linux-kernel - [PATCH AUTOSEL 5.16 18/52] sched: Avoid double preemption in __cond_resched

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Date:   Thu,  3 Feb 2022 15:29:12 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        xuhaifeng <xuhaifeng@...o.com>, Sasha Levin <sashal@...nel.org>,
        mingo@...hat.com, juri.lelli@...hat.com, vincent.guittot@...aro.org
Subject: [PATCH AUTOSEL 5.16 18/52] sched: Avoid double preemption in __cond_resched_*lock*()

From: Peter Zijlstra <peterz@...radead.org>

[ Upstream commit 7e406d1ff39b8ee574036418a5043c86723170cf ]

For PREEMPT/DYNAMIC_PREEMPT the *_unlock() will already trigger a
preemption, no point in then calling preempt_schedule_common()
*again*.

Use _cond_resched() instead, since this is a NOP for the preemptible
configs while it provide a preemption point for the others.

Reported-by: xuhaifeng <xuhaifeng@...o.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/YcGnvDEYBwOiV0cR@hirez.programming.kicks-ass.net
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/sched/core.c | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 77563109c0ea0..d24823b3c3f9f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8176,9 +8176,7 @@ int __cond_resched_lock(spinlock_t *lock)
 
 	if (spin_needbreak(lock) || resched) {
 		spin_unlock(lock);
-		if (resched)
-			preempt_schedule_common();
-		else
+		if (!_cond_resched())
 			cpu_relax();
 		ret = 1;
 		spin_lock(lock);
@@ -8196,9 +8194,7 @@ int __cond_resched_rwlock_read(rwlock_t *lock)
 
 	if (rwlock_needbreak(lock) || resched) {
 		read_unlock(lock);
-		if (resched)
-			preempt_schedule_common();
-		else
+		if (!_cond_resched())
 			cpu_relax();
 		ret = 1;
 		read_lock(lock);
@@ -8216,9 +8212,7 @@ int __cond_resched_rwlock_write(rwlock_t *lock)
 
 	if (rwlock_needbreak(lock) || resched) {
 		write_unlock(lock);
-		if (resched)
-			preempt_schedule_common();
-		else
+		if (!_cond_resched())
 			cpu_relax();
 		ret = 1;
 		write_lock(lock);
-- 
2.34.1