From: Tejun Heo <tj@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Yu Peng <pengyu@kylinos.cn>,
mingo@redhat.com, juri.lelli@redhat.com,
vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
vschneid@redhat.com, jiangshanlai@gmail.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] sched,workqueue: Use READ_ONCE()/WRITE_ONCE() for wake_cpu accesses
Date: Fri, 27 Mar 2026 07:04:20 -1000 [thread overview]
Message-ID: <aca4lM-AsEdstYCf@slm.duckdns.org> (raw)
In-Reply-To: <20260327092739.GB3739027@noisy.programming.kicks-ass.net>
Hello,
On Fri, Mar 27, 2026 at 10:27:39AM +0100, Peter Zijlstra wrote:
> On Fri, Mar 27, 2026 at 03:30:07PM +0800, Yu Peng wrote:
> > task_struct->wake_cpu is used as a wake placement hint by scheduler code
> > and workqueue's non-strict affinity repatriation path.
> >
> > These accesses are intentionally lockless and stale values are tolerated,
> > affecting only wakeup placement.
>
> The scheduler usage isn't lockless. And I'm not at all sure why and how
> workqueue is poking at this stuff :/ It has no business poking at it.
Oh, you were involved in the discussion. It's workqueue using ->wake_cpu as
a way to implement opportunistic affinity at work boundaries as past history
doesn't mean anything at these boundaries.
https://lore.kernel.org/all/20230519001709.2563-1-tj@kernel.org/
Hmmm... it would trigger KCSAN. Maybe a better way to do it is exposing
sched interface that does WRITE_ONCE wrapping? How do you want it resolved?
Thanks.
--
tejun
next prev parent reply other threads:[~2026-03-27 17:04 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-27 7:30 [PATCH] sched,workqueue: Use READ_ONCE()/WRITE_ONCE() for wake_cpu accesses Yu Peng
2026-03-27 9:27 ` Peter Zijlstra
2026-03-27 17:04 ` Tejun Heo [this message]
2026-03-30 14:36 ` Peter Zijlstra
2026-03-30 20:09 ` Tejun Heo
2026-03-30 20:26 ` Tejun Heo
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