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Date:	Tue, 9 Nov 2010 17:58:05 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Prasad <prasad@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Q: perf_event && event->owner

On 11/09, Peter Zijlstra wrote:
>
> On Tue, 2010-11-09 at 16:57 +0100, Oleg Nesterov wrote:
> >
> > If the creator of perf_event dies, nobody can use its ->perf_event_list
> > anyway. What is the point to keep the reference to the dead task_struct
> > and preserve this ->perf_event_list?
>
> But when the owner dies it will close all its fds, which means it will
> clear its tsk->perf_event_list, no? (With exception of the case where
> the fd was passed through a unix-socket to another process).

fork(), pthread_create(). Only __fput() calls ->release, when the last
reference to file goes away.

And ptrace(), it doesn't use sys_perf_event_open() to create the event.

Oleg.

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