drbd: don't increase unacked_cnt when error is from resync write

In drbd_endio_write_sec_final(), if a write error has occured and the
protocol is not 'C', inc_unacked() will be called.

But when it is a resync write, we shouldn't increase unacked_cnt there
because of there is no corresponding dec_unacked(). If we do then
unacked_cnt will never be zero, which leads to the problem that in
do_start_resync(), start_resync_timer() will be scheduled over and over
again and the resync will never start.

Fix this problem by adding a condition in drbd_endio_write_sec_final().
When the error is from a resync write, don't increase unacked_cnt.

Signed-off-by: Rui Xu <rui.xu@easystack.cn>
Signed-off-by: Joel Colledge <joel.colledge@linbit.com>

drbd/drbd_sender.c

@@ -152,13 +152,16 @@ void drbd_endio_write_sec_final(struct drbd_peer_request *peer_req) __releases(l
 	block_id = peer_req->block_id;
 
 	if (peer_req->flags & EE_WAS_ERROR) {
-                /* In protocol != C, we usually do not send write acks.
-                 * In case of a write error, send the neg ack anyways. */
-                if (!__test_and_set_bit(__EE_SEND_WRITE_ACK, &peer_req->flags))
-                        inc_unacked(peer_device);
-                drbd_set_out_of_sync(peer_device, peer_req->i.sector, peer_req->i.size);
+		/* In protocol != C, we usually do not send write acks.
+		 * In case of a write error, send the neg ack anyways.
+		 * This only applies to to application writes, not to resync. */
+		if (block_id != ID_SYNCER) {
+			if (!__test_and_set_bit(__EE_SEND_WRITE_ACK, &peer_req->flags))
+				inc_unacked(peer_device);
+		}
+		drbd_set_out_of_sync(peer_device, peer_req->i.sector, peer_req->i.size);
 		drbd_handle_io_error(device, DRBD_WRITE_ERROR);
-        }
+	}
 
 	spin_lock_irqsave(&connection->peer_reqs_lock, flags);
 	device->writ_cnt += peer_req->i.size >> 9;