Re: WARNING: at arch/x86/kernel/cpu/perf_event.c:989

From: Stephane Eranian
Date: Mon Feb 06 2012 - 09:41:40 EST

On Mon, Feb 6, 2012 at 3:38 PM, Ingo Molnar <mingo@xxxxxxx> wrote:
> * Stephane Eranian <eranian@xxxxxxxxxx> 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:
>> Â Â Â stop()
>> Â Â Â if (delta > 0) {
>> Â Â Â Â Â Âperf_adjust_period() {
>> Â Â Â Â Â Â Â Âif (period > 8*...) {
>> Â Â Â Â Â Â Â Â Â Âstop()
>> Â Â Â Â Â Â Â Â Â Â...
>> Â Â Â Â Â Â Â Â Â Âstart()
>> Â Â Â Â Â Â Â Â}
>> Â Â Â Â Â Â}
>> Â Â Â Â}
>> Â Â Â Âstart()
>> 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:
> Â84f2b9b2edc0: 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,
> Â Â Â ÂIngo
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