fix: two different scanner update races (#12615)

cmd/erasure.go

@@ -484,11 +484,11 @@ func (er erasureObjects) nsScanner(ctx context.Context, buckets []BucketInfo, bf
 				updates := make(chan dataUsageEntry, 1)
 				var wg sync.WaitGroup
 				wg.Add(1)
-				go func() {
+				go func(name string) {
 					defer wg.Done()
 					for update := range updates {
 						bucketResults <- dataUsageEntryInfo{
-							Name:   cache.Info.Name,
+							Name:   name,
 							Parent: dataUsageRoot,
 							Entry:  update,
 						}
@@ -496,7 +496,7 @@ func (er erasureObjects) nsScanner(ctx context.Context, buckets []BucketInfo, bf
 							console.Debugln("bucket", bucket.Name, "got update", update)
 						}
 					}
-				}()
+				}(cache.Info.Name)
 
 				// Calc usage
 				before := cache.Info.LastUpdate

cmd/storage-rest-server.go

@@ -188,6 +188,7 @@ func (s *storageRESTServer) NSScannerHandler(w http.ResponseWriter, r *http.Requ
 		defer wg.Done()
 		for update := range updates {
 			// Write true bool to indicate update.
+			var err error
 			if err = respW.WriteBool(true); err == nil {
 				err = update.EncodeMsg(respW)
 			}
@@ -211,6 +212,10 @@ func (s *storageRESTServer) NSScannerHandler(w http.ResponseWriter, r *http.Requ
 	if err = respW.WriteBool(false); err == nil {
 		err = usageInfo.EncodeMsg(respW)
 	}
+	if err != nil {
+		resp.CloseWithError(err)
+		return
+	}
 	resp.CloseWithError(respW.Flush())
 }