device: use channel close to shut down and drain decryption channel

This is similar to commit e1fa1cc5560020e67d33aa7e74674853671cf0a0,
but for the decryption channel.

It is an alternative fix to f9f655567930a4cd78d40fa4ba0d58503335ae6a.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

1 files changed, 25 insertions, 12 deletions

diff --git a/device/device.go b/device/device.go
index d37fe6f..9a9b1b3 100644
--- a/device/device.go
+++ b/device/device.go
@@ -76,7 +76,7 @@ type Device struct {
 
 	queue struct {
 		encryption *encryptionQueue
-		decryption chan *QueueInboundElement
+		decryption *decryptionQueue
 		handshake  chan QueueHandshakeElement
 	}
 
@@ -115,6 +115,24 @@ func newEncryptionQueue() *encryptionQueue {
 	return q
 }
 
+// A decryptionQueue is similar to an encryptionQueue; see those docs.
+type decryptionQueue struct {
+	c  chan *QueueInboundElement
+	wg sync.WaitGroup
+}
+
+func newDecryptionQueue() *decryptionQueue {
+	q := &decryptionQueue{
+		c: make(chan *QueueInboundElement, QueueInboundSize),
+	}
+	q.wg.Add(1)
+	go func() {
+		q.wg.Wait()
+		close(q.c)
+	}()
+	return q
+}
+
 /* Converts the peer into a "zombie", which remains in the peer map,
  * but processes no packets and does not exists in the routing table.
  *
@@ -308,7 +326,7 @@ func NewDevice(tunDevice tun.Device, logger *Logger) *Device {
 
 	device.queue.handshake = make(chan QueueHandshakeElement, QueueHandshakeSize)
 	device.queue.encryption = newEncryptionQueue()
-	device.queue.decryption = make(chan *QueueInboundElement, QueueInboundSize)
+	device.queue.decryption = newDecryptionQueue()
 
 	// prepare signals
 
@@ -369,13 +387,6 @@ func (device *Device) RemoveAllPeers() {
 func (device *Device) FlushPacketQueues() {
 	for {
 		select {
-		case elem, ok := <-device.queue.decryption:
-			if ok {
-				if !elem.IsDropped() {
-					elem.Drop()
-					device.PutMessageBuffer(elem.buffer)
-				}
-			}
 		case <-device.queue.handshake:
 		default:
 			return
@@ -399,10 +410,11 @@ func (device *Device) Close() {
 
 	device.isUp.Set(false)
 
-	// We kept a reference to the encryption queue,
-	// in case we started any new peers that might write to it.
-	// No new peers are coming; we are done with the encryption queue.
+	// We kept a reference to the encryption and decryption queues,
+	// in case we started any new peers that might write to them.
+	// No new peers are coming; we are done with these queues.
 	device.queue.encryption.wg.Done()
+	device.queue.decryption.wg.Done()
 	close(device.signals.stop)
 	device.state.stopping.Wait()
 
@@ -549,6 +561,7 @@ func (device *Device) BindUpdate() error {
 		// start receiving routines
 
 		device.net.stopping.Add(2)
+		device.queue.decryption.wg.Add(2) // each RoutineReceiveIncoming goroutine writes to device.queue.decryption
 		go device.RoutineReceiveIncoming(ipv4.Version, netc.bind)
 		go device.RoutineReceiveIncoming(ipv6.Version, netc.bind)