fix(prefix-cache): race conditions in indexer lock management (kubernetes-sigs#2501)

Signed-off-by: Sam Batschelet <sbatschelet@gmail.com>

Author: hexfusion

pkg/epp/framework/plugins/scheduling/scorer/prefix/indexer.go

@@ -52,6 +52,8 @@ func newIndexer(ctx context.Context, defaultLRUSize int) *indexer {
 // Add adds a list of prefix hashes to the cache, tied to the server.
 func (i *indexer) Add(hashes []BlockHash, pod Server) {
 	i.mu.Lock()
+	defer i.mu.Unlock()
+
 	// Check if the LRU pod exist
 	lruForPod, exists := i.podToLRU[pod.ServerID]
 	if !exists {
@@ -64,15 +66,12 @@ func (i *indexer) Add(hashes []BlockHash, pod Server) {
 		lruForPod = newLRU
 	}
 
-	i.mu.Unlock()
-
 	// Add to LRU (may evict)
 	for _, hash := range hashes {
 		lruForPod.Add(hash, struct{}{})
 	}
 
-	// Update hashToPods once under lock
-	i.mu.Lock()
+	// Update hashToPods
 	for _, hash := range hashes {
 		podIDs := i.hashToPods[hash]
 		if podIDs == nil {
@@ -81,8 +80,6 @@ func (i *indexer) Add(hashes []BlockHash, pod Server) {
 		podIDs[pod.ServerID] = struct{}{}
 		i.hashToPods[hash] = podIDs
 	}
-
-	i.mu.Unlock()
 }
 
 // Get returns a set of servers that have the given prefix hash cached.
@@ -103,8 +100,6 @@ func (i *indexer) Get(hash BlockHash) podSet {
 // makeEvictionFn returns a per-pod LRU eviction callback that removes the pod from hashToPods on eviction.
 func (i *indexer) makeEvictionFn(pod ServerID) func(BlockHash, struct{}) {
 	return func(hash BlockHash, _ struct{}) {
-		i.mu.Lock()
-		defer i.mu.Unlock()
 		// Remove the pod from the hash→pods map
 		if podSet, ok := i.hashToPods[hash]; ok {
 			delete(podSet, pod)
@@ -156,10 +151,10 @@ func (i *indexer) reportLRUSize(ctx context.Context, interval time.Duration) {
 
 // RemovePod removes a pod and its associated entries from the indexer.
 func (i *indexer) RemovePod(pod ServerID) {
-	i.mu.RLock()
-	lruCache, exists := i.podToLRU[pod]
-	i.mu.RUnlock()
+	i.mu.Lock()
+	defer i.mu.Unlock()
 
+	lruCache, exists := i.podToLRU[pod]
 	if !exists {
 		return
 	}
@@ -169,9 +164,7 @@ func (i *indexer) RemovePod(pod ServerID) {
 		lruCache.Remove(hash)
 	}
 
-	i.mu.Lock()
 	delete(i.podToLRU, pod)
-	i.mu.Unlock()
 }
 
 // Pods returns the list of all pods currently tracked in the indexer.

pkg/epp/framework/plugins/scheduling/scorer/prefix/indexer_test.go

@@ -18,6 +18,7 @@ package prefix
 
 import (
 	"context"
+	"sync"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -110,3 +111,23 @@ func TestIndexer_RemovePodAndEviction(t *testing.T) {
 	// Ensure hashToPods contains exactly indexerSize hashes (post-eviction and server2 removal)
 	assert.Len(t, i.hashToPods, indexerSize, "hashToPods should contain %d hashes after cleanup", indexerSize)
 }
+
+func TestIndexer_ConcurrentAddRemovePod(t *testing.T) {
+	lruSize := 10
+	for iter := range 100 {
+		i := newIndexer(context.Background(), lruSize)
+		pod := Server{ServerID: ServerID{Namespace: "default", Name: "pod1"}}
+
+		var wg sync.WaitGroup
+		wg.Add(2)
+		go func() { defer wg.Done(); i.Add([]BlockHash{1, 2, 3}, pod) }()
+		go func() { defer wg.Done(); i.RemovePod(pod.ServerID) }()
+		wg.Wait()
+
+		if _, exists := i.podToLRU[pod.ServerID]; !exists {
+			for hash, pods := range i.hashToPods {
+				assert.NotContains(t, pods, pod.ServerID, "iter %d: hashToPods[%v] references removed pod", iter, hash)
+			}
+		}
+	}
+}