block: require blk_rq_prep_clone() be given an initialized clone request

Prepare to allow blk_rq_prep_clone() to accept clone requests that were
allocated from blk-mq request queues.  As such the blk_rq_prep_clone()
caller must first initialize the clone request.
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/blk-core.c

@@ -2945,8 +2945,6 @@ int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
 	if (!bs)
 		bs = fs_bio_set;
 
-	blk_rq_init(NULL, rq);
-
 	__rq_for_each_bio(bio_src, rq_src) {
 		bio = bio_clone_fast(bio_src, gfp_mask, bs);
 		if (!bio)

drivers/md/dm.c

@@ -1719,6 +1719,7 @@ static int setup_clone(struct request *clone, struct request *rq,
 {
 	int r;
 
+	blk_rq_init(NULL, rq);
 	r = blk_rq_prep_clone(clone, rq, tio->md->bs, GFP_ATOMIC,
 			      dm_rq_bio_constructor, tio);
 	if (r)