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perf_counter: add comment to barrier

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We need to ensure the enabled=0 write happens before we
start disabling the actual counters, so that a pcm_amd_enable()
will not enable one underneath us.

I think the race is impossible anyway, we always balance the
ops within any one context and perform enable() with IRQs disabled.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2009-03-13 12:21:30 +01:00 committed by Ingo Molnar
parent 755642322a
commit 60b3df9c1e
1 changed files with 4 additions and 0 deletions
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4
arch/x86/kernel/cpu/perf_counter.c
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@ -247,6 +247,10 @@ static u64 pmc_amd_save_disable_all(void)
enabled = cpuc->enabled;
cpuc->enabled = 0;
/*
* ensure we write the disable before we start disabling the
* counters proper, so that pcm_amd_enable() does the right thing.
*/
barrier();
for (idx = 0; idx < nr_counters_generic; idx++) {