executor: fix data race in topn (#53593)

close #53538

pkg/executor/sortexec/topn.go

@@ -415,18 +415,19 @@ func (e *TopNExec) executeTopNWhenSpillTriggered(ctx context.Context) error {
 	// Wait for the finish of all workers
 	workersWaiter := util.WaitGroupWrapper{}
 
-	// Fetch chunks from child and put chunks into chunkChannel
-	fetcherWaiter.Run(func() {
-		e.fetchChunksFromChild(ctx)
-	})
-
 	for i := range e.spillHelper.workers {
 		worker := e.spillHelper.workers[i]
+		worker.initWorker()
 		workersWaiter.Run(func() {
 			worker.run()
 		})
 	}
 
+	// Fetch chunks from child and put chunks into chunkChannel
+	fetcherWaiter.Run(func() {
+		e.fetchChunksFromChild(ctx)
+	})
+
 	fetcherWaiter.Wait()
 	workersWaiter.Wait()
 	return nil

pkg/executor/sortexec/topn_worker.go

@@ -60,9 +60,12 @@ func newTopNWorker(
 	}
 }
 
-func (t *topNWorker) fetchChunksAndProcess() {
+func (t *topNWorker) initWorker() {
 	// Offset of heap in worker should be 0, as we need to spill all data
 	t.chkHeap.init(t.topn, t.memTracker, t.topn.Limit.Offset+t.topn.Limit.Count, 0, t.topn.greaterRow, t.topn.RetFieldTypes())
+}
+
+func (t *topNWorker) fetchChunksAndProcess() {
 	for t.fetchChunksAndProcessImpl() {
 	}
 }