Messages in this thread Patch in this message |  | | From | Alexander Shishkin <> | Subject | [PATCH] perf: Explain perf_sched_mutex | Date | Tue, 29 Aug 2017 17:01:03 +0300 |
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To clarify why atomic_inc_return(&perf_sched_events) is not sufficient and a mutex is needed to order static branch enabling vs the atomic counter increment, this adds a comment with an short explanation.
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com> --- kernel/events/core.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/kernel/events/core.c b/kernel/events/core.c index efe09b8c38..2c8719b635 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -9569,6 +9569,11 @@ static void account_event(struct perf_event *event) inc = true; if (inc) { + /* + * We need the mutex here because static_branch_enable() + * must complete *before* the perf_sched_count increment + * becomes visible. + */ if (atomic_inc_not_zero(&perf_sched_count)) goto enabled; -- 2.14.1
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