linux-kernel - Re: [PATCH] sched/core: Print out straggler tasks in sched_cpu

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Message-ID: <20210114152207.GI2743@paulmck-ThinkPad-P72>
Date:   Thu, 14 Jan 2021 07:22:07 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...nel.org, tglx@...utronix.de, jiangshanlai@...il.com,
        cai@...hat.com, vincent.donnefort@....com, decui@...rosoft.com,
        vincent.guittot@...aro.org, rostedt@...dmis.org, tj@...nel.org
Subject: Re: [PATCH] sched/core: Print out straggler tasks in
 sched_cpu_dying()

On Thu, Jan 14, 2021 at 10:37:35AM +0000, Valentin Schneider wrote:
> On 13/01/21 16:36, Paul E. McKenney wrote:
> > On Thu, Jan 14, 2021 at 12:15:24AM +0000, Valentin Schneider wrote:
> >> On 13/01/21 14:02, Paul E. McKenney wrote:
> >> Thanks for giving it a spin! I think with the current series (either
> >> Lai's or Peter's) sched_cpu_dying() should go smoothly, but you never
> >> know.
> >
> > I was running the patch set having one of Lai's and three of Peter's,
> > which sounds like Peter's.
> 
> That's how I was seeing it :)

If someone can identify Lai's series to me, I would be happy to give it
a try as well.  All I see are workqueue-specific patches and patches
contributing to the discussion of possible fixes to the splats from
Peter's series.  (I figured that I would wait for the discussion to
converge a bit.)

> > If I understand which series is which,
> > Peter's has the advantage of not requiring rcutorture changes.  ;-)
> >
> >> > However, it did produce the following new-to-me splat, which will
> >> > hopefully be of some help.
> >> >
> >> >                                                       Thanx, Paul
> >> >
> >> > ------------------------------------------------------------------------
> >> >
> >> > WARNING: CPU: 2 PID: 23 at kernel/kthread.c:508 kthread_set_per_cpu+0x3b/0x50
> >>
> >> Aha, so that's that warning I was expecting to see [1].
> >> Did you also get the process_one_work() one?
> >
> > Yes.  Of 112 one-hour runs, there were five process_one_work() splats
> > and two kthread_set_per_cpu() splats.  Each splat-ridden run had exactly
> > one splat.
> 
> I was expecting to see both in one run, so am still somewhat confused.

Well, if we weren't confused in some way or another, the bug would not
exist, so I will count becoming aware of confusion as a step forward.  ;-)

							Thanx, Paul