fix review findings

controlplane/kubeadm/internal/controllers/controller.go

@@ -331,10 +331,10 @@ func (r *KubeadmControlPlaneReconciler) reconcile(ctx context.Context, cluster *
 
 	// Ensure all required labels exist on the controlled Machines.
 	// This logic is needed to add the `cluster.x-k8s.io/control-plane-name` label to Machines
-	// which were created before the `cluster.x-k8s.io/control-plane-name` label was introduced.
+	// which were created before the `cluster.x-k8s.io/control-plane-name` label was introduced
+	// or if a user manually removed the label.
 	// NOTE: Changes will be applied to the Machines in reconcileControlPlaneConditions.
 	// NOTE: cluster.x-k8s.io/control-plane is already set at this stage (it is used when reading controlPlane.Machines).
-	// TODO(sbueringer): Drop the following code with v1.4 after all existing Machines are guaranteed to have the new label.
 	for i := range controlPlane.Machines {
 		machine := controlPlane.Machines[i]
 		if value, ok := machine.Labels[clusterv1.MachineControlPlaneNameLabel]; !ok || value != kcp.Name {

internal/controllers/machinedeployment/machinedeployment_controller.go

@@ -231,8 +231,7 @@ func (r *Reconciler) reconcile(ctx context.Context, cluster *clusterv1.Cluster,
 	// Ensure all required labels exist on the controlled MachineSets.
 	// This logic is needed to add the `cluster.x-k8s.io/deployment-name` label to MachineSets
 	// which were created before the `cluster.x-k8s.io/deployment-name` label was added
-	// to all MachineSets created by a MachineDeployment.
-	// TODO(sbueringer): Drop the following code with v1.4 after all existing MachineSets are guaranteed to have the new label.
+	// to all MachineSets created by a MachineDeployment or if a user manually removed the label.
 	for idx := range msList {
 		machineSet := msList[idx]
 		if name, ok := machineSet.Labels[clusterv1.MachineDeploymentLabelName]; ok && name == d.Name {

internal/controllers/machineset/machineset_controller.go

@@ -293,10 +293,16 @@ func (r *Reconciler) reconcile(ctx context.Context, cluster *clusterv1.Cluster,
 	// Ensure all required labels exist on the controlled Machines.
 	// This logic is needed to add the `cluster.x-k8s.io/set-name` label to Machines
 	// which were created before the `cluster.x-k8s.io/set-name` label was added to
-	// all Machines created by a MachineSet.
-	// TODO(sbueringer): Drop the following code with v1.4 after all existing Machines are guaranteed to have the new label.
+	// all Machines created by a MachineSet or if a user manually removed the label.
 	for _, machine := range filteredMachines {
-		if name, ok := machine.Labels[clusterv1.MachineSetLabelName]; ok && name == machineSet.Name {
+		mdNameOnMachineSet, mdNameSetOnMachineSet := machineSet.Labels[clusterv1.MachineDeploymentLabelName]
+		mdNameOnMachine := machine.Labels[clusterv1.MachineDeploymentLabelName]
+
+		if msName, ok := machine.Labels[clusterv1.MachineSetLabelName]; ok && msName == machineSet.Name &&
+			(!mdNameSetOnMachineSet || mdNameOnMachineSet == mdNameOnMachine) {
+			// Continue if the MachineSet name label is already set correctly and
+			// either the MachineDeployment name label is not set on the MachineSet or
+			// the MachineDeployment name label is set correctly on the Machine.
 			continue
 		}
 
@@ -305,9 +311,9 @@ func (r *Reconciler) reconcile(ctx context.Context, cluster *clusterv1.Cluster,
 			return ctrl.Result{}, errors.Wrapf(err, "failed to apply %s label to Machine %q", clusterv1.MachineSetLabelName, machine.Name)
 		}
 		machine.Labels[clusterv1.MachineSetLabelName] = machineSet.Name
-		// Propagate the MachineDeploymentLabelName from MachineSet to Machine if it exists.
-		if mdName, ok := machineSet.Labels[clusterv1.MachineDeploymentLabelName]; ok {
-			machine.Labels[clusterv1.MachineDeploymentLabelName] = mdName
+		// Propagate the MachineDeploymentLabelName from MachineSet to Machine if it is set on the MachineSet.
+		if mdNameSetOnMachineSet {
+			machine.Labels[clusterv1.MachineDeploymentLabelName] = mdNameOnMachineSet
 		}
 		if err := helper.Patch(ctx, machine); err != nil {
 			return ctrl.Result{}, errors.Wrapf(err, "failed to apply %s label to Machine %q", clusterv1.MachineSetLabelName, machine.Name)