Fix race condition in config-manager when label is unset

When the node label (nvidia.com/device-plugin.config) is not set, a race
condition could cause the config-manager to hang indefinitely on startup.

The issue occurred when the informer's AddFunc fired before the first Get()
call, setting current="" and broadcasting. When Get() was subsequently called,
it found lastRead == current (both empty strings) and waited forever, as no
future events would wake it up.

This fix adds an 'initialized' flag to SyncableConfig to ensure the first
Get() call never waits, regardless of timing. Subsequent Get() calls still
wait properly when the value hasn't changed.

Author: uristernik

cmd/config-manager/main.go

@@ -79,10 +79,11 @@ type Flags struct {
 // Multiple calls to Set() do not queue, meaning that only calls to Get() made
 // *before* a call to Set() will be notified.
 type SyncableConfig struct {
-	cond     *sync.Cond
-	mutex    sync.Mutex
-	current  string
-	lastRead string
+	cond        *sync.Cond
+	mutex       sync.Mutex
+	current     string
+	lastRead    string
+	initialized bool
 }
 
 // NewSyncableConfig creates a new SyncableConfig
@@ -106,9 +107,10 @@ func (m *SyncableConfig) Set(value string) {
 func (m *SyncableConfig) Get() string {
 	m.mutex.Lock()
 	defer m.mutex.Unlock()
-	if m.lastRead == m.current {
+	if m.initialized && m.lastRead == m.current {
 		m.cond.Wait()
 	}
+	m.initialized = true
 	m.lastRead = m.current
 	return m.lastRead
 }