Fix race in informer transformers

staging/src/k8s.io/client-go/tools/cache/controller_test.go

@@ -20,6 +20,7 @@ import (
 	"fmt"
 	"math/rand"
 	"sync"
+	"sync/atomic"
 	"testing"
 	"time"
 
@@ -575,6 +576,114 @@ func TestTransformingInformer(t *testing.T) {
 	close(stopCh)
 }
 
+func TestTransformingInformerRace(t *testing.T) {
+	// source simulates an apiserver object endpoint.
+	source := fcache.NewFakeControllerSource()
+
+	label := "to-be-transformed"
+	makePod := func(name string) *v1.Pod {
+		return &v1.Pod{
+			ObjectMeta: metav1.ObjectMeta{
+				Name:      name,
+				Namespace: "namespace",
+				Labels:    map[string]string{label: "true"},
+			},
+			Spec: v1.PodSpec{
+				Hostname: "hostname",
+			},
+		}
+	}
+
+	badTransform := atomic.Bool{}
+	podTransformer := func(obj interface{}) (interface{}, error) {
+		pod, ok := obj.(*v1.Pod)
+		if !ok {
+			return nil, fmt.Errorf("unexpected object type: %T", obj)
+		}
+		if pod.ObjectMeta.Labels[label] != "true" {
+			badTransform.Store(true)
+			return nil, fmt.Errorf("object already transformed: %#v", obj)
+		}
+		pod.ObjectMeta.Labels[label] = "false"
+		return pod, nil
+	}
+
+	numObjs := 5
+	for i := 0; i < numObjs; i++ {
+		source.Add(makePod(fmt.Sprintf("pod-%d", i)))
+	}
+
+	type event struct{}
+	events := make(chan event, numObjs)
+	recordEvent := func(eventType watch.EventType, previous, current interface{}) {
+		events <- event{}
+	}
+	checkEvents := func(count int) {
+		for i := 0; i < count; i++ {
+			<-events
+		}
+	}
+	store, controller := NewTransformingInformer(
+		source,
+		&v1.Pod{},
+		5*time.Millisecond,
+		ResourceEventHandlerDetailedFuncs{
+			AddFunc:    func(obj interface{}, isInInitialList bool) { recordEvent(watch.Added, nil, obj) },
+			UpdateFunc: func(oldObj, newObj interface{}) { recordEvent(watch.Modified, oldObj, newObj) },
+			DeleteFunc: func(obj interface{}) { recordEvent(watch.Deleted, obj, nil) },
+		},
+		podTransformer,
+	)
+
+	stopCh := make(chan struct{})
+	go controller.Run(stopCh)
+
+	checkEvents(numObjs)
+
+	// Periodically fetch objects to ensure no access races.
+	wg := sync.WaitGroup{}
+	errors := make(chan error, numObjs)
+	for i := 0; i < numObjs; i++ {
+		wg.Add(1)
+		go func(index int) {
+			defer wg.Done()
+			key := fmt.Sprintf("namespace/pod-%d", index)
+			for {
+				select {
+				case <-stopCh:
+					return
+				default:
+				}
+
+				obj, ok, err := store.GetByKey(key)
+				if !ok || err != nil {
+					errors <- fmt.Errorf("couldn't get the object for %v", key)
+					return
+				}
+				pod := obj.(*v1.Pod)
+				if pod.ObjectMeta.Labels[label] != "false" {
+					errors <- fmt.Errorf("unexpected object: %#v", pod)
+					return
+				}
+			}
+		}(i)
+	}
+
+	// Let resyncs to happen for some time.
+	time.Sleep(time.Second)
+
+	close(stopCh)
+	wg.Wait()
+	close(errors)
+	for err := range errors {
+		t.Error(err)
+	}
+
+	if badTransform.Load() {
+		t.Errorf("unexpected transformation happened")
+	}
+}
+
 func TestDeletionHandlingObjectToName(t *testing.T) {
 	cm := &v1.ConfigMap{
 		ObjectMeta: metav1.ObjectMeta{

staging/src/k8s.io/client-go/tools/cache/delta_fifo.go

@@ -139,20 +139,17 @@ type DeltaFIFO struct {
 }
 
 // TransformFunc allows for transforming an object before it will be processed.
-// TransformFunc (similarly to ResourceEventHandler functions) should be able
-// to correctly handle the tombstone of type cache.DeletedFinalStateUnknown.
-//
-// New in v1.27: In such cases, the contained object will already have gone
-// through the transform object separately (when it was added / updated prior
-// to the delete), so the TransformFunc can likely safely ignore such objects
-// (i.e., just return the input object).
 //
 // The most common usage pattern is to clean-up some parts of the object to
 // reduce component memory usage if a given component doesn't care about them.
 //
-// New in v1.27: unless the object is a DeletedFinalStateUnknown, TransformFunc
-// sees the object before any other actor, and it is now safe to mutate the
-// object in place instead of making a copy.
+// New in v1.27: TransformFunc sees the object before any other actor, and it
+// is now safe to mutate the object in place instead of making a copy.
+//
+// It's recommended for the TransformFunc to be idempotent.
+// It MUST be idempotent if objects already present in the cache are passed to
+// the Replace() to avoid re-mutating them. Default informers do not pass
+// existing objects to Replace though.
 //
 // Note that TransformFunc is called while inserting objects into the
 // notification queue and is therefore extremely performance sensitive; please
@@ -440,22 +437,38 @@ func isDeletionDup(a, b *Delta) *Delta {
 // queueActionLocked appends to the delta list for the object.
 // Caller must lock first.
 func (f *DeltaFIFO) queueActionLocked(actionType DeltaType, obj interface{}) error {
+	return f.queueActionInternalLocked(actionType, actionType, obj)
+}
+
+// queueActionInternalLocked appends to the delta list for the object.
+// The actionType is emitted and must honor emitDeltaTypeReplaced.
+// The internalActionType is only used within this function and must
+// ignore emitDeltaTypeReplaced.
+// Caller must lock first.
+func (f *DeltaFIFO) queueActionInternalLocked(actionType, internalActionType DeltaType, obj interface{}) error {
 	id, err := f.KeyOf(obj)
 	if err != nil {
 		return KeyError{obj, err}
 	}
 
 	// Every object comes through this code path once, so this is a good
-	// place to call the transform func.  If obj is a
-	// DeletedFinalStateUnknown tombstone, then the containted inner object
-	// will already have gone through the transformer, but we document that
-	// this can happen. In cases involving Replace(), such an object can
-	// come through multiple times.
+	// place to call the transform func.
+	//
+	// If obj is a DeletedFinalStateUnknown tombstone or the action is a Sync,
+	// then the object have already gone through the transformer.
+	//
+	// If the objects already present in the cache are passed to Replace(),
+	// the transformer must be idempotent to avoid re-mutating them,
+	// or coordinate with all readers from the cache to avoid data races.
+	// Default informers do not pass existing objects to Replace.
 	if f.transformer != nil {
-		var err error
-		obj, err = f.transformer(obj)
-		if err != nil {
-			return err
+		_, isTombstone := obj.(DeletedFinalStateUnknown)
+		if !isTombstone && internalActionType != Sync {
+			var err error
+			obj, err = f.transformer(obj)
+			if err != nil {
+				return err
+			}
 		}
 	}
 
@@ -638,7 +651,7 @@ func (f *DeltaFIFO) Replace(list []interface{}, _ string) error {
 			return KeyError{item, err}
 		}
 		keys.Insert(key)
-		if err := f.queueActionLocked(action, item); err != nil {
+		if err := f.queueActionInternalLocked(action, Replaced, item); err != nil {
 			return fmt.Errorf("couldn't enqueue object: %v", err)
 		}
 	}