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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: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20231108215322.2845536-1-namhyung@kernel.org
This commit is contained in:
Namhyung Kim 2023-11-08 13:53:22 -08:00 committed by Ingo Molnar
parent f22f71322a
commit f3e3620f1a
1 changed files with 8 additions and 3 deletions
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11
kernel/locking/percpu-rwsem.c
View File

@ -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 */
@ -247,7 +251,8 @@ 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);
trace_contention_end(sem, 0);
if (contended)
trace_contention_end(sem, 0);
}
EXPORT_SYMBOL_GPL(percpu_down_write);