pkg/manager: prevent deadlock on ReproLoop cancellation

When the context is cancelled, no one may be polling the pingQueue, yet
we write to it synchronously.

Wrap it in a select{} statement and add a test to ensure that the loop
reacts properly to the context cancellation.

Author: a-nogikh

pkg/manager/repro.go

@@ -230,7 +230,11 @@ func (r *ReproLoop) Loop(ctx context.Context) {
 			r.mu.Unlock()
 
 			r.parallel <- struct{}{}
-			r.pingQueue <- struct{}{}
+			// If the context is cancelled, no one is listening on pingQueue.
+			select {
+			case r.pingQueue <- struct{}{}:
+			default:
+			}
 		}()
 	}
 }

pkg/manager/repro_test.go

@@ -123,6 +123,28 @@ func TestReproRWRace(t *testing.T) {
 	mock.onVMShutdown(t, obj)
 }
 
+func TestCancelRunningRepro(t *testing.T) {
+	mock := &reproMgrMock{
+		run: make(chan runCallback),
+	}
+	obj := NewReproLoop(mock, 1, false)
+	ctx, done := context.WithCancel(context.Background())
+	complete := make(chan struct{})
+	go func() {
+		obj.Loop(ctx)
+		close(complete)
+	}()
+
+	defer func() {
+		<-complete
+	}()
+
+	obj.Enqueue(&Crash{Report: &report.Report{Title: "A"}})
+	obj.Enqueue(&Crash{Report: &report.Report{Title: "B"}})
+	<-mock.run
+	done()
+}
+
 type reproMgrMock struct {
 	reserved       atomic.Int64
 	run            chan runCallback