Messages in this thread | ![/](/images/icornerl.gif) | | Date | Tue, 9 Nov 2010 18:42:20 +0100 | From | Oleg Nesterov <> | Subject | Re: Q: perf_event && event->owner |
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On 11/09, Peter Zijlstra wrote: > > Ah,.. quite so. So how about we explicitly destroy the list when the > task dies?
Yes, I think it makes sense to destroy the list and set ->owner = NULL. If we reset the owner, we can also avoid get_task_struct().
The only problem is perf_event_release_kernel(), it can race with the exiting event->owner. It can do get_task_struct() under rcu lock temporary, just to take the mutex and remove the entry.
> > And ptrace(), it doesn't use sys_perf_event_open() to create the event. > > Right, I guess it uses kernel based things, I guess we could not add > kernel based counters to the list.
Agreed, another case when event->owner should be NULL.
Hmm. With or without these changes. Shouldn't perf_event_release_kernel() remove the event from list before anything else? Otherwise, afaics a thread which does close(event_fd) can race with creator doing prctl(EVENTS_ENABLE), no?
Oleg.
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