[PATCH V2 1/2] md/raid10: annotate lockless access to array_freeze_pending

[Zizhi Wo]

conf->array_freeze_pending is updated under conf->resync_lock in
freeze_array(), but read locklessly in allow_barrier(). Annotate these
accesses with READ_ONCE()/WRITE_ONCE() to document the intentional lockless
access and to prevent load/store tearing or fusing by the compiler. No
functional change.

Signed-off-by: Zizhi Wo <wozizhi@xxxxxxxxxx>
---
 drivers/md/raid10.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 0a3cfdd3f5df..dc40110a6736 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1031,11 +1031,11 @@ static bool wait_barrier(struct r10conf *conf, bool nowait)
 }
 
 static void allow_barrier(struct r10conf *conf)
 {
 	if ((atomic_dec_and_test(&conf->nr_pending)) ||
-			(conf->array_freeze_pending))
+	    READ_ONCE(conf->array_freeze_pending))
 		wake_up_barrier(conf);
 }
 
 static void freeze_array(struct r10conf *conf, int extra)
 {
@@ -1050,16 +1050,16 @@ static void freeze_array(struct r10conf *conf, int extra)
 	 * Thus the number queued (nr_queued) plus this request (extra)
 	 * must match the number of pending IOs (nr_pending) before
 	 * we continue.
 	 */
 	write_seqlock_irq(&conf->resync_lock);
-	conf->array_freeze_pending++;
+	WRITE_ONCE(conf->array_freeze_pending, conf->array_freeze_pending + 1);
 	WRITE_ONCE(conf->barrier, conf->barrier + 1);
 	conf->nr_waiting++;
 	wait_event_barrier_cmd(conf, atomic_read(&conf->nr_pending) ==
 			conf->nr_queued + extra, flush_pending_writes(conf));
-	conf->array_freeze_pending--;
+	WRITE_ONCE(conf->array_freeze_pending, conf->array_freeze_pending - 1);
 	write_sequnlock_irq(&conf->resync_lock);
 }
 
 static void unfreeze_array(struct r10conf *conf)
 {
-- 
2.52.0