les: fix fetcher syncing logic (#18072)

les/fetcher.go

@@ -143,21 +143,21 @@ func (f *lightFetcher) syncLoop() {
 			var (
 				rq      *distReq
 				reqID   uint64
+				syncing bool
 			)
 			if !f.syncing && !(newAnnounce && s) {
-				rq, reqID = f.nextRequest()
+				rq, reqID, syncing = f.nextRequest()
 			}
-			syncing := f.syncing
 			f.lock.Unlock()
 
 			if rq != nil {
 				requesting = true
-				_, ok := <-f.pm.reqDist.queue(rq)
-				if !ok {
-					f.requestChn <- false
-				}
-
-				if !syncing {
+				if _, ok := <-f.pm.reqDist.queue(rq); ok {
+					if syncing {
+						f.lock.Lock()
+						f.syncing = true
+						f.lock.Unlock()
+					} else {
 						go func() {
 							time.Sleep(softRequestTimeout)
 							f.reqMu.Lock()
@@ -171,6 +171,9 @@ func (f *lightFetcher) syncLoop() {
 							f.requestChn <- false
 						}()
 					}
+				} else {
+					f.requestChn <- false
+				}
 			}
 		case reqID := <-f.timeoutChn:
 			f.reqMu.Lock()
@@ -209,6 +212,7 @@ func (f *lightFetcher) syncLoop() {
 			f.checkSyncedHeaders(p)
 			f.syncing = false
 			f.lock.Unlock()
+			f.requestChn <- false
 		}
 	}
 }
@@ -405,7 +409,7 @@ func (f *lightFetcher) requestedID(reqID uint64) bool {
 
 // nextRequest selects the peer and announced head to be requested next, amount
 // to be downloaded starting from the head backwards is also returned
-func (f *lightFetcher) nextRequest() (*distReq, uint64) {
+func (f *lightFetcher) nextRequest() (*distReq, uint64, bool) {
 	var (
 		bestHash   common.Hash
 		bestAmount uint64
@@ -427,14 +431,12 @@ func (f *lightFetcher) nextRequest() (*distReq, uint64) {
 		}
 	}
 	if bestTd == f.maxConfirmedTd {
-		return nil, 0
+		return nil, 0, false
 	}
 
-	f.syncing = bestSyncing
-
 	var rq *distReq
 	reqID := genReqID()
-	if f.syncing {
+	if bestSyncing {
 		rq = &distReq{
 			getCost: func(dp distPeer) uint64 {
 				return 0
@@ -500,7 +502,7 @@ func (f *lightFetcher) nextRequest() (*distReq, uint64) {
 			},
 		}
 	}
-	return rq, reqID
+	return rq, reqID, bestSyncing
 }
 
 // deliverHeaders delivers header download request responses for processing