linux-kernel - Re: Perf hotplug lockup in v4.9-rc8

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Date:   Wed, 7 Dec 2016 16:39:25 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        jeremy.linton@....com
Subject: Re: Perf hotplug lockup in v4.9-rc8

On Wed, Dec 07, 2016 at 02:30:58PM +0000, Mark Rutland wrote:
> On Wed, Dec 07, 2016 at 01:52:17PM +0000, Mark Rutland wrote:
> > Hi all
> > 
> > Jeremy noticed a kernel lockup on arm64 when the perf tool was used in
> > parallel with hotplug, which I've reproduced on arm64 and x86(-64) with
> > v4.9-rc8. In both cases I'm using defconfig; I've tried enabling lockdep
> > but it was silent for arm64 and x86.
> > 
> > I haven't yet tested earlier kernels and I'm not sure how long this has
> > been around for; I'm currently building a v4.8 defconfig to compare
> > with. In the meantime, info dump below.
> 
> On v4.8 it hangs on x86, but my SSH session survived. Log below; I'll
> give v4.7 a go...

It seems the lockup has been around at least since v4.6, so I'll give up
trying to find a point when it didn't exist.

Peter had some ideas over IRC, so I'll give those a go atop of v4.9-rc8.

Thanks,
Mark.