perf_counter: update mmap() counter read, take 2
authorPeter Zijlstra <a.p.zijlstra@chello.nl>
Mon, 6 Apr 2009 09:44:59 +0000 (11:44 +0200)
committerIngo Molnar <mingo@elte.hu>
Tue, 7 Apr 2009 08:48:54 +0000 (10:48 +0200)
commita2e87d06ddbe6e6fdb8d6d2e5e985efe4efb07dd
treeaf0fdeb24c4e957d4e87a50ba358e5fdba6f7600
parent92f22a3865abe87eea2609a6f8e5be5123f7ce4f
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>
include/linux/perf_counter.h