[PATCH tip/core/rcu 0/3] SRCU updates for v5.9

[PATCH tip/core/rcu 0/3] SRCU updates for v5.9

[Paul E. McKenney]

Hello!

This series provides SRCU updates.

1.	Fix a typo in comment "amoritized"->"amortized", courtesy of
	Ethon Paul.

2.	Avoid local_irq_save() before acquiring spinlock_t, courtesy
	of Sebastian Andrzej Siewior.

3.	Remove KCSAN stubs.

							Thanx, Paul

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

 srcutree.c |   29 ++++++++---------------------
 1 file changed, 8 insertions(+), 21 deletions(-)

[PATCH tip/core/rcu 1/3] srcu: Fix a typo in comment "amoritized"->"amortized"

[paulmck]

From: Ethon Paul <ethp@qq.com>

This commit fixes a typo in a comment.

Signed-off-by: Ethon Paul <ethp@qq.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/srcutree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 6d3ef70..8ff71e5 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -766,7 +766,7 @@ static void srcu_flip(struct srcu_struct *ssp)
  * it, if this function was preempted for enough time for the counters
  * to wrap, it really doesn't matter whether or not we expedite the grace
  * period.  The extra overhead of a needlessly expedited grace period is
- * negligible when amoritized over that time period, and the extra latency
+ * negligible when amortized over that time period, and the extra latency
  * of a needlessly non-expedited grace period is similarly negligible.
  */
 static bool srcu_might_be_idle(struct srcu_struct *ssp)
-- 
2.9.5

[PATCH tip/core/rcu 2/3] srcu: Avoid local_irq_save() before acquiring spinlock_t

[paulmck]

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

SRCU disables interrupts to get a stable per-CPU pointer and then
acquires the spinlock which is in the per-CPU data structure. The
release uses spin_unlock_irqrestore(). While this is correct on a non-RT
kernel, this conflicts with the RT semantics because the spinlock is
converted to a 'sleeping' spinlock. Sleeping locks can obviously not be
acquired with interrupts disabled.

Acquire the per-CPU pointer `ssp->sda' without disabling preemption and
then acquire the spinlock_t of the per-CPU data structure. The lock will
ensure that the data is consistent.

The added call to check_init_srcu_struct() is now needed because a
statically defined srcu_struct may remain uninitialized until this
point and the newly introduced locking operation requires an initialized
spinlock_t.

This change was tested for four hours with 8*SRCU-N and 8*SRCU-P without
causing any warnings.

Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: rcu@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/srcutree.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 8ff71e5..c100acf 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -777,14 +777,15 @@ static bool srcu_might_be_idle(struct srcu_struct *ssp)
 	unsigned long t;
 	unsigned long tlast;
 
+	check_init_srcu_struct(ssp);
 	/* If the local srcu_data structure has callbacks, not idle.  */
-	local_irq_save(flags);
-	sdp = this_cpu_ptr(ssp->sda);
+	sdp = raw_cpu_ptr(ssp->sda);
+	spin_lock_irqsave_rcu_node(sdp, flags);
 	if (rcu_segcblist_pend_cbs(&sdp->srcu_cblist)) {
-		local_irq_restore(flags);
+		spin_unlock_irqrestore_rcu_node(sdp, flags);
 		return false; /* Callbacks already present, so not idle. */
 	}
-	local_irq_restore(flags);
+	spin_unlock_irqrestore_rcu_node(sdp, flags);
 
 	/*
 	 * No local callbacks, so probabalistically probe global state.
@@ -864,9 +865,8 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 	}
 	rhp->func = func;
 	idx = srcu_read_lock(ssp);
-	local_irq_save(flags);
-	sdp = this_cpu_ptr(ssp->sda);
-	spin_lock_rcu_node(sdp);
+	sdp = raw_cpu_ptr(ssp->sda);
+	spin_lock_irqsave_rcu_node(sdp, flags);
 	rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
 	rcu_segcblist_advance(&sdp->srcu_cblist,
 			      rcu_seq_current(&ssp->srcu_gp_seq));
-- 
2.9.5

[PATCH tip/core/rcu 3/3] srcu: Remove KCSAN stubs

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

KCSAN is now in mainline, so this commit removes the stubs for the
data_race(), ASSERT_EXCLUSIVE_WRITER(), and ASSERT_EXCLUSIVE_ACCESS()
macros.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/srcutree.c | 13 -------------
 1 file changed, 13 deletions(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index c100acf..c13348e 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -29,19 +29,6 @@
 #include "rcu.h"
 #include "rcu_segcblist.h"
 
-#ifndef data_race
-#define data_race(expr)							\
-	({								\
-		expr;							\
-	})
-#endif
-#ifndef ASSERT_EXCLUSIVE_WRITER
-#define ASSERT_EXCLUSIVE_WRITER(var) do { } while (0)
-#endif
-#ifndef ASSERT_EXCLUSIVE_ACCESS
-#define ASSERT_EXCLUSIVE_ACCESS(var) do { } while (0)
-#endif
-
 /* Holdoff in nanoseconds for auto-expediting. */
 #define DEFAULT_SRCU_EXP_HOLDOFF (25 * 1000)
 static ulong exp_holdoff = DEFAULT_SRCU_EXP_HOLDOFF;
-- 
2.9.5