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From:   Josh Don <joshdon@google.com>
Date:   Thu, 29 Apr 2021 16:22:04 -0700
Message-ID: <CABk29NuM98UEmbxD9OY8TLab0yNbrT5ASJ8ELyUw6ZOZq1j7Zg@mail.gmail.com>
Subject: Re: [PATCH 04/19] sched: Prepare for Core-wide rq->lock
To:     Don Hiatt <dhiatt@digitalocean.com>
Cc:     Aubrey Li <aubrey.intel@gmail.com>,
        Aubrey Li <aubrey.li@linux.intel.com>,
        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 Thu, Apr 29, 2021 at 2:09 PM Don Hiatt <dhiatt@digitalocean.com> wrote:
>
> On Thu, Apr 29, 2021 at 1:48 PM Josh Don <joshdon@google.com> wrote:
> >
> > On Wed, Apr 28, 2021 at 9:41 AM Don Hiatt <dhiatt@digitalocean.com> wrote:
> > >
> > > I'm still seeing hard lockups while repeatedly setting cookies on qemu
> > > processes even with
> > > the updated patch. If there is any debug you'd like me to turn on,
> > > just let me know.
> > >
> > > Thanks!
> > >
> > > don
> >
> > Thanks for the added context on your repro configuration. In addition
> > to the updated patch from earlier, could you try the modification to
> > double_rq_lock() from
> > https://lkml.kernel.org/r/CABk29NuS-B3n4sbmavo0NDA1OCCsz6Zf2VDjjFQvAxBMQoJ_Lg@mail.gmail.com
> > ? I have a feeling this is what's causing your lockup.
> >
> > Best,
> > Josh
>
> Hi Josh,
>
> I've been running Aubrey+Peter's patch (attached) for almost 5 hours
> and haven't had a single issue. :)
>
> I'm running a set-cookie script every 5 seconds on the two VMs (each
> vm is running
> 'sysbench --threads=1 --time=0 cpu run' to generate some load in the vm) and
> I'm running two of the same sysbench runs on the HV while setting cookies
> every 5 seconds.
>
> Unless I jinxed us it looks like a great fix. :)
>
> Let me know if there is anything else you'd like me to try. I'm going
> to leave the tests running
> and see what happens. I update with what I find.
>
> Thanks!
>
> don

That's awesome news, thanks for validating. Note that with Aubrey's
patch there is still a race window if sched core is being
enabled/disabled (ie. if you alternate between there being some
cookies in the system, and no cookies). In my reply I posted an
alternative version to avoid that. If your script were to do the
on-off flipping with the old patch, you'd might eventually see another
lockup.