fix: in the swarm move Connectedness emit after releasing conns

p2p/net/swarm/swarm.go

@@ -340,12 +340,7 @@ func (s *Swarm) addConn(tc transport.CapableConn, dir network.Direction) (*Conn,
 	}
 
 	c.streams.m = make(map[*Stream]struct{})
-	if len(s.conns.m[p]) == 0 { // first connection
-		s.emitter.Emit(event.EvtPeerConnectednessChanged{
-			Peer:          p,
-			Connectedness: network.Connected,
-		})
-	}
+	isFirstConnection := len(s.conns.m[p]) == 0
 	s.conns.m[p] = append(s.conns.m[p], c)
 
 	// Add two swarm refs:
@@ -358,6 +353,15 @@ func (s *Swarm) addConn(tc transport.CapableConn, dir network.Direction) (*Conn,
 	c.notifyLk.Lock()
 	s.conns.Unlock()
 
+	// Emit event after releasing `s.conns` lock so that a consumer can still
+	// use swarm methods that need the `s.conns` lock.
+	if isFirstConnection {
+		s.emitter.Emit(event.EvtPeerConnectednessChanged{
+			Peer:          p,
+			Connectedness: network.Connected,
+		})
+	}
+
 	s.notifyAll(func(f network.Notifiee) {
 		f.Connected(s, c)
 	})
@@ -637,25 +641,32 @@ func (s *Swarm) removeConn(c *Conn) {
 	p := c.RemotePeer()
 
 	s.conns.Lock()
-	defer s.conns.Unlock()
 
 	cs := s.conns.m[p]
+
+	if len(cs) == 1 {
+		delete(s.conns.m, p)
+		s.conns.Unlock()
+
+		// Emit event after releasing `s.conns` lock so that a consumer can still
+		// use swarm methods that need the `s.conns` lock.
+		s.emitter.Emit(event.EvtPeerConnectednessChanged{
+			Peer:          p,
+			Connectedness: network.NotConnected,
+		})
+		return
+	}
+
+	defer s.conns.Unlock()
+
 	for i, ci := range cs {
 		if ci == c {
-			if len(cs) == 1 {
-				delete(s.conns.m, p)
-				s.emitter.Emit(event.EvtPeerConnectednessChanged{
-					Peer:          p,
-					Connectedness: network.NotConnected,
-				})
-			} else {
-				// NOTE: We're intentionally preserving order.
-				// This way, connections to a peer are always
-				// sorted oldest to newest.
-				copy(cs[i:], cs[i+1:])
-				cs[len(cs)-1] = nil
-				s.conns.m[p] = cs[:len(cs)-1]
-			}
+			// NOTE: We're intentionally preserving order.
+			// This way, connections to a peer are always
+			// sorted oldest to newest.
+			copy(cs[i:], cs[i+1:])
+			cs[len(cs)-1] = nil
+			s.conns.m[p] = cs[:len(cs)-1]
 			break
 		}
 	}

p2p/net/swarm/swarm_event_test.go

@@ -64,3 +64,52 @@ func TestConnectednessEventsSingleConn(t *testing.T) {
 	checkEvent(t, sub1, event.EvtPeerConnectednessChanged{Peer: s2.LocalPeer(), Connectedness: network.NotConnected})
 	checkEvent(t, sub2, event.EvtPeerConnectednessChanged{Peer: s1.LocalPeer(), Connectedness: network.NotConnected})
 }
+
+func TestNoDeadlockWhenConsumingConnectednessEvents(t *testing.T) {
+	dialerEventBus := eventbus.NewBus()
+	dialer := swarmt.GenSwarm(t, swarmt.OptDialOnly, swarmt.EventBus(dialerEventBus))
+	defer dialer.Close()
+
+	listener := swarmt.GenSwarm(t, swarmt.OptDialOnly)
+	addrsToListen := []ma.Multiaddr{
+		ma.StringCast("/ip4/0.0.0.0/udp/0/quic-v1"),
+	}
+
+	if err := listener.Listen(addrsToListen...); err != nil {
+		t.Fatal(err)
+	}
+	listenedAddrs := listener.ListenAddresses()
+
+	dialer.Peerstore().AddAddrs(listener.LocalPeer(), listenedAddrs, time.Hour)
+
+	sub, err := dialerEventBus.Subscribe(new(event.EvtPeerConnectednessChanged))
+	require.NoError(t, err)
+
+	ctx := context.Background()
+	ctx, cancel := context.WithCancel(ctx)
+	defer cancel()
+
+	// A slow consumer
+	go func() {
+		for {
+			select {
+			case <-ctx.Done():
+				return
+			case <-sub.Out():
+				time.Sleep(100 * time.Millisecond)
+				// Do something with the swarm that needs the conns lock
+				_ = dialer.ConnsToPeer(listener.LocalPeer())
+				time.Sleep(100 * time.Millisecond)
+			}
+		}
+	}()
+
+	for i := 0; i < 10; i++ {
+		// Connect and disconnect to trigger a bunch of events
+		_, err := dialer.DialPeer(context.Background(), listener.LocalPeer())
+		require.NoError(t, err)
+		dialer.ClosePeer(listener.LocalPeer())
+	}
+
+	// The test should finish without deadlocking
+}