dm: allocate blk_mq_tag_set rather than embed in mapped_device

The blk_mq_tag_set is only needed for dm-mq support.  There is point
wasting space in 'struct mapped_device' for non-dm-mq devices.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> # check kzalloc return

drivers/md/dm.c

@@ -223,7 +223,7 @@ struct mapped_device {
 	ktime_t last_rq_start_time;
 
 	/* for blk-mq request-based DM support */
-	struct blk_mq_tag_set tag_set;
+	struct blk_mq_tag_set *tag_set;
 	bool use_blk_mq;
 };
 
@@ -2388,8 +2388,10 @@ static void free_dev(struct mapped_device *md)
 	unlock_fs(md);
 
 	cleanup_mapped_device(md);
-	if (md->use_blk_mq)
-		blk_mq_free_tag_set(&md->tag_set);
+	if (md->tag_set) {
+		blk_mq_free_tag_set(md->tag_set);
+		kfree(md->tag_set);
+	}
 
 	free_table_devices(&md->table_devices);
 	dm_stats_cleanup(&md->stats);
@@ -2710,24 +2712,28 @@ static int dm_init_request_based_blk_mq_queue(struct mapped_device *md)
 	struct request_queue *q;
 	int err;
 
-	memset(&md->tag_set, 0, sizeof(md->tag_set));
-	md->tag_set.ops = &dm_mq_ops;
-	md->tag_set.queue_depth = dm_get_blk_mq_queue_depth();
-	md->tag_set.numa_node = NUMA_NO_NODE;
-	md->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
-	md->tag_set.nr_hw_queues = dm_get_blk_mq_nr_hw_queues();
+	md->tag_set = kzalloc(sizeof(struct blk_mq_tag_set), GFP_KERNEL);
+	if (!md->tag_set)
+		return -ENOMEM;
+
+	md->tag_set->ops = &dm_mq_ops;
+	md->tag_set->queue_depth = dm_get_blk_mq_queue_depth();
+	md->tag_set->numa_node = NUMA_NO_NODE;
+	md->tag_set->flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
+	md->tag_set->nr_hw_queues = dm_get_blk_mq_nr_hw_queues();
+	md->tag_set->driver_data = md;
+
+	md->tag_set->cmd_size = sizeof(struct dm_rq_target_io);
 	if (md_type == DM_TYPE_REQUEST_BASED) {
-		/* make the memory for non-blk-mq clone part of the pdu */
-		md->tag_set.cmd_size = sizeof(struct dm_rq_target_io) + sizeof(struct request);
-	} else
-		md->tag_set.cmd_size = sizeof(struct dm_rq_target_io);
-	md->tag_set.driver_data = md;
+		/* put the memory for non-blk-mq clone at the end of the pdu */
+		md->tag_set->cmd_size += sizeof(struct request);
+	}
 
-	err = blk_mq_alloc_tag_set(&md->tag_set);
+	err = blk_mq_alloc_tag_set(md->tag_set);
 	if (err)
-		return err;
+		goto out_kfree_tag_set;
 
-	q = blk_mq_init_allocated_queue(&md->tag_set, md->queue);
+	q = blk_mq_init_allocated_queue(md->tag_set, md->queue);
 	if (IS_ERR(q)) {
 		err = PTR_ERR(q);
 		goto out_tag_set;
@@ -2744,7 +2750,10 @@ static int dm_init_request_based_blk_mq_queue(struct mapped_device *md)
 	return 0;
 
 out_tag_set:
-	blk_mq_free_tag_set(&md->tag_set);
+	blk_mq_free_tag_set(md->tag_set);
+out_kfree_tag_set:
+	kfree(md->tag_set);
+
 	return err;
 }