scsi: use blk_rq_payload_bytes

Without that we'll pass a wrong payload size in cmd->sdb, which
can lead to hangs with drivers that need the total transfer size.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: Chris Valean <v-chvale@microsoft.com>
Reported-by: Dexuan Cui <decui@microsoft.com>
Fixes: f9d03f9 ("block: improve handling of the magic discard payload")
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/scsi/scsi_lib.c

@@ -1018,7 +1018,7 @@ static int scsi_init_sgtable(struct request *req, struct scsi_data_buffer *sdb)
 	count = blk_rq_map_sg(req->q, req, sdb->table.sgl);
 	BUG_ON(count > sdb->table.nents);
 	sdb->table.nents = count;
-	sdb->length = blk_rq_bytes(req);
+	sdb->length = blk_rq_payload_bytes(req);
 	return BLKPREP_OK;
 }