core: fix datarace in MergeLabels (#7537) (#7826)

close #7535

Co-authored-by: lhy1024 <[email protected]>
Co-authored-by: Ryan Leung <[email protected]>
Co-authored-by: ti-chi-bot[bot] <108142056+ti-chi-bot[bot]@users.noreply.github.com>

server/core/store.go

@@ -522,22 +522,37 @@ func DistinctScore(labels []string, stores []*StoreInfo, other *StoreInfo) float
 	return score
 }
 
-// MergeLabels merges the passed in labels with origins, overriding duplicated
-// ones.
+// MergeLabels merges the passed in labels with origins, overriding duplicated ones.
+// Note: To prevent potential data races, it is advisable to refrain from directly modifying the 'origin' variable.
 func (s *StoreInfo) MergeLabels(labels []*metapb.StoreLabel) []*metapb.StoreLabel {
-	storeLabels := s.GetLabels()
-L:
+	origin := s.GetLabels()
+	results := make([]*metapb.StoreLabel, 0, len(origin))
+	for _, label := range origin {
+		results = append(results, &metapb.StoreLabel{
+			Key:   label.Key,
+			Value: label.Value,
+		})
+	}
+
 	for _, newLabel := range labels {
-		for _, label := range storeLabels {
+		found := false
+		for _, label := range results {
 			if strings.EqualFold(label.Key, newLabel.Key) {
+				// Update the value for an existing key.
 				label.Value = newLabel.Value
-				continue L
+				found = true
+				break
 			}
 		}
-		storeLabels = append(storeLabels, newLabel)
+		// Add a new label if the key doesn't exist in the original slice.
+		if !found {
+			results = append(results, newLabel)
+		}
 	}
-	res := storeLabels[:0]
-	for _, l := range storeLabels {
+
+	// Filter out labels with an empty value.
+	res := results[:0]
+	for _, l := range results {
 		if l.Value != "" {
 			res = append(res, l)
 		}