From a9340d22c4cb6960168df947fdc963365d975644 Mon Sep 17 00:00:00 2001
From: Olaoluwa Osuntokun <laolu32@gmail.com>
Date: Mon, 4 Jun 2018 16:43:53 -0700
Subject: [PATCH 1/3] discovery: ensure stopping/starting a gossipSyncer is
 idempotent

---
 discovery/syncer.go | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/discovery/syncer.go b/discovery/syncer.go
index 85e356bca..a187c7ef2 100644
--- a/discovery/syncer.go
+++ b/discovery/syncer.go
@@ -175,6 +175,9 @@ type gossipSyncerCfg struct {
 //
 // TODO(roasbeef): modify to only sync from one peer at a time?
 type gossipSyncer struct {
+	started uint32
+	stopped uint32
+
 	// remoteUpdateHorizon is the update horizon of the remote peer. We'll
 	// use this to properly filter out any messages.
 	remoteUpdateHorizon *lnwire.GossipTimestampRange
@@ -226,6 +229,10 @@ func newGossiperSyncer(cfg gossipSyncerCfg) *gossipSyncer {
 // Start starts the gossipSyncer and any goroutines that it needs to carry out
 // its duties.
 func (g *gossipSyncer) Start() error {
+	if !atomic.CompareAndSwapUint32(&g.started, 0, 1) {
+		return nil
+	}
+
 	log.Debugf("Starting gossipSyncer(%x)", g.peerPub[:])
 
 	g.wg.Add(1)
@@ -237,6 +244,10 @@ func (g *gossipSyncer) Start() error {
 // Stop signals the gossipSyncer for a graceful exit, then waits until it has
 // exited.
 func (g *gossipSyncer) Stop() error {
+	if !atomic.CompareAndSwapUint32(&g.stopped, 0, 1) {
+		return nil
+	}
+
 	close(g.quit)
 
 	g.wg.Wait()

From 0ec4a06e6b2e409427ac78e3b2fd95fb3f3a9e30 Mon Sep 17 00:00:00 2001
From: Olaoluwa Osuntokun <laolu32@gmail.com>
Date: Mon, 4 Jun 2018 16:50:04 -0700
Subject: [PATCH 2/3] discovery: fix deadlock by ensure we don't hold sync
 mutex during send

In this commit, we fix an existing deadlock in the
gossiper->server->peer pipeline by ensuring that we're not holding the
syncer mutex while we attempt to have a syncer filter out the rest of
gossip messages.
---
 discovery/gossiper.go | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/discovery/gossiper.go b/discovery/gossiper.go
index 878a9cd30..84af3ab5b 100644
--- a/discovery/gossiper.go
+++ b/discovery/gossiper.go
@@ -525,7 +525,7 @@ type msgWithSenders struct {
 // with peers that we have an active gossipSyncer with. We do this to ensure
 // that we don't broadcast messages to any peers that we have active gossip
 // syncers for.
-func (m *msgWithSenders) mergeSyncerMap(syncers map[routing.Vertex]struct{}) {
+func (m *msgWithSenders) mergeSyncerMap(syncers map[routing.Vertex]*gossipSyncer) {
 	for peerPub := range syncers {
 		m.senders[peerPub] = struct{}{}
 	}
@@ -1130,9 +1130,9 @@ func (d *AuthenticatedGossiper) networkHandler() {
 			// syncers, we'll collect their pubkeys so we can avoid
 			// sending them the full message blast below.
 			d.syncerMtx.RLock()
-			syncerPeers := map[routing.Vertex]struct{}{}
-			for peerPub := range d.peerSyncers {
-				syncerPeers[peerPub] = struct{}{}
+			syncerPeers := make(map[routing.Vertex]*gossipSyncer)
+			for peerPub, syncer := range d.peerSyncers {
+				syncerPeers[peerPub] = syncer
 			}
 			d.syncerMtx.RUnlock()
 
@@ -1142,11 +1142,9 @@ func (d *AuthenticatedGossiper) networkHandler() {
 			// We'll first attempt to filter out this new message
 			// for all peers that have active gossip syncers
 			// active.
-			d.syncerMtx.RLock()
-			for _, syncer := range d.peerSyncers {
+			for _, syncer := range syncerPeers {
 				syncer.FilterGossipMsgs(announcementBatch...)
 			}
-			d.syncerMtx.RUnlock()
 
 			// Next, If we have new things to announce then
 			// broadcast them to all our immediately connected
@@ -1234,8 +1232,7 @@ func (d *AuthenticatedGossiper) PruneSyncState(peer *btcec.PublicKey) {
 		peer.SerializeCompressed())
 
 	vertex := routing.NewVertex(peer)
-
-	syncer, ok := d.peerSyncers[routing.NewVertex(peer)]
+	syncer, ok := d.peerSyncers[vertex]
 	if !ok {
 		return
 	}

From e6d46f681b54d53b9cddab59bf77c6cac53b35e8 Mon Sep 17 00:00:00 2001
From: Olaoluwa Osuntokun <laolu32@gmail.com>
Date: Mon, 4 Jun 2018 17:18:48 -0700
Subject: [PATCH 3/3] discovery: if gossipSyncer is shutting down, don't filter
 messages

---
 discovery/syncer.go | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/discovery/syncer.go b/discovery/syncer.go
index a187c7ef2..d115c7234 100644
--- a/discovery/syncer.go
+++ b/discovery/syncer.go
@@ -805,6 +805,12 @@ func (g *gossipSyncer) FilterGossipMsgs(msgs ...msgWithSenders) {
 		return
 	}
 
+	// If we've been signalled to exit, or are exiting, then we'll stop
+	// short.
+	if atomic.LoadUint32(&g.stopped) == 1 {
+		return
+	}
+
 	// TODO(roasbeef): need to ensure that peer still online...send msg to
 	// gossiper on peer termination to signal peer disconnect?