From: Peter Zijlstra <peterz@infradead.org>
Date: Sat, 25 Dec 2021 00:04:57 +0000 (+0100)
Subject: sched: Avoid double preemption in __cond_resched_*lock*()
X-Git-Tag: Ubuntu-5.15.0-23.23~802
X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=c57d75a0fa16586ba84ad37fd15cdaa986d402bf;p=mirror_ubuntu-jammy-kernel.git

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

BugLink: https://bugs.launchpad.net/bugs/1963889

[ 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@oppo.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/YcGnvDEYBwOiV0cR@hirez.programming.kicks-ass.net
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>
---

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index df505a153198..4230fc1d40b0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8200,9 +8200,7 @@ 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);
@@ -8220,9 +8218,7 @@ 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);
@@ -8240,9 +8236,7 @@ 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);