Fix a regression in prefix plugin which can cause data race (#1188)

Author: liu-cong

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

@@ -85,13 +85,14 @@ func (i *indexer) Get(hash BlockHash) podSet {
 	i.mu.RLock()
 	defer i.mu.RUnlock()
 
-	res := podSet{}
-	pods, ok := i.hashToPods[hash]
-	if !ok {
-		return res
+	pods := i.hashToPods[hash]
+	res := make(podSet, len(pods))
+	for pod := range pods {
+		// Deep copy to avoid race condition.
+		res[pod] = struct{}{}
 	}
 
-	return pods
+	return res
 }
 
 // makeEvictionFn returns a per-pod LRU eviction callback that removes the pod from hashToPods on eviction.

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

@@ -41,4 +41,7 @@ func TestIndexer_AddAndGet(t *testing.T) {
 	// Add another entry to the cache, which should evict the first one due to max size.
 	i.Add([]BlockHash{BlockHash(3)}, server)
 	assert.Equal(t, 2, i.podToLRU[server].Len(), "Cache size should still be 2 after adding an entry")
+
+	servers = i.Get(BlockHash(4))
+	assert.Empty(t, servers, "Cache should not contain non-existent hash")
 }