device: use int64 instead of atomic.Value for time stamp

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

device/alignment_test.go

@@ -41,3 +41,27 @@ func TestPeerAlignment(t *testing.T) {
 	checkAlignment(t, "Peer.stats", unsafe.Offsetof(p.stats))
 	checkAlignment(t, "Peer.isRunning", unsafe.Offsetof(p.isRunning))
 }
+
+
+// TestDeviceAlignment checks that atomically-accessed fields are
+// aligned to 64-bit boundaries, as required by the atomic package.
+//
+// Unfortunately, violating this rule on 32-bit platforms results in a
+// hard segfault at runtime.
+func TestDeviceAlignment(t *testing.T) {
+	var d Device
+
+	typ := reflect.TypeOf(&d).Elem()
+	t.Logf("Device type size: %d, with fields:", typ.Size())
+	for i := 0; i < typ.NumField(); i++ {
+		field := typ.Field(i)
+		t.Logf("\t%30s\toffset=%3v\t(type size=%3d, align=%d)",
+			field.Name,
+			field.Offset,
+			field.Type.Size(),
+			field.Type.Align(),
+		)
+	}
+
+	checkAlignment(t, "Device.rate.underLoadUntil", unsafe.Offsetof(d.rate.underLoadUntil))
+}

device/device.go

@@ -62,7 +62,7 @@ type Device struct {
 	cookieChecker CookieChecker
 
 	rate struct {
-		underLoadUntil atomic.Value
+		underLoadUntil int64
 		limiter        ratelimiter.Ratelimiter
 	}
 
@@ -245,20 +245,15 @@ func (device *Device) Down() {
 }
 
 func (device *Device) IsUnderLoad() bool {
-
 	// check if currently under load
-
 	now := time.Now()
 	underLoad := len(device.queue.handshake.c) >= UnderLoadQueueSize
 	if underLoad {
-		device.rate.underLoadUntil.Store(now.Add(UnderLoadAfterTime))
+		atomic.StoreInt64(&device.rate.underLoadUntil, now.Add(UnderLoadAfterTime).UnixNano())
 		return true
 	}
-
 	// check if recently under load
-
+	return atomic.LoadInt64(&device.rate.underLoadUntil) > now.UnixNano()
-	until := device.rate.underLoadUntil.Load().(time.Time)
-	return until.After(now)
 }
 
 func (device *Device) SetPrivateKey(sk NoisePrivateKey) error {
@@ -327,14 +322,9 @@ func NewDevice(tunDevice tun.Device, logger *Logger) *Device {
 		mtu = DefaultMTU
 	}
 	device.tun.mtu = int32(mtu)
-
 	device.peers.keyMap = make(map[NoisePublicKey]*Peer)
-
 	device.rate.limiter.Init()
-	device.rate.underLoadUntil.Store(time.Time{})
-
 	device.indexTable.Init()
-
 	device.PopulatePools()
 
 	// create queues