16] scripts: Make checkpatch.pl warn on expedited RCU grace periods

[Joe Perches]

On Mon, 2015-07-20 at 21:15 -0400, Steven Rostedt wrote:
> On Mon, 20 Jul 2015 18:06:19 -0700 Joe Perches <joe@perches.com> wrote:
> > On Mon, 2015-07-20 at 20:55 -0400, Steven Rostedt wrote:
> > > On Fri, 17 Jul 2015 15:37:54 -0700
> > > Joe Perches <joe@perches.com> wrote:
> > > > > +		if ($line =~ /\b(synchronize_rcu_expedited|synchronize_sched_expedited)\(/) {
> > > > It'd be faster perl without capture groups:
> > > Is checkpatch such a critical code path that we could possibly notice
> > > the difference in speed? Although the above may be few microseconds
> > > slower, to me, the above looks a hell of a lot more readable.

Not to me. Compact is generally more readable.

> > Regardless, it's not as capable as it wouldn't find
> > any miswritten form like
> > 
> > 	synchronize_<foo>_expedited ( args... )
> 
> Then that's a better rational than performance.

Part and parcel.

Regardless, I'll send a patch once it's actually pushed.

Re: [PATCH tip/core/rcu 15/16] scripts: Make checkpatch.pl warn on expedited RCU grace periods

[Paul E. McKenney]

On Tue, Jul 21, 2015 at 10:18:06AM -0700, Joe Perches wrote:
> On Mon, 2015-07-20 at 21:15 -0400, Steven Rostedt wrote:
> > On Mon, 20 Jul 2015 18:06:19 -0700 Joe Perches <joe@perches.com> wrote:
> > > On Mon, 2015-07-20 at 20:55 -0400, Steven Rostedt wrote:
> > > > On Fri, 17 Jul 2015 15:37:54 -0700
> > > > Joe Perches <joe@perches.com> wrote:
> > > > > > +		if ($line =~ /\b(synchronize_rcu_expedited|synchronize_sched_expedited)\(/) {
> > > > > It'd be faster perl without capture groups:
> > > > Is checkpatch such a critical code path that we could possibly notice
> > > > the difference in speed? Although the above may be few microseconds
> > > > slower, to me, the above looks a hell of a lot more readable.
> 
> Not to me. Compact is generally more readable.
> 
> > > Regardless, it's not as capable as it wouldn't find
> > > any miswritten form like
> > > 
> > > 	synchronize_<foo>_expedited ( args... )
> > 
> > Then that's a better rational than performance.
> 
> Part and parcel.
> 
> Regardless, I'll send a patch once it's actually pushed.

Current plan is to push it into the upcoming merge window.

							Thanx, Paul