device: separate timersInit from timersStart

timersInit sets up the timers.
It need only be done once per peer.

timersStart does the work to prepare the timers
for a newly running peer. It needs to be done
every time a peer starts.

Separate the two and call them in the appropriate places.
This prevents data races on the peer's timers fields
when starting and stopping peers.

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

device/peer.go

@@ -107,6 +107,7 @@ func (device *Device) NewPeer(pk NoisePublicKey) (*Peer, error) {
 	device.peers.empty.Set(false)
 
 	// start peer
+	peer.timersInit()
 	if peer.device.isUp() {
 		peer.Start()
 	}
@@ -183,7 +184,7 @@ func (peer *Peer) Start() {
 	}
 	peer.device.queue.encryption.wg.Add(1) // keep encryption queue open for our writes
 
-	peer.timersInit()
+	peer.timersStart()
 
 	go peer.RoutineSequentialSender()
 	go peer.RoutineSequentialReceiver()

device/timers.go

@@ -14,10 +14,8 @@ import (
 	"time"
 )
 
-/* This Timer structure and related functions should roughly copy the interface of
- * the Linux kernel's struct timer_list.
- */
-
+// A Timer manages time-based aspects of the WireGuard protocol.
+// Timer roughly copies the interface of the Linux kernel's struct timer_list.
 type Timer struct {
 	*time.Timer
 	modifyingLock sync.RWMutex
@@ -213,6 +211,9 @@ func (peer *Peer) timersInit() {
 	peer.timers.newHandshake = peer.NewTimer(expiredNewHandshake)
 	peer.timers.zeroKeyMaterial = peer.NewTimer(expiredZeroKeyMaterial)
 	peer.timers.persistentKeepalive = peer.NewTimer(expiredPersistentKeepalive)
+}
+
+func (peer *Peer) timersStart() {
 	atomic.StoreUint32(&peer.timers.handshakeAttempts, 0)
 	peer.timers.sentLastMinuteHandshake.Set(false)
 	peer.timers.needAnotherKeepalive.Set(false)