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Subject: Re: [PATCH] perf top: Fix a race in callchain handling
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Namhyung Kim <namhyung@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Paul Mackerras <paulus@samba.org>, Ingo Molnar <mingo@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Frederic Weisbecker <fweisbec@gmail.com>
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Date: Sat, 05 May 2012 20:22:47 +0200
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On Sun, 2012-05-06 at 00:23 +0900, Namhyung Kim wrote:
> +       static struct callchain_cursor cursor;

This just begs to become another concurrency problem. If anybody manages
to call multiple hists__collapse_insert_entry() concurrently you're
again up some creek without no paddle.

Adding global state is never a good option when dealing with
concurrency.