On Fri, Dec 11, 2015 at 03:36:36PM +0200, Alexander Shishkin wrote:
> +static int __perf_event_itrace_filters_setup(void *info)
> +{
> + struct perf_event *event = info;
> + int ret;
> +
> + if (READ_ONCE(event->state) != PERF_EVENT_STATE_ACTIVE)
> + return -EAGAIN;
> +
> + /* matches smp_wmb() in event_sched_in() */
> + smp_rmb();
> +
> + /*
> + * There is a window with interrupts enabled before we get here,
> + * so we need to check again lest we try to stop another cpu's event.
> + */
> + if (READ_ONCE(event->oncpu) != smp_processor_id())
> + return -EAGAIN;
> +
> + event->pmu->stop(event, PERF_EF_UPDATE);
> + rcu_read_lock();
> + ret = event->pmu->itrace_filter_setup(event);
> + rcu_read_unlock();
> + event->pmu->start(event, PERF_EF_RELOAD);
Would it not be more sensible to let the ::itrace_filter_setup() method
do the stop/start-ing if and when needed?
> +
> + return ret;
> +}
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