solution: terminate state sync cleanly

via karalabe's un-cherry-pickable 4cf1ece5ba7c28e9ef7edabe0f53e5ae1fe37b76

eth/downloader/downloader.go

@@ -1439,10 +1439,19 @@ func (d *Downloader) processFastSyncContent(latest *types.Header) error {
 	)
 	for {
 		// Wait for the next batch of downloaded data to be available, and if the pivot
-		// block became stale, move the goalpost.
+		// block became stale, move the goalpost
 		results := d.queue.Results(oldPivot == nil) // Block if we're not monitoring pivot staleness
-		if len(results) == 0 && oldPivot == nil {
-			return stateSync.Cancel()
+		if len(results) == 0 {
+			// If pivot sync is done, stop
+			if oldPivot == nil {
+				return stateSync.Cancel()
+			}
+			// If sync failed, stop
+			select {
+			case <-d.cancelCh:
+				return stateSync.Cancel()
+			default:
+			}
 		}
 		if d.chainInsertHook != nil {
 			d.chainInsertHook(results)

eth/downloader/statesync.go

@@ -294,6 +294,9 @@ func (s *stateSync) loop() error {
 		case <-s.cancel:
 			return errCancelStateFetch
 
+		case <-s.d.cancelCh:
+			return errCancelStateFetch
+
 		case req := <-s.deliver:
 			// Response, disconnect or timeout triggered, drop the peer if stalling
 			glog.V(logger.Debug).Infoln("Received node data response", "peer", req.peer.id, "count", len(req.response), "dropped", req.dropped, "timeout", !req.dropped && req.timedOut())
@@ -348,6 +351,7 @@ func (s *stateSync) assignTasks() {
 			case s.d.trackStateReq <- req:
 				req.peer.FetchNodeData(req.items)
 			case <-s.cancel:
+			case <-s.d.cancelCh:
 			}
 		}
 	}