perf_counter: fix race in perf_output_*

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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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This commit is contained in:

Peter Zijlstra 2009-05-01 12:23:16 +02:00 • committed by Ingo Molnar

parent 3c56999eec

commit c33a0bc4e4

2 changed files with 105 additions and 30 deletions

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5

include/linux/perf_counter.h

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130

kernel/perf_counter.c

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