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

    * 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
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