libcontainerd: use cancellable context for events

The event subscriber can only be cancelled by cancelling the context.
In the case where we have to restart event processing we are never
cancelling the old subscribiption.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

libcontainerd/remote/client.go

@@ -722,9 +722,12 @@ func (c *client) waitServe(ctx context.Context) bool {
 	// `IsServing` will actually block until the service is ready.
 	// However it can return early, so we'll loop with a delay to handle it.
 	for {
-		serving, _ := c.client.IsServing(ctx)
-		if ctx.Err() != nil {
-			return false
+		serving, err := c.client.IsServing(ctx)
+		if err != nil {
+			if errors.Is(err, context.DeadlineExceeded) || errors.Is(err, context.Canceled) {
+				return false
+			}
+			logrus.WithError(err).Warn("Error while testing if containerd API is ready")
 		}
 
 		if serving {
@@ -748,9 +751,16 @@ func (c *client) processEventStream(ctx context.Context, ns string) {
 		ei  libcontainerdtypes.EventInfo
 	)
 
+	// Create a new context specifically for this subscription.
+	// The context must be cancelled to cancel the subscription.
+	// In cases where we have to restart event stream processing,
+	//   we'll need the original context b/c this one will be cancelled
+	subCtx, cancel := context.WithCancel(ctx)
+	defer cancel()
+
 	// Filter on both namespace *and* topic. To create an "and" filter,
 	// this must be a single, comma-separated string
-	eventStream, errC := c.client.EventService().Subscribe(ctx, "namespace=="+ns+",topic~=|^/tasks/|")
+	eventStream, errC := c.client.EventService().Subscribe(subCtx, "namespace=="+ns+",topic~=|^/tasks/|")
 
 	c.logger.Debug("processing event stream")