Commit f3e3620f authored by Namhyung Kim's avatar Namhyung Kim Committed by Ingo Molnar
Browse files

locking/percpu-rwsem: Trigger contention tracepoints only if contended 



We mistakenly always fire lock contention tracepoints in the writer path,
while it should be conditional on the trylock result.

Signed-off-by: default avatarNamhyung Kim <namhyung@kernel.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarWaiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20231108215322.2845536-1-namhyung@kernel.org
parent f22f7132

kernel/locking/percpu-rwsem.c

+8 −3
Original line number Diff line number Diff line
@@ -223,9 +223,10 @@ static bool readers_active_check(struct percpu_rw_semaphore *sem) 


void __sched percpu_down_write(struct percpu_rw_semaphore *sem)

{

	bool contended = false;



	might_sleep();

	rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);

	trace_contention_begin(sem, LCB_F_PERCPU | LCB_F_WRITE);



	/* Notify readers to take the slow path. */

	rcu_sync_enter(&sem->rss);
@@ -234,8 +235,11 @@ void __sched percpu_down_write(struct percpu_rw_semaphore *sem) 
	 * Try set sem->block; this provides writer-writer exclusion.

	 * Having sem->block set makes new readers block.

	 */

	if (!__percpu_down_write_trylock(sem))

	if (!__percpu_down_write_trylock(sem)) {

		trace_contention_begin(sem, LCB_F_PERCPU | LCB_F_WRITE);

		percpu_rwsem_wait(sem, /* .reader = */ false);

		contended = true;

	}



	/* smp_mb() implied by __percpu_down_write_trylock() on success -- D matches A */
@@ -247,6 +251,7 @@ void __sched percpu_down_write(struct percpu_rw_semaphore *sem) 


	/* Wait for all active readers to complete. */

	rcuwait_wait_event(&sem->writer, readers_active_check(sem), TASK_UNINTERRUPTIBLE);

	if (contended)

		trace_contention_end(sem, 0);

}

EXPORT_SYMBOL_GPL(percpu_down_write);