making sure fresh state works before turning off query service during a split

Signed-off-by: Yufei Chen <yufei@squareup.com>

go/vt/wrangler/keyspace.go

@@ -641,11 +641,22 @@ func (wr *Wrangler) masterMigrateServedType(ctx context.Context, keyspace string
 	}()
 
 	// Phase 1
+	// - check topology service can successfully refresh both source and target master
 	// - switch the source shards to read-only by disabling query service
 	// - gather all replication points
 	// - wait for filtered replication to catch up
 	// - mark source shards as frozen
 	event.DispatchUpdate(ev, "disabling query service on all source masters")
+	// making sure the refreshMaster on both source and target are working before turning off query service on source
+	if err := wr.refreshMasters(ctx, sourceShards); err != nil {
+		wr.cancelMasterMigrateServedTypes(ctx, keyspace, sourceShards)
+		return err
+	}
+	if err := wr.refreshMasters(ctx, destinationShards); err != nil {
+		wr.cancelMasterMigrateServedTypes(ctx, keyspace, sourceShards)
+		return err
+	}
+
 	if err := wr.updateShardRecords(ctx, keyspace, sourceShards, nil, topodatapb.TabletType_MASTER, true, false); err != nil {
 		wr.cancelMasterMigrateServedTypes(ctx, keyspace, sourceShards)
 		return err