linux-kernel - Re: [PATCH] sched: fix warning in sched

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Message-ID: <CAKfTPtALrwODTP8ZunfKgun75mr5OVsXB_KMmLxeFxjyKkrCyg@mail.gmail.com>
Date: Tue, 1 Oct 2024 11:50:02 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Josh Don <joshdon@...gle.com>
Cc: Waiman Long <longman@...hat.com>, Ingo Molnar <mingo@...hat.com>, 
	Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>, 
	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>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: fix warning in sched_setaffinity

On Mon, 30 Sept 2024 at 22:26, Josh Don <joshdon@...gle.com> wrote:
>
> On Thu, Aug 29, 2024 at 3:04 PM Josh Don <joshdon@...gle.com> wrote:
> >
> > Commit 8f9ea86fdf99b added some logic to sched_setaffinity that included
> > a WARN when a per-task affinity assignment races with a cpuset update.
> >
> > Specifically, we can have a race where a cpuset update results in the
> > task affinity no longer being a subset of the cpuset. That's fine; we
> > have a fallback to instead use the cpuset mask. However, we have a WARN
> > set up that will trigger if the cpuset mask has no overlap at all with
> > the requested task affinity. This shouldn't be a warning condition; its
> > trivial to create this condition.
> >
> > Reproduced the warning by the following setup:
> >
> > - $PID inside a cpuset cgroup
> > - another thread repeatedly switching the cpuset cpus from 1-2 to just 1
> > - another thread repeatedly setting the $PID affinity (via taskset) to 2
> >
> > Fixes: 8f9ea86fdf99b ("sched: Always preserve the user requested cpumask")
> > Signed-off-by: Josh Don <joshdon@...gle.com>
>
> Gentle ping to bump this in case it got lost.

I have also been able to reproduce the race and the WARN with the
steps described in the commit description

Acked-and-tested-by: Vincent Guittot <vincent.guittot@...aro.org>

>
> I've also collected the following:
>
> Acked-by: Waiman Long <longman@...hat.com>
> Tested-by: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
>
> Best,
> Josh