linux-kernel - Re: WARNING: at arch/x86/kernel/cpu/perf

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Date:	Mon, 6 Feb 2012 15:41:40 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: WARNING: at arch/x86/kernel/cpu/perf_event.c:989

On Mon, Feb 6, 2012 at 3:38 PM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Stephane Eranian <eranian@...gle.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

> Thanks,
>
>        Ingo
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