linux-kernel - Re: [PATCH] perf tools: enable close-on-exec flag on perf file descriptor

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Message-ID: <20140106163950.GP31570@twins.programming.kicks-ass.net>
Date:	Mon, 6 Jan 2014 17:39:50 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andi Kleen <ak@...ux.intel.com>
Cc:	Yann Droneaud <ydroneaud@...eya.com>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Stephane Eranian <eranian@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Michael Ellerman <michael@...erman.id.au>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf tools: enable close-on-exec flag on perf file
 descriptor

On Mon, Jan 06, 2014 at 08:27:54AM -0800, Andi Kleen wrote:
> On Mon, Jan 06, 2014 at 11:51:25AM +0100, Yann Droneaud wrote:
> > In a previous patch [1][2], flag PERF_FLAG_FD_CLOEXEC was
> > added to perf_event_open(2) syscall to allows userspace
> > to enable close-on-exec behavor atomically when creating
> > the file descriptor.
> > 
> > This patch makes perf tools use the new flag.
> 
> What is that good for? I can see why for a threaded program, but 
> "perf" is not threaded.

AFAICT its got nothing to do with threaded or not, but only with exec()
and we do in fact call exec() quite a lot in perf.

It ensures we do not leak open perf FDs into our child processes. Now
I'm not entirely sure how we do the exec these days but I think we were
good about not not leaking them anyway, but more paranoia never really
hurts.
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