linux-kernel - Re: [PATCH 2/8] perf: Sanitize get_callchain

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Message-ID: <20130801135757.GF431@somewhere>
Date:	Thu, 1 Aug 2013 15:57:59 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 2/8] perf: Sanitize get_callchain_buffer()

On Thu, Aug 01, 2013 at 03:54:01PM +0200, Jiri Olsa wrote:
> On Thu, Aug 01, 2013 at 03:49:36PM +0200, Frederic Weisbecker wrote:
> > On Thu, Aug 01, 2013 at 03:32:17PM +0200, Jiri Olsa wrote:
> > > On Thu, Aug 01, 2013 at 03:28:34PM +0200, Frederic Weisbecker wrote:
> > > 
> > > SNIP
> > > 
> > > > > also for following case:
> > > > > 
> > > > >         count = atomic_inc_return(&nr_callchain_events);
> > > > >         if (WARN_ON_ONCE(count < 1)) {
> > > > >                 err = -EINVAL;
> > > > >                 goto exit;
> > > > >         }
> > > > > 
> > > > > seems like it screws the count
> > > > 
> > > > I'm not sure what you mean here. You mean that it could be negative when the dec is done
> > > > outside the lock?
> > > 
> > > yes
> > > 
> > 
> > I don't understand why.
> 
> ah ok, with the count being 0 the nr_callchain_events still
> increments right? then it's ok..

Yep. But I still need to move the dec into the lock though.

Thanks for catching this!
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