Revert "blkdev: check for valid request queue before issuing flush"

This reverts commit f10d9f61.

We can't have queues without a make_request_fn any more (and the
loop device uses blk-mq these days anyway..).
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

block/blk-flush.c

@@ -454,15 +454,6 @@ int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
 	if (!q)
 		return -ENXIO;
 
-	/*
-	 * some block devices may not have their queue correctly set up here
-	 * (e.g. loop device without a backing file) and so issuing a flush
-	 * here will panic. Ensure there is a request function before issuing
-	 * the flush.
-	 */
-	if (!q->make_request_fn)
-		return -ENXIO;
-
 	bio = bio_alloc(gfp_mask, 0);
 	bio_set_dev(bio, bdev);
 	bio->bi_opf = REQ_OP_WRITE | REQ_PREFLUSH;