From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Fri, 1 May 2009 10:23:16 +0000 (+0200)
Subject: perf_counter: fix race in perf_output_*
X-Git-Tag: v2.6.31-rc1~383^2~317
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c33a0bc4e41ef169d6e807d8abb9502544b518e5;p=pandora-kernel.git

perf_counter: fix race in perf_output_*

When two (or more) contexts output to the same buffer, it is possible
to observe half written output.

Suppose we have CPU0 doing perf_counter_mmap(), CPU1 doing
perf_counter_overflow(). If CPU1 does a wakeup and exposes head to
user-space, then CPU2 can observe the data CPU0 is still writing.

[ Impact: fix occasionally corrupted profiling records ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
LKML-Reference: <20090501102533.007821627@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---

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