Merge pull request kubernetes#136911 from pohly/dra-e2e-data-race

DRA E2E: fix data race in test driver

Author: k8s-ci-robot

test/e2e/dra/test-driver/app/kubeletplugin.go

@@ -462,6 +462,8 @@ func (ex *ExamplePlugin) nodeUnprepareResource(ctx context.Context, claimRef kub
 
 	logger := klog.FromContext(ctx)
 
+	ex.mutex.Lock()
+	defer ex.mutex.Unlock()
 	claimID := ClaimID{Name: claimRef.Name, UID: claimRef.UID}
 	devices, ok := ex.prepared[claimID]
 	if !ok {