linux-kernel - Re: [PATCH 1/3] perf: Rollback callchain buffer refcount under the callchain mutex

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Message-ID: <20130809102802.GC1045@krava.brq.redhat.com>
Date:	Fri, 9 Aug 2013 12:28:02 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 1/3] perf: Rollback callchain buffer refcount under the
 callchain mutex

On Fri, Aug 02, 2013 at 06:29:54PM +0200, Frederic Weisbecker wrote:
> When we fail to allocate the callchain buffers, we rollback the refcount
> we did and return from get_callchain_buffers().
> 
> However we take the refcount and allocate under the callchain lock
> but the rollback is done outside the lock.
> 
> As a result, while we rollback, some concurrent callchain user may
> call get_callchain_buffers(), see the non-zero refcount and give up
> because the buffers are NULL without itself retrying the allocation.
> 
> The consequences aren't that bad but that behaviour looks weird enough and
> it's better to give their chances to the following callchain users where
> we failed.
> 
> Reported-by: Jiri Olsa <jolsa@...hat.com>
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Jiri Olsa <jolsa@...hat.com>

Acked-by: Jiri Olsa <jolsa@...hat.com>
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