dm: remove request-based DM queue's lld_busy_fn hook

DM multipath is the only caller of blk_lld_busy() -- which calls a
queue's lld_busy_fn hook.  Request-based DM doesn't support stacking
multipath devices so there is no reason to register the lld_busy_fn hook
on a multipath device's queue using blk_queue_lld_busy().

As such, remove functions dm_lld_busy and dm_table_any_busy_target.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm.c

@@ -2006,22 +2006,6 @@ out:
 	dm_put_live_table(md, srcu_idx);
 }
 
-static int dm_lld_busy(struct request_queue *q)
-{
-	int r;
-	struct mapped_device *md = q->queuedata;
-	struct dm_table *map = dm_get_live_table_fast(md);
-
-	if (!map || test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags))
-		r = 1;
-	else
-		r = dm_table_any_busy_target(map);
-
-	dm_put_live_table_fast(md);
-
-	return r;
-}
-
 static int dm_any_congested(void *congested_data, int bdi_bits)
 {
 	int r = bdi_bits;
@@ -2545,7 +2529,6 @@ static int dm_init_request_based_queue(struct mapped_device *md)
 	dm_init_md_queue(md);
 	blk_queue_softirq_done(md->queue, dm_softirq_done);
 	blk_queue_prep_rq(md->queue, dm_prep_fn);
-	blk_queue_lld_busy(md->queue, dm_lld_busy);
 
 	/* Also initialize the request-based DM worker thread */
 	init_kthread_worker(&md->kworker);