The immediate motivation for this change is an observed deadlock.
1. A goroutine calls peer.Stop. That calls peer.queue.Lock().
2. Another goroutine is in RoutineSequentialReceiver.
It receives an elem from peer.queue.inbound.
3. The peer.Stop goroutine calls close(peer.queue.inbound),
close(peer.queue.outbound), and peer.stopping.Wait().
It blocks waiting for RoutineSequentialReceiver
and RoutineSequentialSender to exit.
4. The RoutineSequentialReceiver goroutine calls peer.SendStagedPackets().
SendStagedPackets attempts peer.queue.RLock().
That blocks forever because the peer.Stop
goroutine holds a write lock on that mutex.
A background motivation for this change is that it can be expensive
to have a mutex in the hot code path of RoutineSequential*.
The mutex was necessary to avoid attempting to send elems on a closed channel.
This commit removes that danger by never closing the channel.
Instead, we send a sentinel nil value on the channel to indicate
to the receiver that it should exit.
The only problem with this is that if the receiver exits,
we could write an elem into the channel which would never get received.
If it never gets received, it cannot get returned to the device pools.
To work around this, we use a finalizer. When the channel can be GC'd,
the finalizer drains any remaining elements from the channel and
restores them to the device pool.
After that change, peer.queue.RWMutex no longer makes sense where it is.
It is only used to prevent concurrent calls to Start and Stop.
Move it to a more sensible location and make it a plain sync.Mutex.
Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
package device
-import "sync"
+import (
+ "runtime"
+ "sync"
+)
// An outboundQueue is a channel of QueueOutboundElements awaiting encryption.
// An outboundQueue is ref-counted using its wg field.
}()
return q
}
+
+// newAutodrainingInboundQueue returns a channel that will be drained when it gets GC'd.
+// It is useful in cases in which is it hard to manage the lifetime of the channel.
+// The returned channel must not be closed. Senders should signal shutdown using
+// some other means, such as sending a sentinel nil values.
+func newAutodrainingInboundQueue(device *Device) chan *QueueInboundElement {
+ type autodrainingInboundQueue struct {
+ c chan *QueueInboundElement
+ }
+ q := &autodrainingInboundQueue{
+ c: make(chan *QueueInboundElement, QueueInboundSize),
+ }
+ runtime.SetFinalizer(q, func(q *autodrainingInboundQueue) {
+ for {
+ select {
+ case elem := <-q.c:
+ if elem == nil {
+ continue
+ }
+ device.PutMessageBuffer(elem.buffer)
+ device.PutInboundElement(elem)
+ default:
+ return
+ }
+ }
+ })
+ return q.c
+}
+
+// newAutodrainingOutboundQueue returns a channel that will be drained when it gets GC'd.
+// It is useful in cases in which is it hard to manage the lifetime of the channel.
+// The returned channel must not be closed. Senders should signal shutdown using
+// some other means, such as sending a sentinel nil values.
+// All sends to the channel must be best-effort, because there may be no receivers.
+func newAutodrainingOutboundQueue(device *Device) chan *QueueOutboundElement {
+ type autodrainingOutboundQueue struct {
+ c chan *QueueOutboundElement
+ }
+ q := &autodrainingOutboundQueue{
+ c: make(chan *QueueOutboundElement, QueueOutboundSize),
+ }
+ runtime.SetFinalizer(q, func(q *autodrainingOutboundQueue) {
+ for {
+ select {
+ case elem := <-q.c:
+ if elem == nil {
+ continue
+ }
+ device.PutMessageBuffer(elem.buffer)
+ device.PutOutboundElement(elem)
+ default:
+ return
+ }
+ }
+ })
+ return q.c
+}
sentLastMinuteHandshake AtomicBool
}
+ state struct {
+ mu sync.Mutex // protects against concurrent Start/Stop
+ }
+
queue struct {
- sync.RWMutex
staged chan *QueueOutboundElement // staged packets before a handshake is available
outbound chan *QueueOutboundElement // sequential ordering of udp transmission
inbound chan *QueueInboundElement // sequential ordering of tun writing
}
// prevent simultaneous start/stop operations
- peer.queue.Lock()
- defer peer.queue.Unlock()
+ peer.state.mu.Lock()
+ defer peer.state.mu.Unlock()
if peer.isRunning.Get() {
return
peer.handshake.mutex.Unlock()
// prepare queues
- peer.queue.outbound = make(chan *QueueOutboundElement, QueueOutboundSize)
- peer.queue.inbound = make(chan *QueueInboundElement, QueueInboundSize)
+ peer.queue.outbound = newAutodrainingOutboundQueue(device)
+ peer.queue.inbound = newAutodrainingInboundQueue(device)
if peer.queue.staged == nil {
peer.queue.staged = make(chan *QueueOutboundElement, QueueStagedSize)
}
}
func (peer *Peer) Stop() {
- peer.queue.Lock()
- defer peer.queue.Unlock()
+ peer.state.mu.Lock()
+ defer peer.state.mu.Unlock()
if !peer.isRunning.Swap(false) {
return
peer.device.log.Verbosef("%v - Stopping...", peer)
peer.timersStop()
-
- close(peer.queue.inbound)
- close(peer.queue.outbound)
+ // Signal that RoutineSequentialSender and RoutineSequentialReceiver should exit.
+ peer.queue.inbound <- nil
+ peer.queue.outbound <- nil
peer.stopping.Wait()
peer.device.queue.encryption.wg.Done() // no more writes to encryption queue from us
elem.Lock()
// add to decryption queues
- peer.queue.RLock()
if peer.isRunning.Get() {
peer.queue.inbound <- elem
device.queue.decryption.c <- elem
} else {
device.PutInboundElement(elem)
}
- peer.queue.RUnlock()
-
continue
// otherwise it is a fixed size & handshake related packet
device.log.Verbosef("%v - Routine: sequential receiver - started", peer)
for elem := range peer.queue.inbound {
+ if elem == nil {
+ return
+ }
var err error
elem.Lock()
if elem.packet == nil {
elem.Lock()
// add to parallel and sequential queue
- peer.queue.RLock()
if peer.isRunning.Get() {
peer.queue.outbound <- elem
peer.device.queue.encryption.c <- elem
peer.device.PutMessageBuffer(elem.buffer)
peer.device.PutOutboundElement(elem)
}
- peer.queue.RUnlock()
default:
return
}
device.log.Verbosef("%v - Routine: sequential sender - started", peer)
for elem := range peer.queue.outbound {
+ if elem == nil {
+ return
+ }
elem.Lock()
if !peer.isRunning.Get() {
// peer has been stopped; return re-usable elems to the shared pool.
projects / thirdparty / wireguard-go.git / commitdiff
