Messages in this thread | | | Subject | Re: [PATCH] perf_event: fix loss of notification with multi-event sampling | From | Peter Zijlstra <> | Date | Tue, 22 Nov 2011 14:29:19 +0100 |
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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.
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