Commit 5bce9db1 authored by Alexander Shishkin's avatar Alexander Shishkin Committed by Ingo Molnar

perf/core: Explain perf_sched_mutex

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 a short explanation.
Signed-off-by: default avatarAlexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170829140103.6563-1-alexander.shishkin@linux.intel.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 4c4de7d3
......@@ -9394,6 +9394,11 @@ 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;
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment