Fix potential race in ctx intialization

retrieval/scrape.go

@@ -130,6 +130,13 @@ func newScrapePool(cfg *config.ScrapeConfig, app storage.SampleAppender) *scrape
 	}
 }
 
+func (sp *scrapePool) init(ctx context.Context) {
+	sp.mtx.Lock()
+	defer sp.mtx.Unlock()
+
+	sp.ctx = ctx
+}
+
 // stop terminates all scrape loops and returns after they all terminated.
 func (sp *scrapePool) stop() {
 	var wg sync.WaitGroup

retrieval/targetmanager.go

@@ -224,7 +224,7 @@ func (ts *targetSet) reload(cfg *config.ScrapeConfig) {
 func (ts *targetSet) runScraping(ctx context.Context) {
 	ctx, ts.cancelScraping = context.WithCancel(ctx)
 
-	ts.scrapePool.ctx = ctx
+	ts.scrapePool.init(ctx)
 
 Loop:
 	for {