Messages in this thread | | | Date | Tue, 22 Nov 2011 15:28:02 +0100 | Subject | Re: [PATCH] perf_event: fix loss of notification with multi-event sampling | From | Stephane Eranian <> |
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On Tue, Nov 22, 2011 at 3:13 PM, Stephane Eranian <eranian@google.com> wrote: > On Tue, Nov 22, 2011 at 2:29 PM, Peter Zijlstra <peterz@infradead.org> wrote: >> On Tue, 2011-11-22 at 14:15 +0100, Stephane Eranian wrote: >> >>> > Ah, could it be a race of poll()/wakeup() vs perf_event_set_output() ? >>> > >>> Are you saying that by dropping event->waitq in favor of event->rb->waitq >>> we make this problem disappear due to rcu protections? >> >> Well, except.. >> >>> Poll_wait() is a blocking call. It may wait on a stale waitq. But that problem >>> was probably already there. I am not clear as to what to do about that. >>> in perf_set_output() you would need to wakeup from poll_wait() and then >>> go back in with the new waitq. >> >> Right, the whole blocking thing is a problem, and the whole poll() >> interface always makes my head hurt. >> >> If there was a go-sleep and wake-up side to poll we could do >> ring_buffer_get()/put() and fix this problem, but I'm not finding a way >> to make that happen quite yet. >> >>> Similarly, I am not clear as to what happens when you close an event for >>> which you have a waiter in poll_wait(). I assume you wakeup from it. >>> But I don't see where that's implemented. >> >> Good point, yes we should do that. >> > I looked at how this is done for regular files: eventpoll_release(file);
Well, but's that called as part of __fput(), which is called before fops->release(). So it should do it, unless you have to set some more flags in poll(), i.e., more than POLLIN. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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