Process plugins found before the ones watched

Currently, the method `pluginwatcher.traversePluginDir` descends into
a directory adding filesystem watchers and creating synthetic `create`
events when it finds sockets files. However, a race condition might
happen when a recently-added watcher observes a `delete` event in a
socket file before `pluginwatcher.traversePlugindir` itself notices
this file.

This patch changes this behavior by registering watchers on
directories, enqueueing and processing `create` events from sockets
found, and only then processing the events from the registered watchers.

pkg/kubelet/util/pluginwatcher/BUILD

@@ -29,6 +29,7 @@ go_test(
     embed = [":go_default_library"],
     deps = [
         "//pkg/kubelet/apis/pluginregistration/v1:go_default_library",
+        "//staging/src/k8s.io/apimachinery/pkg/util/wait:go_default_library",
         "//vendor/github.com/stretchr/testify/require:go_default_library",
         "//vendor/k8s.io/klog:go_default_library",
     ],

pkg/kubelet/util/pluginwatcher/plugin_watcher.go

@@ -102,9 +102,24 @@ func (w *Watcher) Start() error {
 	}
 	w.fsWatcher = fsWatcher
 
+	// Traverse plugin dir and add filesystem watchers before starting the plugin processing goroutine.
+	if err := w.traversePluginDir(w.path); err != nil {
+		w.Stop()
+		return fmt.Errorf("failed to traverse plugin socket path %q, err: %v", w.path, err)
+	}
+
+	// Traverse deprecated plugin dir, if specified.
+	if len(w.deprecatedPath) != 0 {
+		if err := w.traversePluginDir(w.deprecatedPath); err != nil {
+			w.Stop()
+			return fmt.Errorf("failed to traverse deprecated plugin socket path %q, err: %v", w.deprecatedPath, err)
+		}
+	}
+
 	w.wg.Add(1)
 	go func(fsWatcher *fsnotify.Watcher) {
 		defer w.wg.Done()
+
 		for {
 			select {
 			case event := <-fsWatcher.Events:
@@ -139,20 +154,6 @@ func (w *Watcher) Start() error {
 		}
 	}(fsWatcher)
 
-	// Traverse plugin dir after starting the plugin processing goroutine
-	if err := w.traversePluginDir(w.path); err != nil {
-		w.Stop()
-		return fmt.Errorf("failed to traverse plugin socket path %q, err: %v", w.path, err)
-	}
-
-	// Traverse deprecated plugin dir, if specified.
-	if len(w.deprecatedPath) != 0 {
-		if err := w.traversePluginDir(w.deprecatedPath); err != nil {
-			w.Stop()
-			return fmt.Errorf("failed to traverse deprecated plugin socket path %q, err: %v", w.deprecatedPath, err)
-		}
-	}
-
 	return nil
 }
 
@@ -211,14 +212,14 @@ func (w *Watcher) traversePluginDir(dir string) error {
 				return fmt.Errorf("failed to watch %s, err: %v", path, err)
 			}
 		case mode&os.ModeSocket != 0:
-			w.wg.Add(1)
-			go func() {
-				defer w.wg.Done()
-				w.fsWatcher.Events <- fsnotify.Event{
-					Name: path,
-					Op:   fsnotify.Create,
-				}
-			}()
+			event := fsnotify.Event{
+				Name: path,
+				Op:   fsnotify.Create,
+			}
+			//TODO: Handle errors by taking corrective measures
+			if err := w.handleCreateEvent(event); err != nil {
+				klog.Errorf("error %v when handling create event: %s", err, event)
+			}
 		default:
 			klog.V(5).Infof("Ignoring file %s with mode %v", path, mode)
 		}

pkg/kubelet/util/pluginwatcher/plugin_watcher_test.go

@@ -27,6 +27,7 @@ import (
 
 	"github.com/stretchr/testify/require"
 
+	"k8s.io/apimachinery/pkg/util/wait"
 	"k8s.io/klog"
 	registerapi "k8s.io/kubernetes/pkg/kubelet/apis/pluginregistration/v1"
 )
@@ -173,9 +174,6 @@ func TestPluginRegistrationAtKubeletStart(t *testing.T) {
 		plugins[i] = p
 	}
 
-	w := newWatcherWithHandler(t, hdlr, false /* testDeprecatedDir */)
-	defer func() { require.NoError(t, w.Stop()) }()
-
 	var wg sync.WaitGroup
 	for i := 0; i < len(plugins); i++ {
 		wg.Add(1)
@@ -189,6 +187,9 @@ func TestPluginRegistrationAtKubeletStart(t *testing.T) {
 		}(plugins[i])
 	}
 
+	w := newWatcherWithHandler(t, hdlr, false /* testDeprecatedDir */)
+	defer func() { require.NoError(t, w.Stop()) }()
+
 	c := make(chan struct{})
 	go func() {
 		defer close(c)
@@ -198,7 +199,7 @@ func TestPluginRegistrationAtKubeletStart(t *testing.T) {
 	select {
 	case <-c:
 		return
-	case <-time.After(2 * time.Second):
+	case <-time.After(wait.ForeverTestTimeout):
 		t.Fatalf("Timeout while waiting for the plugin registration status")
 	}
 }
@@ -238,11 +239,22 @@ func TestPlugiRegistrationFailureWithUnsupportedVersionAtKubeletStart(t *testing
 	hdlr := NewExampleHandler(supportedVersions, false /* permitDeprecatedDir */)
 	hdlr.AddPluginName(pluginName)
 
+	c := make(chan struct{})
+	go func() {
+		defer close(c)
+		require.True(t, waitForEvent(t, exampleEventValidate, hdlr.EventChan(p.pluginName)))
+		require.False(t, waitForPluginRegistrationStatus(t, p.registrationStatus))
+	}()
+
 	w := newWatcherWithHandler(t, hdlr, false /* testDeprecatedDir */)
 	defer func() { require.NoError(t, w.Stop()) }()
 
-	require.True(t, waitForEvent(t, exampleEventValidate, hdlr.EventChan(p.pluginName)))
-	require.False(t, waitForPluginRegistrationStatus(t, p.registrationStatus))
+	select {
+	case <-c:
+		return
+	case <-time.After(wait.ForeverTestTimeout):
+		t.Fatalf("Timeout while waiting for the plugin registration status")
+	}
 }
 
 func waitForPluginRegistrationStatus(t *testing.T, statusChan chan registerapi.RegistrationStatus) bool {
@@ -259,7 +271,7 @@ func waitForEvent(t *testing.T, expected examplePluginEvent, eventChan chan exam
 	select {
 	case event := <-eventChan:
 		return event == expected
-	case <-time.After(2 * time.Second):
+	case <-time.After(wait.ForeverTestTimeout):
 		t.Fatalf("Timed out while waiting for registration status %v", expected)
 	}