From: Peter Zijlstra Date: Fri, 13 Mar 2009 11:21:30 +0000 (+0100) Subject: perf_counter: add comment to barrier X-Git-Tag: firefly_0821_release~13973^2~481 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=60b3df9c1e24a18aabb412da9905208c5f04ebea;p=firefly-linux-kernel-4.4.55.git 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 Signed-off-by: Ingo Molnar --- diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c index 1cedc3468ce5..a2e3b76bfdc1 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++) {