[PATCH 3.16 22/87] sbitmap: fix improper use of smp_mb__before_atomic()

3.16.75-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Andrea Parri <redacted>

commit a0934fd2b1208458e55fc4b48f55889809fce666 upstream.

This barrier only applies to the read-modify-write operations; in
particular, it does not apply to the atomic_set() primitive.

Replace the barrier with an smp_mb().

Fixes: 6c0ca7ae292ad ("sbitmap: fix wakeup hang after sbq resize")
Reported-by: "Paul E. McKenney" <redacted>
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrea Parri <redacted>
Reviewed-by: Ming Lei <redacted>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Omar Sandoval <redacted>
Cc: Ming Lei <redacted>
Cc: linux-block@vger.kernel.org
Cc: "Paul E. McKenney" <redacted>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <redacted>
---
 block/blk-mq-tag.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c

@@ -499,7 +499,7 @@ static void bt_update_count(struct blk_m
 		 * Pairs with the memory barrier in bt_clear_tag() to ensure
 		 * that the batch size is updated before the wait counts.
 		 */
-		smp_mb__before_atomic();
+		smp_mb();
 		for (i = 0; i < BT_WAIT_QUEUES; i++)
 			atomic_set(&bt->bs[i].wait_cnt, 1);
 	}