iser-target: Fix variable-length response error completion

commit 9253e667 upstream.

Since commit "2426bd45 target: Report correct response ..."
we might get a command with data_size that does not fit to
the number of allocated data sg elements. Given that we rely on
cmd t_data_nents which might be different than the data_size,
we sometimes receive local length error completion. The correct
approach would be to take the command data_size into account when
constructing the ib sg_list.
Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Jenny Falkovich <jennyf@mellanox.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/infiniband/ulp/isert/ib_isert.c

@@ -2487,7 +2487,6 @@ isert_build_rdma_wr(struct isert_conn *isert_conn, struct isert_cmd *isert_cmd,
 	page_off = offset % PAGE_SIZE;
 
 	send_wr->sg_list = ib_sge;
-	send_wr->num_sge = sg_nents;
 	send_wr->wr_id = (unsigned long)&isert_cmd->tx_desc;
 	/*
 	 * Perform mapping of TCM scatterlist memory ib_sge dma_addr.
@@ -2506,14 +2505,17 @@ isert_build_rdma_wr(struct isert_conn *isert_conn, struct isert_cmd *isert_cmd,
 			 ib_sge->addr, ib_sge->length, ib_sge->lkey);
 		page_off = 0;
 		data_left -= ib_sge->length;
+		if (!data_left)
+			break;
 		ib_sge++;
 		pr_debug("Incrementing ib_sge pointer to %p\n", ib_sge);
 	}
 
+	send_wr->num_sge = ++i;
 	pr_debug("Set outgoing sg_list: %p num_sg: %u from TCM SGLs\n",
 		 send_wr->sg_list, send_wr->num_sge);
 
-	return sg_nents;
+	return send_wr->num_sge;
 }
 
 static int