The following commit has been merged into the locking/core branch of tip:
Commit-ID: f3e3620f1a97fcd02a5f3606fa63888dbcffd82c
Gitweb: https://git.kernel.org/tip/f3e3620f1a97fcd02a5f3606fa63888dbcffd82c
Author: Namhyung Kim <namhyung@xxxxxxxxxx>
AuthorDate: Wed, 08 Nov 2023 13:53:22 -08:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Wed, 28 Feb 2024 13:10:29 +01:00
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@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Reviewed-by: Waiman Long <longman@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20231108215322.2845536-1-namhyung@xxxxxxxxxx
---
kernel/locking/percpu-rwsem.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index 185bd1c..6083883 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -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);
|