linux-kernel - [PATCH] sched/ext: Suppress warning in __this_cpu

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20250716-scx_warning-v1-1-0e814f78eb8c@debian.org>
Date: Wed, 16 Jul 2025 05:46:15 -0700
From: Breno Leitao <leitao@...ian.org>
To: Tejun Heo <tj@...nel.org>, David Vernet <void@...ifault.com>, 
 Andrea Righi <arighi@...dia.com>, Changwoo Min <changwoo@...lia.com>, 
 Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
 Juri Lelli <juri.lelli@...hat.com>, 
 Vincent Guittot <vincent.guittot@...aro.org>, 
 Dietmar Eggemann <dietmar.eggemann@....com>, 
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, 
 Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>
Cc: sched-ext@...ts.linux.dev, linux-kernel@...r.kernel.org, 
 kernel-team@...a.com, jake@...lion.co.uk, Breno Leitao <leitao@...ian.org>
Subject: [PATCH] sched/ext: Suppress warning in __this_cpu_write() by
 disabling preemption

__this_cpu_write() emits a warning if used with preemption enabled.

Function update_locked_rq() might be called with preemption enabled,
which causes the following warning:

	BUG: using __this_cpu_write() in preemptible [00000000] code: scx_layered_6-9/68770

Disable preemption around the __this_cpu_write() call in
update_locked_rq() to suppress the warning, without affecting behavior.

If preemption triggers a  jump to another CPU during the callback it's
fine, since we would track the rq state on the other CPU with its own
local variable.

Suggested-by: Andrea Righi <arighi@...dia.com>
Signed-off-by: Breno Leitao <leitao@...ian.org>
Fixes: 18853ba782bef ("sched_ext: Track currently locked rq")
Acked-by: Andrea Righi <arighi@...dia.com>
---
 kernel/sched/ext.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index b498d867ba210..24fcbd7331f73 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -1258,7 +1258,14 @@ static inline void update_locked_rq(struct rq *rq)
 	 */
 	if (rq)
 		lockdep_assert_rq_held(rq);
+	/*
+	 * __this_cpu_write() emits a warning when used with preemption enabled.
+	 * While there's no functional issue if the callback runs on another
+	 * CPU, we disable preemption here solely to suppress that warning.
+	 */
+	preempt_disable();
 	__this_cpu_write(locked_rq, rq);
+	preempt_enable();
 }
 
 /*

---
base-commit: 155a3c003e555a7300d156a5252c004c392ec6b0
change-id: 20250716-scx_warning-5143cf17f806

Best regards,
--  
Breno Leitao <leitao@...ian.org>