linux-kernel - [tip: perf/urgent] perf/core: Fix the WARN_ON

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Message-ID: <175137502738.406.18395407234477293993.tip-bot2@tip-bot2>
Date: Tue, 01 Jul 2025 13:03:47 -0000
From: "tip-bot2 for Luo Gengkun" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Luo Gengkun <luogengkun@...weicloud.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: perf/urgent] perf/core: Fix the WARN_ON_ONCE is out of lock
 protected region

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

Commit-ID:     7b4c5a37544ba22c6ebe72c0d4ea56c953459fa5
Gitweb:        https://git.kernel.org/tip/7b4c5a37544ba22c6ebe72c0d4ea56c953459fa5
Author:        Luo Gengkun <luogengkun@...weicloud.com>
AuthorDate:    Thu, 26 Jun 2025 13:54:03 
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Mon, 30 Jun 2025 09:32:49 +02:00

perf/core: Fix the WARN_ON_ONCE is out of lock protected region

commit 3172fb986666 ("perf/core: Fix WARN in perf_cgroup_switch()") try to
fix a concurrency problem between perf_cgroup_switch and
perf_cgroup_event_disable. But it does not to move the WARN_ON_ONCE into
lock-protected region, so the warning is still be triggered.

Fixes: 3172fb986666 ("perf/core: Fix WARN in perf_cgroup_switch()")
Signed-off-by: Luo Gengkun <luogengkun@...weicloud.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20250626135403.2454105-1-luogengkun@huaweicloud.com
---
 kernel/events/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7281230..bf2118c 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -951,8 +951,6 @@ static void perf_cgroup_switch(struct task_struct *task)
 	if (READ_ONCE(cpuctx->cgrp) == NULL)
 		return;
 
-	WARN_ON_ONCE(cpuctx->ctx.nr_cgroups == 0);
-
 	cgrp = perf_cgroup_from_task(task, NULL);
 	if (READ_ONCE(cpuctx->cgrp) == cgrp)
 		return;
@@ -964,6 +962,8 @@ static void perf_cgroup_switch(struct task_struct *task)
 	if (READ_ONCE(cpuctx->cgrp) == NULL)
 		return;
 
+	WARN_ON_ONCE(cpuctx->ctx.nr_cgroups == 0);
+
 	perf_ctx_disable(&cpuctx->ctx, true);
 
 	ctx_sched_out(&cpuctx->ctx, NULL, EVENT_ALL|EVENT_CGROUP);