drbd: do not attempt to start resync if we receive bitmap twice

We expect to only receive the bitmap once in a bitmap exchange. In the
situation described in the recent commit "drbd: use mod_timer() instead
of add_timer() for starting resync", the peer breaks this assumption.
This change protects us against this unexpected behavior of our peer.

drbd/drbd_receiver.c

@@ -7858,7 +7858,10 @@ static int receive_bitmap(struct drbd_connection *connection, struct packet_info
 
 	drbd_bm_slot_unlock(peer_device);
 
-	if (repl_state == L_WF_BITMAP_S) {
+	if (test_bit(B_RS_H_DONE, &peer_device->flags)) {
+		/* We have entered drbd_start_resync() since starting the bitmap exchange. */
+		drbd_warn(peer_device, "Received bitmap more than once; ignoring\n");
+	} else if (repl_state == L_WF_BITMAP_S) {
 		drbd_start_resync(peer_device, L_SYNC_SOURCE);
 	} else if (repl_state == L_WF_BITMAP_T) {
 		if (connection->agreed_pro_version < 110) {

drbd/drbd_state.c

@@ -2553,6 +2553,14 @@ static void finish_state_change(struct drbd_resource *resource)
 			if (did != should)
 				start_new_epoch = true;
 
+			if (peer_device->repl_state[OLD] != L_WF_BITMAP_S &&
+					peer_device->repl_state[NEW] == L_WF_BITMAP_S)
+				clear_bit(B_RS_H_DONE, &peer_device->flags);
+
+			if (peer_device->repl_state[OLD] != L_WF_BITMAP_T &&
+					peer_device->repl_state[NEW] == L_WF_BITMAP_T)
+				clear_bit(B_RS_H_DONE, &peer_device->flags);
+
 			if (!is_sync_state(peer_device, NOW) &&
 			    is_sync_state(peer_device, NEW)) {
 				clear_bit(RS_DONE, &peer_device->flags);