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From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Fri, 12 Nov 2021 08:50:46 +0100
Message-ID: <CAKfTPtDaO9KGhWGYnr6CNRy=h1UuVXTJEqcVFz3dzvi=xqMv4A@mail.gmail.com>
Subject: Re: printk deadlock due to double lock attempt on current CPU's runqueue
To:     Sultan Alsawaf <sultan@kerneltoast.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Anton Vorontsov <anton@enomsg.org>,
        Ben Segall <bsegall@google.com>,
        Colin Cross <ccross@android.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        David Airlie <airlied@linux.ie>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        dri-devel@lists.freedesktop.org, Ingo Molnar <mingo@redhat.com>,
        John Ogness <john.ogness@linutronix.de>,
        Juri Lelli <juri.lelli@redhat.com>,
        Kees Cook <keescook@chromium.org>,
        linux-kernel@vger.kernel.org,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Mel Gorman <mgorman@suse.de>, Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Tony Luck <tony.luck@intel.com>, mkoutny@suse.com
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On Wed, 10 Nov 2021 at 20:50, Sultan Alsawaf <sultan@kerneltoast.com> wrote:
>
> On Wed, Nov 10, 2021 at 10:00:35AM +0100, Vincent Guittot wrote:
> > Is it the same SCHED_WARN_ON(rq->tmp_alone_branch !=
> > &rq->leaf_cfs_rq_list); that generates the deadlock on v5.15 too ?
> >
> > one remaining tmp_alone_branch warning has been fixed in v5.15 with
> > 2630cde26711 ("sched/fair: Add ancestors of unthrottled undecayed cfs_rq")
>
> I should clarify that I didn't actually reproduce the issue on v5.15; I just saw
> that the call chain leading to the deadlock still existed in v5.15 after looking
> through the code.

Thanks for the clarification

>
> Failing the SCHED_WARN_ON(rq->tmp_alone_branch != &rq->leaf_cfs_rq_list); assert
> is extremely rare in my experience, and I don't have a reproducer. It has only
> happened once after months of heavy usage (with lots of reboots too, so not with
> crazy high uptime).
>
> Sultan