From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Mon, 6 Apr 2009 09:44:59 +0000 (+0200)
Subject: perf_counter: update mmap() counter read, take 2
X-Git-Tag: v2.6.31-rc1~383^2~407
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a2e87d06ddbe6e6fdb8d6d2e5e985efe4efb07dd;p=pandora-kernel.git

perf_counter: update mmap() counter read, take 2

Update the userspace read method.

Paul noted that:
 - userspace cannot observe ->lock & 1 on the same cpu.
 - we need a barrier() between reading ->lock and ->index
   to ensure we read them in that prticular order.

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: <20090406094517.368446033@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---

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