eth, triedb: ignore duplicated beacon header

eth/downloader/beaconsync.go

@@ -86,6 +86,7 @@ func (b *beaconBackfiller) resume() {
 		// If a previous filling cycle is still running, just ignore this start
 		// request. // TODO(karalabe): We should make this channel driven
 		b.lock.Unlock()
+		log.Debug("Backfiller is running")
 		return
 	}
 	b.filling = true

eth/downloader/skeleton.go

@@ -675,9 +675,19 @@ func (s *skeleton) processNewHead(head *types.Header, final *types.Header) error
 		// Not a noop / double head announce, abort with a reorg
 		return fmt.Errorf("%w, tail: %d, head: %d, newHead: %d", errChainReorged, lastchain.Tail, lastchain.Head, number)
 	}
+	// Terminate the sync if the chain head is gapped
 	if lastchain.Head+1 < number {
 		return fmt.Errorf("%w, head: %d, newHead: %d", errChainGapped, lastchain.Head, number)
 	}
+	// Ignore the duplicated beacon header announcement
+	if lastchain.Head == number {
+		local := rawdb.ReadSkeletonHeader(s.db, number)
+		if local != nil && local.Hash() == head.Hash() {
+			log.Debug("Ignored the identical beacon header", "number", number, "hash", local.Hash())
+			return nil
+		}
+	}
+	// Terminate the sync if the chain head is forked
 	if parent := rawdb.ReadSkeletonHeader(s.db, number-1); parent.Hash() != head.ParentHash {
 		return fmt.Errorf("%w, ancestor: %d, hash: %s, want: %s", errChainForked, number-1, parent.Hash(), head.ParentHash)
 	}

triedb/pathdb/generate.go

@@ -148,6 +148,7 @@ func (g *generator) stop() {
 	g.abort <- ch
 	<-ch
 	g.running = false
+	log.Debug("Snapshot generation has been terminated")
 }
 
 // completed returns the flag indicating if the whole generation is done.