DRA kubelet: fix potential flake in unit test

If the test binary ran long enough after test completion to reach the
ResourceSlice removal grace period, that background activity started and failed
because it was using out-dated state and an invalid testing.T pointer, causing
a panic.

The root cause was to leave those background activities running. They need to
be stopped before a test returns.

pkg/kubelet/cm/dra/plugin/registration.go

@@ -52,10 +52,12 @@ type RegistrationHandler struct {
 	// This is necessary because it implements APIs which don't
 	// provide a context.
 	backgroundCtx context.Context
+	cancel        func(err error)
 	kubeClient    kubernetes.Interface
 	getNode       func() (*v1.Node, error)
 	wipingDelay   time.Duration
 
+	wg    sync.WaitGroup
 	mutex sync.Mutex
 
 	// pendingWipes maps a plugin name to a cancel function for
@@ -76,9 +78,15 @@ var _ cache.PluginHandler = &RegistrationHandler{}
 // If a kubeClient is provided, then it synchronizes ResourceSlices
 // with the resource information provided by plugins.
 func NewRegistrationHandler(kubeClient kubernetes.Interface, getNode func() (*v1.Node, error), wipingDelay time.Duration) *RegistrationHandler {
+	// The context and thus logger should come from the caller.
+	return newRegistrationHandler(context.TODO(), kubeClient, getNode, wipingDelay)
+}
+
+func newRegistrationHandler(ctx context.Context, kubeClient kubernetes.Interface, getNode func() (*v1.Node, error), wipingDelay time.Duration) *RegistrationHandler {
+	ctx, cancel := context.WithCancelCause(ctx)
 	handler := &RegistrationHandler{
-		// The context and thus logger should come from the caller.
-		backgroundCtx: klog.NewContext(context.TODO(), klog.LoggerWithName(klog.TODO(), "DRA registration handler")),
+		backgroundCtx: klog.NewContext(ctx, klog.LoggerWithName(klog.FromContext(ctx), "DRA registration handler")),
+		cancel:        cancel,
 		kubeClient:    kubeClient,
 		getNode:       getNode,
 		wipingDelay:   wipingDelay,
@@ -92,13 +100,24 @@ func NewRegistrationHandler(kubeClient kubernetes.Interface, getNode func() (*v1
 	// to start up.
 	//
 	// This has to run in the background.
-	logger := klog.LoggerWithName(klog.FromContext(handler.backgroundCtx), "startup")
-	ctx := klog.NewContext(handler.backgroundCtx, logger)
-	go handler.wipeResourceSlices(ctx, 0 /* no delay */, "" /* all drivers */)
+	handler.wg.Add(1)
+	go func() {
+		defer handler.wg.Done()
+
+		logger := klog.LoggerWithName(klog.FromContext(handler.backgroundCtx), "startup")
+		ctx := klog.NewContext(handler.backgroundCtx, logger)
+		handler.wipeResourceSlices(ctx, 0 /* no delay */, "" /* all drivers */)
+	}()
 
 	return handler
 }
 
+// Stop cancels any remaining background activities and blocks until all goroutines have stopped.
+func (h *RegistrationHandler) Stop() {
+	h.cancel(errors.New("Stop was called"))
+	h.wg.Wait()
+}
+
 // wipeResourceSlices deletes ResourceSlices of the node, optionally just for a specific driver.
 // Wiping will delay for a while and can be canceled by canceling the context.
 func (h *RegistrationHandler) wipeResourceSlices(ctx context.Context, delay time.Duration, driver string) {
@@ -291,7 +310,9 @@ func (h *RegistrationHandler) DeRegisterPlugin(pluginName, endpoint string) {
 		}
 		h.pendingWipes[pluginName] = &cancel
 
+		h.wg.Add(1)
 		go func() {
+			defer h.wg.Done()
 			defer func() {
 				h.mutex.Lock()
 				defer h.mutex.Unlock()

pkg/kubelet/cm/dra/plugin/registration_test.go

@@ -149,15 +149,26 @@ func TestRegistrationHandler(t *testing.T) {
 					// Set expected slice fields for the next call of this reactor.
 					// The reactor will be called next time when resourceslices object is deleted
 					// by the kubelet after plugin deregistration.
-					expectedSliceFields = fields.Set{"spec.nodeName": nodeName, "spec.driver": test.pluginName}
-
+					switch len(expectedSliceFields) {
+					case 1:
+						// Startup cleanup done, now expect cleanup for test plugin.
+						expectedSliceFields = fields.Set{"spec.nodeName": nodeName, "spec.driver": test.pluginName}
+					case 2:
+						// Test plugin cleanup done, now expect cleanup for the other plugin.
+						otherPlugin := pluginA
+						if otherPlugin == test.pluginName {
+							otherPlugin = pluginB
+						}
+						expectedSliceFields = fields.Set{"spec.nodeName": nodeName, "spec.driver": otherPlugin}
+					}
 					return true, nil, err
 				})
 				client = fakeClient
 			}
 
 			// The handler wipes all slices at startup.
-			handler := NewRegistrationHandler(client, getFakeNode, time.Second /* very short wiping delay for testing */)
+			handler := newRegistrationHandler(tCtx, client, getFakeNode, time.Second /* very short wiping delay for testing */)
+			tCtx.Cleanup(handler.Stop)
 			requireNoSlices := func() {
 				t.Helper()
 				if client == nil {