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Date: Mon, 6 Feb 2012 16:47:01 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Stephane Eranian <eranian@google.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
        Markus Trippelsdorf <markus@trippelsdorf.de>,
        linux-kernel@vger.kernel.org, Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Paul Mackerras <paulus@samba.org>
Subject: Re: WARNING: at arch/x86/kernel/cpu/perf_event.c:989
Message-ID: <20120206154700.GA13478@elte.hu>
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* Stephane Eranian <eranian@google.com> wrote:

> On Mon, Feb 6, 2012 at 3:38 PM, Ingo Molnar <mingo@elte.hu> wrote:
> >
> > * Stephane Eranian <eranian@google.com> wrote:
> >
> >> Ok, I found the problem!
> >>
> >> it comes from perf_adjust_freq_unthr_context() vs perf_adjust_period().
> >> The latter can under certain condition stop and restart the event. So we
> >> had:
> >>
> >>       stop()
> >>       if (delta > 0) {
> >>            perf_adjust_period() {
> >>                if (period > 8*...) {
> >>                    stop()
> >>                    ...
> >>                    start()
> >>                }
> >>            }
> >>        }
> >>        start()
> >>
> >> Could have a double stop() and double start(), thus triggering the warning in
> >> x86_pmu_start().
> >>
> >> Will post a patch shortly to fix this.
> >
> > Please send a patch against tip:master (or perf/urgent), on top
> > of:
> >
> >  84f2b9b2edc0: perf: Remove deprecated WARN_ON_ONCE()
> >
> > Note that I updated that patch to removed one more WARN_ON()
> > than you originally sent - please add it back as appropriate, in
> > the delta fix patch.
> >
> I have already added the warning back. Will send against tip:master

Great - thanks!

	Ingo