block: handle partial completions for special payload requests

SCSI devices can return short writes on Write Same just like for normal
writes, so we need to handle this case for our special payload requests
as well.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: Abdul Haleem <abdhalee@linux.vnet.ibm.com>
Tested-by: Abdul Haleem <abdhalee@linux.vnet.ibm.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/blk-core.c

@@ -2644,8 +2644,6 @@ bool blk_update_request(struct request *req, int error, unsigned int nr_bytes)
 		return false;
 	}
 
-	WARN_ON_ONCE(req->rq_flags & RQF_SPECIAL_PAYLOAD);
-
 	req->__data_len -= total_bytes;
 
 	/* update sector only for requests with clear definition of sector */
@@ -2658,6 +2656,7 @@ bool blk_update_request(struct request *req, int error, unsigned int nr_bytes)
 		req->cmd_flags |= req->bio->bi_opf & REQ_FAILFAST_MASK;
 	}
 
+	if (!(req->rq_flags & RQF_SPECIAL_PAYLOAD)) {
 		/*
 		 * If total number of sectors is less than the first segment
 		 * size, something has gone terribly wrong.
@@ -2669,6 +2668,7 @@ bool blk_update_request(struct request *req, int error, unsigned int nr_bytes)
 
 		/* recalculate the number of segments */
 		blk_recalc_rq_segments(req);
+	}
 
 	return true;
 }