Fix race in setting nominated node

pkg/scheduler/core/generic_scheduler.go

@@ -351,7 +351,7 @@ func (g *genericScheduler) processPreemptionWithExtenders(
 // worth the complexity, especially because we generally expect to have a very
 // small number of nominated pods per node.
 func (g *genericScheduler) getLowerPriorityNominatedPods(pod *v1.Pod, nodeName string) []*v1.Pod {
-	pods := g.schedulingQueue.WaitingPodsForNode(nodeName)
+	pods := g.schedulingQueue.NominatedPodsForNode(nodeName)
 
 	if len(pods) == 0 {
 		return nil
@@ -501,7 +501,7 @@ func addNominatedPods(pod *v1.Pod, meta algorithm.PredicateMetadata,
 		// This may happen only in tests.
 		return false, meta, nodeInfo
 	}
-	nominatedPods := queue.WaitingPodsForNode(nodeInfo.Node().Name)
+	nominatedPods := queue.NominatedPodsForNode(nodeInfo.Node().Name)
 	if nominatedPods == nil || len(nominatedPods) == 0 {
 		return false, meta, nodeInfo
 	}

pkg/scheduler/internal/queue/scheduling_queue.go

@@ -36,6 +36,7 @@ import (
 
 	"k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	ktypes "k8s.io/apimachinery/pkg/types"
 	"k8s.io/client-go/tools/cache"
 	podutil "k8s.io/kubernetes/pkg/api/v1/pod"
 	"k8s.io/kubernetes/pkg/scheduler/algorithm/predicates"
@@ -62,11 +63,14 @@ type SchedulingQueue interface {
 	MoveAllToActiveQueue()
 	AssignedPodAdded(pod *v1.Pod)
 	AssignedPodUpdated(pod *v1.Pod)
-	WaitingPodsForNode(nodeName string) []*v1.Pod
+	NominatedPodsForNode(nodeName string) []*v1.Pod
 	WaitingPods() []*v1.Pod
 	// Close closes the SchedulingQueue so that the goroutine which is
 	// waiting to pop items can exit gracefully.
 	Close()
+	// UpdateNominatedPodForNode adds the given pod to the nominated pod map or
+	// updates it if it already exists.
+	UpdateNominatedPodForNode(pod *v1.Pod, nodeName string)
 	// DeleteNominatedPodIfExists deletes nominatedPod from internal cache
 	DeleteNominatedPodIfExists(pod *v1.Pod)
 	// NumUnschedulablePods returns the number of unschedulable pods exist in the SchedulingQueue.
@@ -150,9 +154,9 @@ func (f *FIFO) AssignedPodUpdated(pod *v1.Pod) {}
 // MoveAllToActiveQueue does nothing in FIFO as all pods are always in the active queue.
 func (f *FIFO) MoveAllToActiveQueue() {}
 
-// WaitingPodsForNode returns pods that are nominated to run on the given node,
+// NominatedPodsForNode returns pods that are nominated to run on the given node,
 // but FIFO does not support it.
-func (f *FIFO) WaitingPodsForNode(nodeName string) []*v1.Pod {
+func (f *FIFO) NominatedPodsForNode(nodeName string) []*v1.Pod {
 	return nil
 }
 
@@ -164,6 +168,9 @@ func (f *FIFO) Close() {
 // DeleteNominatedPodIfExists does nothing in FIFO.
 func (f *FIFO) DeleteNominatedPodIfExists(pod *v1.Pod) {}
 
+// UpdateNominatedPodForNode does nothing in FIFO.
+func (f *FIFO) UpdateNominatedPodForNode(pod *v1.Pod, nodeName string) {}
+
 // NumUnschedulablePods returns the number of unschedulable pods exist in the SchedulingQueue.
 func (f *FIFO) NumUnschedulablePods() int {
 	return 0
@@ -194,10 +201,9 @@ type PriorityQueue struct {
 	activeQ *Heap
 	// unschedulableQ holds pods that have been tried and determined unschedulable.
 	unschedulableQ *UnschedulablePodsMap
-	// nominatedPods is a map keyed by a node name and the value is a list of
-	// pods which are nominated to run on the node. These are pods which can be in
-	// the activeQ or unschedulableQ.
-	nominatedPods map[string][]*v1.Pod
+	// nominatedPods is a structures that stores pods which are nominated to run
+	// on nodes.
+	nominatedPods *nominatedPodMap
 	// receivedMoveRequest is set to true whenever we receive a request to move a
 	// pod from the unschedulableQ to the activeQ, and is set to false, when we pop
 	// a pod from the activeQ. It indicates if we received a move request when a
@@ -239,52 +245,12 @@ func NewPriorityQueue() *PriorityQueue {
 	pq := &PriorityQueue{
 		activeQ:        newHeap(cache.MetaNamespaceKeyFunc, activeQComp),
 		unschedulableQ: newUnschedulablePodsMap(),
-		nominatedPods:  map[string][]*v1.Pod{},
+		nominatedPods:  newNominatedPodMap(),
 	}
 	pq.cond.L = &pq.lock
 	return pq
 }
 
-// addNominatedPodIfNeeded adds a pod to nominatedPods if it has a NominatedNodeName and it does not
-// already exist in the map. Adding an existing pod is not going to update the pod.
-func (p *PriorityQueue) addNominatedPodIfNeeded(pod *v1.Pod) {
-	nnn := NominatedNodeName(pod)
-	if len(nnn) > 0 {
-		for _, np := range p.nominatedPods[nnn] {
-			if np.UID == pod.UID {
-				klog.V(4).Infof("Pod %v/%v already exists in the nominated map!", pod.Namespace, pod.Name)
-				return
-			}
-		}
-		p.nominatedPods[nnn] = append(p.nominatedPods[nnn], pod)
-	}
-}
-
-// deleteNominatedPodIfExists deletes a pod from the nominatedPods.
-// NOTE: this function assumes lock has been acquired in caller.
-func (p *PriorityQueue) deleteNominatedPodIfExists(pod *v1.Pod) {
-	nnn := NominatedNodeName(pod)
-	if len(nnn) > 0 {
-		for i, np := range p.nominatedPods[nnn] {
-			if np.UID == pod.UID {
-				p.nominatedPods[nnn] = append(p.nominatedPods[nnn][:i], p.nominatedPods[nnn][i+1:]...)
-				if len(p.nominatedPods[nnn]) == 0 {
-					delete(p.nominatedPods, nnn)
-				}
-				break
-			}
-		}
-	}
-}
-
-// updateNominatedPod updates a pod in the nominatedPods.
-func (p *PriorityQueue) updateNominatedPod(oldPod, newPod *v1.Pod) {
-	// Even if the nominated node name of the Pod is not changed, we must delete and add it again
-	// to ensure that its pointer is updated.
-	p.deleteNominatedPodIfExists(oldPod)
-	p.addNominatedPodIfNeeded(newPod)
-}
-
 // Add adds a pod to the active queue. It should be called only when a new pod
 // is added so there is no chance the pod is already in either queue.
 func (p *PriorityQueue) Add(pod *v1.Pod) error {
@@ -296,10 +262,9 @@ func (p *PriorityQueue) Add(pod *v1.Pod) error {
 	} else {
 		if p.unschedulableQ.get(pod) != nil {
 			klog.Errorf("Error: pod %v/%v is already in the unschedulable queue.", pod.Namespace, pod.Name)
-			p.deleteNominatedPodIfExists(pod)
 			p.unschedulableQ.delete(pod)
 		}
-		p.addNominatedPodIfNeeded(pod)
+		p.nominatedPods.add(pod, "")
 		p.cond.Broadcast()
 	}
 	return err
@@ -320,7 +285,7 @@ func (p *PriorityQueue) AddIfNotPresent(pod *v1.Pod) error {
 	if err != nil {
 		klog.Errorf("Error adding pod %v/%v to the scheduling queue: %v", pod.Namespace, pod.Name, err)
 	} else {
-		p.addNominatedPodIfNeeded(pod)
+		p.nominatedPods.add(pod, "")
 		p.cond.Broadcast()
 	}
 	return err
@@ -345,12 +310,12 @@ func (p *PriorityQueue) AddUnschedulableIfNotPresent(pod *v1.Pod) error {
 	}
 	if !p.receivedMoveRequest && isPodUnschedulable(pod) {
 		p.unschedulableQ.addOrUpdate(pod)
-		p.addNominatedPodIfNeeded(pod)
+		p.nominatedPods.add(pod, "")
 		return nil
 	}
 	err := p.activeQ.Add(pod)
 	if err == nil {
-		p.addNominatedPodIfNeeded(pod)
+		p.nominatedPods.add(pod, "")
 		p.cond.Broadcast()
 	}
 	return err
@@ -401,13 +366,13 @@ func (p *PriorityQueue) Update(oldPod, newPod *v1.Pod) error {
 	defer p.lock.Unlock()
 	// If the pod is already in the active queue, just update it there.
 	if _, exists, _ := p.activeQ.Get(newPod); exists {
-		p.updateNominatedPod(oldPod, newPod)
+		p.nominatedPods.update(oldPod, newPod)
 		err := p.activeQ.Update(newPod)
 		return err
 	}
 	// If the pod is in the unschedulable queue, updating it may make it schedulable.
 	if usPod := p.unschedulableQ.get(newPod); usPod != nil {
-		p.updateNominatedPod(oldPod, newPod)
+		p.nominatedPods.update(oldPod, newPod)
 		if isPodUpdated(oldPod, newPod) {
 			p.unschedulableQ.delete(usPod)
 			err := p.activeQ.Add(newPod)
@@ -422,7 +387,7 @@ func (p *PriorityQueue) Update(oldPod, newPod *v1.Pod) error {
 	// If pod is not in any of the two queue, we put it in the active queue.
 	err := p.activeQ.Add(newPod)
 	if err == nil {
-		p.addNominatedPodIfNeeded(newPod)
+		p.nominatedPods.add(newPod, "")
 		p.cond.Broadcast()
 	}
 	return err
@@ -433,7 +398,7 @@ func (p *PriorityQueue) Update(oldPod, newPod *v1.Pod) error {
 func (p *PriorityQueue) Delete(pod *v1.Pod) error {
 	p.lock.Lock()
 	defer p.lock.Unlock()
-	p.deleteNominatedPodIfExists(pod)
+	p.nominatedPods.delete(pod)
 	err := p.activeQ.Delete(pod)
 	if err != nil { // The item was probably not found in the activeQ.
 		p.unschedulableQ.delete(pod)
@@ -516,16 +481,13 @@ func (p *PriorityQueue) getUnschedulablePodsWithMatchingAffinityTerm(pod *v1.Pod
 	return podsToMove
 }
 
-// WaitingPodsForNode returns pods that are nominated to run on the given node,
+// NominatedPodsForNode returns pods that are nominated to run on the given node,
 // but they are waiting for other pods to be removed from the node before they
 // can be actually scheduled.
-func (p *PriorityQueue) WaitingPodsForNode(nodeName string) []*v1.Pod {
+func (p *PriorityQueue) NominatedPodsForNode(nodeName string) []*v1.Pod {
 	p.lock.RLock()
 	defer p.lock.RUnlock()
-	if list, ok := p.nominatedPods[nodeName]; ok {
-		return list
-	}
-	return nil
+	return p.nominatedPods.podsForNode(nodeName)
 }
 
 // WaitingPods returns all the waiting pods in the queue.
@@ -551,10 +513,20 @@ func (p *PriorityQueue) Close() {
 	p.cond.Broadcast()
 }
 
-// DeleteNominatedPodIfExists deletes pod from internal cache if it's a nominatedPod
+// DeleteNominatedPodIfExists deletes pod nominatedPods.
 func (p *PriorityQueue) DeleteNominatedPodIfExists(pod *v1.Pod) {
 	p.lock.Lock()
-	p.deleteNominatedPodIfExists(pod)
+	p.nominatedPods.delete(pod)
+	p.lock.Unlock()
+}
+
+// UpdateNominatedPodForNode adds a pod to the nominated pods of the given node.
+// This is called during the preemption process after a node is nominated to run
+// the pod. We update the structure before sending a request to update the pod
+// object to avoid races with the following scheduling cycles.
+func (p *PriorityQueue) UpdateNominatedPodForNode(pod *v1.Pod, nodeName string) {
+	p.lock.Lock()
+	p.nominatedPods.add(pod, nodeName)
 	p.lock.Unlock()
 }
 
@@ -802,3 +774,77 @@ func newHeap(keyFn KeyFunc, lessFn LessFunc) *Heap {
 		},
 	}
 }
+
+// nominatedPodMap is a structure that stores pods nominated to run on nodes.
+// It exists because nominatedNodeName of pod objects stored in the structure
+// may be different than what scheduler has here. We should be able to find pods
+// by their UID and update/delete them.
+type nominatedPodMap struct {
+	// nominatedPods is a map keyed by a node name and the value is a list of
+	// pods which are nominated to run on the node. These are pods which can be in
+	// the activeQ or unschedulableQ.
+	nominatedPods map[string][]*v1.Pod
+	// nominatedPodToNode is map keyed by a Pod UID to the node name where it is
+	// nominated.
+	nominatedPodToNode map[ktypes.UID]string
+}
+
+func (npm *nominatedPodMap) add(p *v1.Pod, nodeName string) {
+	// always delete the pod if it already exist, to ensure we never store more than
+	// one instance of the pod.
+	npm.delete(p)
+
+	nnn := nodeName
+	if len(nnn) == 0 {
+		nnn = NominatedNodeName(p)
+		if len(nnn) == 0 {
+			return
+		}
+	}
+	npm.nominatedPodToNode[p.UID] = nnn
+	for _, np := range npm.nominatedPods[nnn] {
+		if np.UID == p.UID {
+			klog.V(4).Infof("Pod %v/%v already exists in the nominated map!", p.Namespace, p.Name)
+			return
+		}
+	}
+	npm.nominatedPods[nnn] = append(npm.nominatedPods[nnn], p)
+}
+
+func (npm *nominatedPodMap) delete(p *v1.Pod) {
+	nnn, ok := npm.nominatedPodToNode[p.UID]
+	if !ok {
+		return
+	}
+	for i, np := range npm.nominatedPods[nnn] {
+		if np.UID == p.UID {
+			npm.nominatedPods[nnn] = append(npm.nominatedPods[nnn][:i], npm.nominatedPods[nnn][i+1:]...)
+			if len(npm.nominatedPods[nnn]) == 0 {
+				delete(npm.nominatedPods, nnn)
+			}
+			break
+		}
+	}
+	delete(npm.nominatedPodToNode, p.UID)
+}
+
+func (npm *nominatedPodMap) update(oldPod, newPod *v1.Pod) {
+	// We update irrespective of the nominatedNodeName changed or not, to ensure
+	// that pod pointer is updated.
+	npm.delete(oldPod)
+	npm.add(newPod, "")
+}
+
+func (npm *nominatedPodMap) podsForNode(nodeName string) []*v1.Pod {
+	if list, ok := npm.nominatedPods[nodeName]; ok {
+		return list
+	}
+	return nil
+}
+
+func newNominatedPodMap() *nominatedPodMap {
+	return &nominatedPodMap{
+		nominatedPods:      make(map[string][]*v1.Pod),
+		nominatedPodToNode: make(map[ktypes.UID]string),
+	}
+}

pkg/scheduler/internal/queue/scheduling_queue_test.go

@@ -99,8 +99,14 @@ func TestPriorityQueue_Add(t *testing.T) {
 	q.Add(&medPriorityPod)
 	q.Add(&unschedulablePod)
 	q.Add(&highPriorityPod)
-	expectedNominatedPods := map[string][]*v1.Pod{
-		"node1": {&medPriorityPod, &unschedulablePod},
+	expectedNominatedPods := &nominatedPodMap{
+		nominatedPodToNode: map[types.UID]string{
+			medPriorityPod.UID:   "node1",
+			unschedulablePod.UID: "node1",
+		},
+		nominatedPods: map[string][]*v1.Pod{
+			"node1": {&medPriorityPod, &unschedulablePod},
+		},
 	}
 	if !reflect.DeepEqual(q.nominatedPods, expectedNominatedPods) {
 		t.Errorf("Unexpected nominated map after adding pods. Expected: %v, got: %v", expectedNominatedPods, q.nominatedPods)
@@ -114,8 +120,8 @@ func TestPriorityQueue_Add(t *testing.T) {
 	if p, err := q.Pop(); err != nil || p != &unschedulablePod {
 		t.Errorf("Expected: %v after Pop, but got: %v", unschedulablePod.Name, p.Name)
 	}
-	if len(q.nominatedPods["node1"]) != 2 {
-		t.Errorf("Expected medPriorityPod and unschedulablePod to be still present in nomindatePods: %v", q.nominatedPods["node1"])
+	if len(q.nominatedPods.nominatedPods["node1"]) != 2 {
+		t.Errorf("Expected medPriorityPod and unschedulablePod to be still present in nomindatePods: %v", q.nominatedPods.nominatedPods["node1"])
 	}
 }
 
@@ -125,8 +131,14 @@ func TestPriorityQueue_AddIfNotPresent(t *testing.T) {
 	q.AddIfNotPresent(&highPriNominatedPod) // Must not add anything.
 	q.AddIfNotPresent(&medPriorityPod)
 	q.AddIfNotPresent(&unschedulablePod)
-	expectedNominatedPods := map[string][]*v1.Pod{
-		"node1": {&medPriorityPod, &unschedulablePod},
+	expectedNominatedPods := &nominatedPodMap{
+		nominatedPodToNode: map[types.UID]string{
+			medPriorityPod.UID:   "node1",
+			unschedulablePod.UID: "node1",
+		},
+		nominatedPods: map[string][]*v1.Pod{
+			"node1": {&medPriorityPod, &unschedulablePod},
+		},
 	}
 	if !reflect.DeepEqual(q.nominatedPods, expectedNominatedPods) {
 		t.Errorf("Unexpected nominated map after adding pods. Expected: %v, got: %v", expectedNominatedPods, q.nominatedPods)
@@ -137,8 +149,8 @@ func TestPriorityQueue_AddIfNotPresent(t *testing.T) {
 	if p, err := q.Pop(); err != nil || p != &unschedulablePod {
 		t.Errorf("Expected: %v after Pop, but got: %v", unschedulablePod.Name, p.Name)
 	}
-	if len(q.nominatedPods["node1"]) != 2 {
-		t.Errorf("Expected medPriorityPod and unschedulablePod to be still present in nomindatePods: %v", q.nominatedPods["node1"])
+	if len(q.nominatedPods.nominatedPods["node1"]) != 2 {
+		t.Errorf("Expected medPriorityPod and unschedulablePod to be still present in nomindatePods: %v", q.nominatedPods.nominatedPods["node1"])
 	}
 	if q.unschedulableQ.get(&highPriNominatedPod) != &highPriNominatedPod {
 		t.Errorf("Pod %v was not found in the unschedulableQ.", highPriNominatedPod.Name)
@@ -151,8 +163,15 @@ func TestPriorityQueue_AddUnschedulableIfNotPresent(t *testing.T) {
 	q.AddUnschedulableIfNotPresent(&highPriNominatedPod) // Must not add anything.
 	q.AddUnschedulableIfNotPresent(&medPriorityPod)      // This should go to activeQ.
 	q.AddUnschedulableIfNotPresent(&unschedulablePod)
-	expectedNominatedPods := map[string][]*v1.Pod{
-		"node1": {&highPriNominatedPod, &medPriorityPod, &unschedulablePod},
+	expectedNominatedPods := &nominatedPodMap{
+		nominatedPodToNode: map[types.UID]string{
+			medPriorityPod.UID:      "node1",
+			unschedulablePod.UID:    "node1",
+			highPriNominatedPod.UID: "node1",
+		},
+		nominatedPods: map[string][]*v1.Pod{
+			"node1": {&highPriNominatedPod, &medPriorityPod, &unschedulablePod},
+		},
 	}
 	if !reflect.DeepEqual(q.nominatedPods, expectedNominatedPods) {
 		t.Errorf("Unexpected nominated map after adding pods. Expected: %v, got: %v", expectedNominatedPods, q.nominatedPods)
@@ -163,7 +182,7 @@ func TestPriorityQueue_AddUnschedulableIfNotPresent(t *testing.T) {
 	if p, err := q.Pop(); err != nil || p != &medPriorityPod {
 		t.Errorf("Expected: %v after Pop, but got: %v", medPriorityPod.Name, p.Name)
 	}
-	if len(q.nominatedPods) != 1 {
+	if len(q.nominatedPods.nominatedPods) != 1 {
 		t.Errorf("Expected nomindatePods to have one element: %v", q.nominatedPods)
 	}
 	if q.unschedulableQ.get(&unschedulablePod) != &unschedulablePod {
@@ -180,8 +199,8 @@ func TestPriorityQueue_Pop(t *testing.T) {
 		if p, err := q.Pop(); err != nil || p != &medPriorityPod {
 			t.Errorf("Expected: %v after Pop, but got: %v", medPriorityPod.Name, p.Name)
 		}
-		if len(q.nominatedPods["node1"]) != 1 {
-			t.Errorf("Expected medPriorityPod to be present in nomindatePods: %v", q.nominatedPods["node1"])
+		if len(q.nominatedPods.nominatedPods["node1"]) != 1 {
+			t.Errorf("Expected medPriorityPod to be present in nomindatePods: %v", q.nominatedPods.nominatedPods["node1"])
 		}
 	}()
 	q.Add(&medPriorityPod)
@@ -194,7 +213,7 @@ func TestPriorityQueue_Update(t *testing.T) {
 	if _, exists, _ := q.activeQ.Get(&highPriorityPod); !exists {
 		t.Errorf("Expected %v to be added to activeQ.", highPriorityPod.Name)
 	}
-	if len(q.nominatedPods) != 0 {
+	if len(q.nominatedPods.nominatedPods) != 0 {
 		t.Errorf("Expected nomindatePods to be empty: %v", q.nominatedPods)
 	}
 	// Update highPriorityPod and add a nominatedNodeName to it.
@@ -202,7 +221,7 @@ func TestPriorityQueue_Update(t *testing.T) {
 	if q.activeQ.data.Len() != 1 {
 		t.Error("Expected only one item in activeQ.")
 	}
-	if len(q.nominatedPods) != 1 {
+	if len(q.nominatedPods.nominatedPods) != 1 {
 		t.Errorf("Expected one item in nomindatePods map: %v", q.nominatedPods)
 	}
 	// Updating an unschedulable pod which is not in any of the two queues, should
@@ -235,11 +254,13 @@ func TestPriorityQueue_Delete(t *testing.T) {
 	if _, exists, _ := q.activeQ.Get(&highPriNominatedPod); exists {
 		t.Errorf("Didn't expect %v to be in activeQ.", highPriorityPod.Name)
 	}
-	if len(q.nominatedPods) != 1 {
-		t.Errorf("Expected nomindatePods to have only 'unschedulablePod': %v", q.nominatedPods)
+	if len(q.nominatedPods.nominatedPods) != 1 {
+		t.Errorf("Expected nomindatePods to have only 'unschedulablePod': %v", q.nominatedPods.nominatedPods)
+	}
+	if err := q.Delete(&unschedulablePod); err != nil {
+		t.Errorf("delete failed: %v", err)
 	}
-	q.Delete(&unschedulablePod)
-	if len(q.nominatedPods) != 0 {
+	if len(q.nominatedPods.nominatedPods) != 0 {
 		t.Errorf("Expected nomindatePods to be empty: %v", q.nominatedPods)
 	}
 }
@@ -311,7 +332,7 @@ func TestPriorityQueue_AssignedPodAdded(t *testing.T) {
 	}
 }
 
-func TestPriorityQueue_WaitingPodsForNode(t *testing.T) {
+func TestPriorityQueue_NominatedPodsForNode(t *testing.T) {
 	q := NewPriorityQueue()
 	q.Add(&medPriorityPod)
 	q.Add(&unschedulablePod)
@@ -320,14 +341,83 @@ func TestPriorityQueue_WaitingPodsForNode(t *testing.T) {
 		t.Errorf("Expected: %v after Pop, but got: %v", highPriorityPod.Name, p.Name)
 	}
 	expectedList := []*v1.Pod{&medPriorityPod, &unschedulablePod}
-	if !reflect.DeepEqual(expectedList, q.WaitingPodsForNode("node1")) {
+	if !reflect.DeepEqual(expectedList, q.NominatedPodsForNode("node1")) {
 		t.Error("Unexpected list of nominated Pods for node.")
 	}
-	if q.WaitingPodsForNode("node2") != nil {
+	if q.NominatedPodsForNode("node2") != nil {
 		t.Error("Expected list of nominated Pods for node2 to be empty.")
 	}
 }
 
+func TestPriorityQueue_UpdateNominatedPodForNode(t *testing.T) {
+	q := NewPriorityQueue()
+	if err := q.Add(&medPriorityPod); err != nil {
+		t.Errorf("add failed: %v", err)
+	}
+	// Update unschedulablePod on a different node than specified in the pod.
+	q.UpdateNominatedPodForNode(&unschedulablePod, "node5")
+
+	// Update nominated node name of a pod on a node that is not specified in the pod object.
+	q.UpdateNominatedPodForNode(&highPriorityPod, "node2")
+	expectedNominatedPods := &nominatedPodMap{
+		nominatedPodToNode: map[types.UID]string{
+			medPriorityPod.UID:   "node1",
+			highPriorityPod.UID:  "node2",
+			unschedulablePod.UID: "node5",
+		},
+		nominatedPods: map[string][]*v1.Pod{
+			"node1": {&medPriorityPod},
+			"node2": {&highPriorityPod},
+			"node5": {&unschedulablePod},
+		},
+	}
+	if !reflect.DeepEqual(q.nominatedPods, expectedNominatedPods) {
+		t.Errorf("Unexpected nominated map after adding pods. Expected: %v, got: %v", expectedNominatedPods, q.nominatedPods)
+	}
+	if p, err := q.Pop(); err != nil || p != &medPriorityPod {
+		t.Errorf("Expected: %v after Pop, but got: %v", medPriorityPod.Name, p.Name)
+	}
+	// List of nominated pods shouldn't change after popping them from the queue.
+	if !reflect.DeepEqual(q.nominatedPods, expectedNominatedPods) {
+		t.Errorf("Unexpected nominated map after popping pods. Expected: %v, got: %v", expectedNominatedPods, q.nominatedPods)
+	}
+	// Update one of the nominated pods that doesn't have nominatedNodeName in the
+	// pod object. It should be updated correctly.
+	q.UpdateNominatedPodForNode(&highPriorityPod, "node4")
+	expectedNominatedPods = &nominatedPodMap{
+		nominatedPodToNode: map[types.UID]string{
+			medPriorityPod.UID:   "node1",
+			highPriorityPod.UID:  "node4",
+			unschedulablePod.UID: "node5",
+		},
+		nominatedPods: map[string][]*v1.Pod{
+			"node1": {&medPriorityPod},
+			"node4": {&highPriorityPod},
+			"node5": {&unschedulablePod},
+		},
+	}
+	if !reflect.DeepEqual(q.nominatedPods, expectedNominatedPods) {
+		t.Errorf("Unexpected nominated map after updating pods. Expected: %v, got: %v", expectedNominatedPods, q.nominatedPods)
+	}
+
+	// Delete a nominated pod that doesn't have nominatedNodeName in the pod
+	// object. It should be deleted.
+	q.DeleteNominatedPodIfExists(&highPriorityPod)
+	expectedNominatedPods = &nominatedPodMap{
+		nominatedPodToNode: map[types.UID]string{
+			medPriorityPod.UID:   "node1",
+			unschedulablePod.UID: "node5",
+		},
+		nominatedPods: map[string][]*v1.Pod{
+			"node1": {&medPriorityPod},
+			"node5": {&unschedulablePod},
+		},
+	}
+	if !reflect.DeepEqual(q.nominatedPods, expectedNominatedPods) {
+		t.Errorf("Unexpected nominated map after deleting pods. Expected: %v, got: %v", expectedNominatedPods, q.nominatedPods)
+	}
+}
+
 func TestUnschedulablePodsMap(t *testing.T) {
 	var pods = []*v1.Pod{
 		{

pkg/scheduler/scheduler.go

@@ -328,11 +328,19 @@ func (sched *Scheduler) preempt(preemptor *v1.Pod, scheduleErr error) (string, e
 	var nodeName = ""
 	if node != nil {
 		nodeName = node.Name
+		// Update the scheduling queue with the nominated pod information. Without
+		// this, there would be a race condition between the next scheduling cycle
+		// and the time the scheduler receives a Pod Update for the nominated pod.
+		sched.config.SchedulingQueue.UpdateNominatedPodForNode(preemptor, nodeName)
+
+		// Make a call to update nominated node name of the pod on the API server.
 		err = sched.config.PodPreemptor.SetNominatedNodeName(preemptor, nodeName)
 		if err != nil {
 			klog.Errorf("Error in preemption process. Cannot update pod %v/%v annotations: %v", preemptor.Namespace, preemptor.Name, err)
+			sched.config.SchedulingQueue.DeleteNominatedPodIfExists(preemptor)
 			return "", err
 		}
+
 		for _, victim := range victims {
 			if err := sched.config.PodPreemptor.DeletePod(victim); err != nil {
 				klog.Errorf("Error preempting pod %v/%v: %v", victim.Namespace, victim.Name, err)