block: shortcut __submit_bio_noacct for blk-mq drivers

For blk-mq drivers bios can only be inserted for the same queue.  So
bypass the complicated sorting logic in __submit_bio_noacct with
a blk-mq simpler submission helper.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-core.c

@@ -1152,6 +1152,34 @@ static blk_qc_t __submit_bio_noacct(struct bio *bio)
 	return ret;
 }
 
+static blk_qc_t __submit_bio_noacct_mq(struct bio *bio)
+{
+	struct gendisk *disk = bio->bi_disk;
+	struct bio_list bio_list;
+	blk_qc_t ret = BLK_QC_T_NONE;
+
+	bio_list_init(&bio_list);
+	current->bio_list = &bio_list;
+
+	do {
+		WARN_ON_ONCE(bio->bi_disk != disk);
+
+		if (unlikely(bio_queue_enter(bio) != 0))
+			continue;
+
+		if (!blk_crypto_bio_prep(&bio)) {
+			blk_queue_exit(disk->queue);
+			ret = BLK_QC_T_NONE;
+			continue;
+		}
+
+		ret = blk_mq_submit_bio(bio);
+	} while ((bio = bio_list_pop(&bio_list)));
+
+	current->bio_list = NULL;
+	return ret;
+}
+
 /**
  * submit_bio_noacct - re-submit a bio to the block device layer for I/O
  * @bio:  The bio describing the location in memory and on the device.
@@ -1177,6 +1205,8 @@ blk_qc_t submit_bio_noacct(struct bio *bio)
 		return BLK_QC_T_NONE;
 	}
 
+	if (!bio->bi_disk->fops->submit_bio)
+		return __submit_bio_noacct_mq(bio);
 	return __submit_bio_noacct(bio);
 }
 EXPORT_SYMBOL(submit_bio_noacct);