On Tue, Jun 22, 2021 at 07:24:56PM +0200, Oleksandr Natalenko wrote:
> Hello.
>
> On úterý 22. června 2021 18:47:59 CEST Greg KH wrote:
> > On Tue, Jun 22, 2021 at 06:30:46PM +0200, Oleksandr Natalenko wrote:
> > > I'd like to nominate d583d360a6 ("psi: Fix psi state corruption when
> > > schedule() races with cgroup move") for 5.12 stable tree.
> > >
> > > Recently, I've hit this:
> > >
> > > ```
> > > kernel: psi: inconsistent task state! task=2667:clementine cpu=21
> > > psi_flags=0 clear=1 set=0
> > > ```
> > >
> > > and after that PSI IO went crazy high. That seems to match the symptoms
> > > described in the commit message.
> >
> > But this says it fixes 4117cebf1a9f ("psi: Optimize task switch inside
> > shared cgroups") which did not show up until 5.13-rc1, so how are you
> > hitting this issue?
>
> I'm not positive 4117cebf1a9f was a root cause of the race. To me it looks
> like 4117cebf1a9f just made an older issue more likely to be hit.
>
> Peter, Johannes, am I correct saying that it is still possible to hit a
> corruption described in d583d360a6 on 5.12?
I'm not aware of a previous issue, but it's possible you discovered
one that was incidentally fixed by this change.
That said, there haven't been many changes in this area prior to 5.12,
and I stared at the old code quite a bit to see if there are other
possible scenarios, so this gives me pause.
> > Did you try this patch on 5.12.y and see that it solved your problem?
>
> Yes, I've built the kernel with this patch, and so far it runs fine. It can
> take a while until the condition is hit though since it seems to be very
> unlikely on 5.12.
Is your task moving / being moved between cgroups while it's doing
work?
How long does it usually take to trigger it?
Would it be possible to share a simpler reproducer, or is this part of
a more complex application?
