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.shish...@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
