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    SubjectRe: [PATCH,RFC] perf: panic due to inclied cpu context task_ctx value
    On Mon, 2011-03-28 at 16:57 +0200, Peter Zijlstra wrote:
    > >
    > > Wait... Yes, we have to clear ctx->is_active, otherwise we break, say,
    > > perf_install_in_context().
    > >
    > > But if we clear ->is_active we break perf_event_enable(). Suppose we
    > > are doing ioctl(PERF_EVENT_IOC_DISABLE) + ioctl(PERF_EVENT_IOC_ENABLE).
    > > PERF_EVENT_IOC_DISABLE can sched_out the last event, but _IOC_ENABLE
    > > treats ctx->is_active == F as "it is not running".
    > Right, same for the tick, if say we can only schedule 1 event at a time
    > and we close the 1 event that is active, the tick will not rotate a new
    > event in.

    Another fun race, suppose we do properly remove task_ctx and is_active,
    but then the task gets scheduled back in before free_event() gets around
    to disabling the jump_label..

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