Merge pull request #4066 from krasi-georgiev/race-DiscoveredLabels

add mutex for DiscoveredLabels

scrape/target.go

@@ -110,6 +110,8 @@ func (t *Target) Labels() labels.Labels {
 
 // DiscoveredLabels returns a copy of the target's labels before any processing.
 func (t *Target) DiscoveredLabels() labels.Labels {
+	t.mtx.Lock()
+	defer t.mtx.Unlock()
 	lset := make(labels.Labels, len(t.discoveredLabels))
 	copy(lset, t.discoveredLabels)
 	return lset
@@ -117,6 +119,8 @@ func (t *Target) DiscoveredLabels() labels.Labels {
 
 // SetDiscoveredLabels sets new DiscoveredLabels
 func (t *Target) SetDiscoveredLabels(l labels.Labels) {
+	t.mtx.Lock()
+	defer t.mtx.Unlock()
 	t.discoveredLabels = l
 }