linux-kernel - Re: [sched/pelt] e906550aca: WARNING:at_kernel/sched/fair.c:#update_blocked

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Date:   Thu, 3 Jun 2021 12:59:33 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     kernel test robot <oliver.sang@...el.com>,
        0day robot <lkp@...el.com>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
        ltp@...ts.linux.it, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Odin Ugedal <odin@...d.al>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Chen Yu <yu.c.chen@...el.com>
Subject: Re: [sched/pelt] e906550aca: WARNING:at_kernel/sched/fair.c:#update_blocked_averages

Hi Dietmar,

On Thu, 3 Jun 2021 at 12:50, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>
> On 02/06/2021 08:45, kernel test robot wrote:
>
> [...]
>
> > kern :warn : [   40.989618] WARNING: CPU: 2 PID: 253 at kernel/sched/fair.c:8029 update_blocked_averages (kbuild/src/consumer/kernel/sched/fair.c:8029 kbuild/src/consumer/kernel/sched/fair.c:8065 kbuild/src/consumer/kernel/sched/fair.c:8152)
>
> Hit something like this on my Ubuntu i7-7567U as well.

Thanks for having a look at this.

>
> With more debugging:
>
> [    7.388006] WARNING: CPU: 1 PID: 926 at kernel/sched/fair.c:8029 update_blocked_averages+0x30d/0x7e0
> ...
> [    7.388167] path=/autogroup-2 load_avg=1 util_avg=0 runnable_avg=1
>
> IMHO, this is because this patch needs:
>
> (1) sched/pelt: ensure that *_sum is always synced with *_avg (2021-06-03 Vincent Guittot)
>
> https://lkml.kernel.org/r/20210601085832.12626-1-vincent.guittot@linaro.org
>
> (2) sched/fair: Keep load_avg and load_sum synced (2021-06-03 Vincent Guittot)
>
> tip/sched/urgent 7c7ad626d9a0
>
> Using both patches underneath makes this warning go away.

I haven't spent time on this but that's also my 1st guess for the root cause

Regards,
Vincent

>