linux-kernel - Re: [PATCH 2/5] perf: Destroy event's children on task exit

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Message-ID: <20140714133542.GZ9918@twins.programming.kicks-ass.net>
Date:	Mon, 14 Jul 2014 15:35:42 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Jiri Olsa <jolsa@...nel.org>, linux-kernel@...r.kernel.org,
	Alexander Yarygin <yarygin@...ux.vnet.ibm.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH 2/5] perf: Destroy event's children on task exit

On Mon, Jul 14, 2014 at 03:22:23PM +0200, Jiri Olsa wrote:
> > > if we dont do it, the event stays installed without owner and
> > > perf fork callback will be called and fail on permission checking
> > > (because of owner == NULL) ... so yes, I think it's needed
> > 
> > Oh, right. Alternatively, we don't need permission checking for inherits
> > at all, if we're allowed to create the initial event, we should be good
> > for inherits.
> 
> I could adress that in follow up patch.. or you want this instead
> of this one? IMO we should close those events anyway..

I tend to agree that closing them all is nicer. But we need to be
careful while doing it so as not to make the clone/fork path block on
it.

I _think_ it might be best to separate these two issues for the moment,
so cure the reported problem by avoiding the permission check for
inherited events -- IFF you agree with the previous argument that
install_exec_creds() should be sufficient.

And then so a patch playing games with perf_event_init_context()
(clone/fork) vs perf_event_exit_task() (exit).



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