Re: Q: perf_event && event->owner

[Oleg Nesterov]

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.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/