Commit 5bce9db1 authored Aug 29, 2017 by Alexander Shishkin Committed by Ingo Molnar Sep 29, 2017

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: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Peter 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.com

Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 4c4de7d3

kernel/events/core.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -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;

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