xen-blkback: bio_alloc can't fail if it is allow to sleep

Remove handling of NULL returns from sleeping bio_alloc calls given that
those can't fail.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220124091107.642561-13-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/xen-blkback/blkback.c

@@ -1327,9 +1327,6 @@ static int dispatch_rw_block_io(struct xen_blkif_ring *ring,
 				     seg[i].nsec << 9,
 				     seg[i].offset) == 0)) {
 			bio = bio_alloc(GFP_KERNEL, bio_max_segs(nseg - i));
-			if (unlikely(bio == NULL))
-				goto fail_put_bio;
-
 			biolist[nbio++] = bio;
 			bio_set_dev(bio, preq.bdev);
 			bio->bi_private = pending_req;
@@ -1346,9 +1343,6 @@ static int dispatch_rw_block_io(struct xen_blkif_ring *ring,
 		BUG_ON(operation_flags != REQ_PREFLUSH);
 
 		bio = bio_alloc(GFP_KERNEL, 0);
-		if (unlikely(bio == NULL))
-			goto fail_put_bio;
-
 		biolist[nbio++] = bio;
 		bio_set_dev(bio, preq.bdev);
 		bio->bi_private = pending_req;
@@ -1381,14 +1375,6 @@ static int dispatch_rw_block_io(struct xen_blkif_ring *ring,
 	free_req(ring, pending_req);
 	msleep(1); /* back off a bit */
 	return -EIO;
-
- fail_put_bio:
-	for (i = 0; i < nbio; i++)
-		bio_put(biolist[i]);
-	atomic_set(&pending_req->pendcnt, 1);
-	__end_block_io_op(pending_req, BLK_STS_RESOURCE);
-	msleep(1); /* back off a bit */
-	return -EIO;
 }