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From:   Josh Don <joshdon@google.com>
Date:   Tue, 27 Apr 2021 16:35:07 -0700
Message-ID: <CABk29Nuz-FDCk23ajcr9gS4KD-wMpwyn=ASu+yuTTT445rwTvw@mail.gmail.com>
Subject: Re: [PATCH 04/19] sched: Prepare for Core-wide rq->lock
To:     Don Hiatt <dhiatt@digitalocean.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        "Hyser,Chris" <chris.hyser@oracle.com>,
        Ingo Molnar <mingo@kernel.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Mel Gorman <mgorman@suse.de>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>
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On Tue, Apr 27, 2021 at 10:10 AM Don Hiatt <dhiatt@digitalocean.com> wrote:
> Hi Josh and Peter,
>
> I've been running into soft lookups and hard lockups when running a script
> that just cycles setting the cookie of a group of processes over and over again.
>
> Unfortunately the only way I can reproduce this is by setting the cookies
> on qemu. I've tried sysbench, stress-ng but those seem to work just fine.
>
> I'm running Peter's branch and even tried the suggested changes here but
> still see the same behavior. I enabled panic on hard lockup and here below
> is a snippet of the log.
>
> Is there anything you'd like me to try or have any debugging you'd like me to
> do? I'd certainly like to get to the bottom of this.

Hi Don,

I tried to repro using qemu, but did not generate a lockup. Could you
provide more details on what your script is doing (or better yet,
share the script directly)? I would have expected you to potentially
hit a lockup if you were cycling sched_core being enabled and
disabled, but it sounds like you are just recreating the cookie for a
process group over and over?

Best,
Josh