linux-kernel - [tip: sched/urgent] sched: Avoid double preemption in __cond_resched

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Message-ID: <164250468946.16921.3796443718413078010.tip-bot2@tip-bot2>
Date:   Tue, 18 Jan 2022 11:18:09 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     xuhaifeng <xuhaifeng@...o.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/urgent] sched: Avoid double preemption in __cond_resched_*lock*()

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     7e406d1ff39b8ee574036418a5043c86723170cf
Gitweb:        https://git.kernel.org/tip/7e406d1ff39b8ee574036418a5043c86723170cf
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Sat, 25 Dec 2021 01:04:57 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 18 Jan 2022 12:09:59 +01:00

sched: Avoid double preemption in __cond_resched_*lock*()

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
---
 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 0d2ab2a..56b428c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8218,9 +8218,7 @@ 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);
@@ -8238,9 +8236,7 @@ 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);
@@ -8258,9 +8254,7 @@ 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);