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

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Message-ID: <20140714130237.GX9918@twins.programming.kicks-ass.net>
Date:	Mon, 14 Jul 2014 15:02:37 +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 01:43:59PM +0200, Jiri Olsa wrote:
> 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

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.

And I suppose install_exec_creds() already does the right thing when we
may not.

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