block: remove redundant explicit memory barrier from rq_qos waiter and waker

The memory barriers in list_del_init_careful() and list_empty_careful()
in pairs already handle the proper ordering between data.got_token
and data.wq.entry. So remove the redundant explicit barriers. And also
change a "break" statement to "return" to avoid redundant calling of
finish_wait().

Signed-off-by: Muchun Song <[email protected]>
Reviewed-by: Chengming Zhou <[email protected]>
Reviewed-by: Omar Sandoval <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: Muchun Song

block/blk-rq-qos.c

@@ -218,7 +218,6 @@ static int rq_qos_wake_function(struct wait_queue_entry *curr,
 		return -1;
 
 	data->got_token = true;
-	smp_wmb();
 	wake_up_process(data->task);
 	list_del_init_careful(&curr->entry);
 	return 1;
@@ -274,10 +273,9 @@ void rq_qos_wait(struct rq_wait *rqw, void *private_data,
 			 * which means we now have two. Put our local token
 			 * and wake anyone else potentially waiting for one.
 			 */
-			smp_rmb();
 			if (data.got_token)
 				cleanup_cb(rqw, private_data);
-			break;
+			return;
 		}
 		io_schedule();
 		has_sleeper = true;