block: Change elevator_init_mq() to always succeed

If the default elevator chosen is mq-deadline, elevator_init_mq() may
return an error if mq-deadline initialization fails, leading to
blk_mq_init_allocated_queue() returning an error, which in turn will
cause the block device initialization to fail and the device not being
exposed.

Instead of taking such extreme measure, handle mq-deadline
initialization failures in the same manner as when mq-deadline is not
available (no module to load), that is, default to the "none" scheduler.
With this change, elevator_init_mq() return type can be changed to void.

Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 12 insertions, 11 deletions

diff --git a/block/elevator.c b/block/elevator.c
index 4721834815bb..2944c129760c 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -628,34 +628,35 @@ static inline bool elv_support_iosched(struct request_queue *q)
 
 /*
  * For blk-mq devices supporting IO scheduling, we default to using mq-deadline,
- * if available, for single queue devices. If deadline isn't available OR we
- * have multiple queues, default to "none".
+ * if available, for single queue devices. If deadline isn't available OR
+ * deadline initialization fails OR we have multiple queues, default to "none".
  */
-int elevator_init_mq(struct request_queue *q)
+void elevator_init_mq(struct request_queue *q)
 {
 	struct elevator_type *e;
-	int err = 0;
+	int err;
 
 	if (!elv_support_iosched(q))
-		return 0;
+		return;
 
 	if (q->nr_hw_queues != 1)
-		return 0;
+		return;
 
 	WARN_ON_ONCE(test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags));
 
 	if (unlikely(q->elevator))
-		goto out;
+		return;
 
 	e = elevator_get(q, "mq-deadline", false);
 	if (!e)
-		goto out;
+		return;
 
 	err = blk_mq_init_sched(q, e);
-	if (err)
+	if (err) {
+		pr_warn("\"%s\" elevator initialization failed, "
+			"falling back to \"none\"\n", e->elevator_name);
 		elevator_put(e);
-out:
-	return err;
+	}
 }