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

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Message-ID: <20140714114359.GA17761@krava.redhat.com>
Date:	Mon, 14 Jul 2014 13:43:59 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
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 01:18:33PM +0200, Peter Zijlstra wrote:
> On Fri, Jul 11, 2014 at 01:56:19PM +0200, Jiri Olsa wrote:
> > From: Jiri Olsa <jolsa@...hat.com>
> > 
> > When task exits we close:
> >   1) all events that are installed in task
> >   2) all events owned by task (via file descriptor)
> > 
> > But we don't close children events of 2) events. Those children
> > events stay until the child task exits and are useless with the
> > parent being gone, because we have no way to get to values any
> > more.
> > 
> > Plus if the event stays installed in task even with the owner task
> > gone, it runs the perf callback any time the task forks, for no
> > real reason.
> > 
> > Closing all children events events when the owner task of the
> > parent event is closed.
> 
> Do we need this for the other patches, or is this an unrelated change? 

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

jirka
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