block: use lock bitops for the tag map.

The block queue tag map can use lock bitops.
Signed-off-by: NNick Piggin <npiggin@suse.de>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>

block/ll_rw_blk.c

@@ -1057,18 +1057,16 @@ void blk_queue_end_tag(struct request_queue *q, struct request *rq)
 
 	bqt->tag_index[tag] = NULL;
 
-	/*
-	 * We use test_and_clear_bit's memory ordering properties here.
-	 * The tag_map bit acts as a lock for tag_index[bit], so we need
-	 * a barrer before clearing the bit (precisely: release semantics).
-	 * Could use clear_bit_unlock when it is merged.
-	 */
-	if (unlikely(!test_and_clear_bit(tag, bqt->tag_map))) {
+	if (unlikely(!test_bit(tag, bqt->tag_map))) {
 		printk(KERN_ERR "%s: attempt to clear non-busy tag (%d)\n",
 		       __FUNCTION__, tag);
 		return;
 	}
-
+	/*
+	 * The tag_map bit acts as a lock for tag_index[bit], so we need
+	 * unlock memory barrier semantics.
+	 */
+	clear_bit_unlock(tag, bqt->tag_map);
 	bqt->busy--;
 }
 
@@ -1114,10 +1112,10 @@ int blk_queue_start_tag(struct request_queue *q, struct request *rq)
 		if (tag >= bqt->max_depth)
 			return 1;
 
-	} while (test_and_set_bit(tag, bqt->tag_map));
+	} while (test_and_set_bit_lock(tag, bqt->tag_map));
 	/*
-	 * We rely on test_and_set_bit providing lock memory ordering semantics
-	 * (could use test_and_set_bit_lock when it is merged).
+	 * We need lock ordering semantics given by test_and_set_bit_lock.
+	 * See blk_queue_end_tag for details.
 	 */
 
 	rq->cmd_flags |= REQ_QUEUED;