fix kubelet syncLoop busy loop upon close of updates chan

pkg/kubelet/kubelet.go

@@ -1896,17 +1896,19 @@ func (kl *Kubelet) syncLoop(updates <-chan PodUpdate, handler SyncHandler) {
 			}
 			housekeepingTimestamp = time.Now()
 		}
-		kl.syncLoopIteration(updates, handler)
+		if !kl.syncLoopIteration(updates, handler) {
+			break
+		}
 	}
 }
 
-func (kl *Kubelet) syncLoopIteration(updates <-chan PodUpdate, handler SyncHandler) {
+func (kl *Kubelet) syncLoopIteration(updates <-chan PodUpdate, handler SyncHandler) bool {
 	kl.syncLoopMonitor.Store(time.Now())
 	select {
-	case u, ok := <-updates:
-		if !ok {
+	case u, open := <-updates:
+		if !open {
 			glog.Errorf("Update channel is closed. Exiting the sync loop.")
-			return
+			return false
 		}
 		switch u.Op {
 		case ADD:
@@ -1928,6 +1930,7 @@ func (kl *Kubelet) syncLoopIteration(updates <-chan PodUpdate, handler SyncHandl
 		handler.HandlePodSyncs(kl.podManager.GetPods())
 	}
 	kl.syncLoopMonitor.Store(time.Now())
+	return true
 }
 
 func (kl *Kubelet) dispatchWork(pod *api.Pod, syncType SyncPodType, mirrorPod *api.Pod, start time.Time) {

pkg/kubelet/kubelet_test.go

@@ -329,6 +329,26 @@ func TestSyncLoopTimeUpdate(t *testing.T) {
 	}
 }
 
+func TestSyncLoopAbort(t *testing.T) {
+	testKubelet := newTestKubelet(t)
+	testKubelet.fakeCadvisor.On("MachineInfo").Return(&cadvisorApi.MachineInfo{}, nil)
+	kubelet := testKubelet.kubelet
+	kubelet.lastTimestampRuntimeUp = time.Now()
+	kubelet.networkConfigured = true
+
+	ch := make(chan PodUpdate)
+	close(ch)
+
+	// sanity check (also prevent this test from hanging in the next step)
+	ok := kubelet.syncLoopIteration(ch, kubelet)
+	if ok {
+		t.Fatalf("expected syncLoopIteration to return !ok since update chan was closed")
+	}
+
+	// this should terminate immediately; if it hangs then the syncLoopIteration isn't aborting properly
+	kubelet.syncLoop(ch, kubelet)
+}
+
 func TestSyncPodsStartPod(t *testing.T) {
 	testKubelet := newTestKubelet(t)
 	testKubelet.fakeCadvisor.On("MachineInfo").Return(&cadvisorApi.MachineInfo{}, nil)