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From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Wed, 4 Mar 2020 16:26:15 +0100
Message-ID: <CAKfTPtD9b6o=B6jkbWNjfAw9e1UjT9Z07vxdsVfikEQdeCtfPw@mail.gmail.com>
Subject: Re: 5.6-rc3: WARNING: CPU: 48 PID: 17435 at kernel/sched/fair.c:380 enqueue_task_fair+0x328/0x440
To:     Christian Borntraeger <borntraeger@de.ibm.com>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On Tue, 3 Mar 2020 at 08:55, Vincent Guittot <vincent.guittot@linaro.org> wrote:
>
> On Tue, 3 Mar 2020 at 08:37, Christian Borntraeger
> <borntraeger@de.ibm.com> wrote:
> >
> >
> >
[...]
> > >>> ---
> > >>>  kernel/sched/fair.c | 2 +-
> > >>>  1 file changed, 1 insertion(+), 1 deletion(-)
> > >>>
> > >>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > >>> index 3c8a379c357e..beb773c23e7d 100644
> > >>> --- a/kernel/sched/fair.c
> > >>> +++ b/kernel/sched/fair.c
> > >>> @@ -4035,8 +4035,8 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
> > >>>             __enqueue_entity(cfs_rq, se);
> > >>>     se->on_rq = 1;
> > >>>
> > >>> +   list_add_leaf_cfs_rq(cfs_rq);
> > >>>     if (cfs_rq->nr_running == 1) {
> > >>> -           list_add_leaf_cfs_rq(cfs_rq);
> > >>>             check_enqueue_throttle(cfs_rq);
> > >>>     }
> > >>>  }
> > >>
> > >> Now running for 3 hours. I have not seen the issue yet. I can tell tomorrow if this fixes
> > >> the issue.
> > >
> > >
> > > Still running fine. I can tell for sure tomorrow, but I have the impression that this makes the
> > > WARN_ON go away.
> >
> > So I guess this change "fixed" the issue. If you want me to test additional patches, let me know.
>
> Thanks for the test. For now, I don't have any other patch to test. I
> have to look more deeply how the situation happens.
> I will let you know if I have other patch to test

So I haven't been able to figure out how we reach this situation yet.
In the meantime I'm going to make a clean patch with the fix above.

Is it ok if I add a reported -by and a tested-by you ?

>
> >