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

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Message-ID: <CABk29Nv=Gj9H0dfvdV0E9us+jBnysoPXYoO-Rkn46rwGtg7=hA@mail.gmail.com>
Date: Mon, 30 Sep 2024 13:26:08 -0700
From: Josh Don <joshdon@...gle.com>
To: Waiman Long <longman@...hat.com>, Ingo Molnar <mingo@...hat.com>, 
	Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>, 
	Vincent Guittot <vincent.guittot@...aro.org>
Cc: 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 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've also collected the following:

Acked-by: Waiman Long <longman@...hat.com>
Tested-by: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>

Best,
Josh