Re: [PATCH] sched: fix warning in sched_setaffinity

[Vincent Guittot]

On Mon, 30 Sept 2024 at 22:26, Josh Don <joshdon@xxxxxxxxxx> wrote:
>
> On Thu, Aug 29, 2024 at 3:04 PM Josh Don <joshdon@xxxxxxxxxx> 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@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>

>
> I've also collected the following:
>
> Acked-by: Waiman Long <longman@xxxxxxxxxx>
> Tested-by: Madadi Vineeth Reddy <vineethr@xxxxxxxxxxxxx>
>
> Best,
> Josh