From 60b3df9c1e24a18aabb412da9905208c5f04ebea Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Fri, 13 Mar 2009 12:21:30 +0100
Subject: [PATCH] perf_counter: add comment to barrier
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>
---
arch/x86/kernel/cpu/perf_counter.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
index 1cedc3468ce5b..a2e3b76bfdc15 100644
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -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++) {
--
GitLab