releases/5.1.6/sbitmap-fix-improper-use-of-smp_mb__before_atomic.patch

From a0934fd2b1208458e55fc4b48f55889809fce666 Mon Sep 17 00:00:00 2001
From: Andrea Parri <andrea.parri@amarulasolutions.com>
Date: Mon, 20 May 2019 19:23:57 +0200
Subject: sbitmap: fix improper use of smp_mb__before_atomic()

From: Andrea Parri <andrea.parri@amarulasolutions.com>

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")
Cc: stable@vger.kernel.org
Reported-by: "Paul E. McKenney" <paulmck@linux.ibm.com>
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Omar Sandoval <osandov@fb.com>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: linux-block@vger.kernel.org
Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 lib/sbitmap.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -435,7 +435,7 @@ static void sbitmap_queue_update_wake_ba
 		 * to ensure that the batch size is updated before the wait
 		 * counts.
 		 */
-		smp_mb__before_atomic();
+		smp_mb();
 		for (i = 0; i < SBQ_WAIT_QUEUES; i++)
 			atomic_set(&sbq->ws[i].wait_cnt, 1);
 	}