[PATCH 4.9 47/52] dm bufio: dont take the lock in dm_bufio_shrink_count

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mikulas Patocka <mpatocka@xxxxxxxxxx>

commit d12067f428c037b4575aaeb2be00847fc214c24a upstream.

dm_bufio_shrink_count() is called from do_shrink_slab to find out how many
freeable objects are there. The reported value doesn't have to be precise,
so we don't need to take the dm-bufio lock.

Suggested-by: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/md/dm-bufio.c |   16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -1598,19 +1598,11 @@ dm_bufio_shrink_scan(struct shrinker *sh
 static unsigned long
 dm_bufio_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
 {
-	struct dm_bufio_client *c;
-	unsigned long count;
-	unsigned long retain_target;
+	struct dm_bufio_client *c = container_of(shrink, struct dm_bufio_client, shrinker);
+	unsigned long count = READ_ONCE(c->n_buffers[LIST_CLEAN]) +
+			      READ_ONCE(c->n_buffers[LIST_DIRTY]);
+	unsigned long retain_target = get_retain_buffers(c);
 
-	c = container_of(shrink, struct dm_bufio_client, shrinker);
-	if (sc->gfp_mask & __GFP_FS)
-		dm_bufio_lock(c);
-	else if (!dm_bufio_trylock(c))
-		return 0;
-
-	count = c->n_buffers[LIST_CLEAN] + c->n_buffers[LIST_DIRTY];
-	retain_target = get_retain_buffers(c);
-	dm_bufio_unlock(c);
 	return (count < retain_target) ? 0 : (count - retain_target);
 }