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WIP: alternative option for fixing race condition in requestEngineStatusAndWaitForStopped

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This commit is contained in:
James Sanderson 2025-10-03 23:47:35 +01:00
parent 0e07048006
commit f4094c301f
1 changed files with 11 additions and 18 deletions
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29
ipn/ipnlocal/local.go
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@ -2200,12 +2200,12 @@ func (b *LocalBackend) resolveExitNodeIPLocked(prefs *ipn.Prefs) (prefsChanged b
func (b *LocalBackend) setWgengineStatus(s *wgengine.Status, err error) {
if err != nil {
b.logf("wgengine status error: %v", err)
b.broadcastStatusChanged()
b.maybeBroadcastStatusChanged(nil)
return
}
if s == nil {
b.logf("[unexpected] non-error wgengine update with status=nil: %v", s)
b.broadcastStatusChanged()
b.maybeBroadcastStatusChanged(nil)
return
}
@ -2214,6 +2214,7 @@ func (b *LocalBackend) setWgengineStatus(s *wgengine.Status, err error) {
// Don't process a status update that is older than the one we have
// already processed. (corp#2579)
b.mu.Unlock()
b.maybeBroadcastStatusChanged(s)
return
}
b.lastStatusTime = s.AsOf
@ -2232,12 +2233,15 @@ func (b *LocalBackend) setWgengineStatus(s *wgengine.Status, err error) {
}
b.stateMachine()
}
b.broadcastStatusChanged()
b.maybeBroadcastStatusChanged(s)
b.send(ipn.Notify{Engine: &es})
}
// broadcastStatusChanged must not be called with b.mu held.
func (b *LocalBackend) broadcastStatusChanged() {
// maybeBroadcastStatusChanged must not be called with b.mu held.
func (b *LocalBackend) maybeBroadcastStatusChanged(s *wgengine.Status) {
if s != nil && (s.DERPs != 0 || len(s.Peers) != 0) {
return
}
// The sync.Cond docs say: "It is allowed but not required for the caller to hold c.L during the call."
// In this particular case, we must acquire b.mu. Otherwise we might broadcast before
// the waiter (in requestEngineStatusAndWait) starts to wait, in which case
@ -5696,19 +5700,8 @@ func (b *LocalBackend) requestEngineStatusAndWaitForStopped() {
b.goTracker.Go(b.e.RequestStatus)
b.logf("requestEngineStatusAndWaitForStopped: waiting...")
for {
b.statusChanged.Wait() // temporarily releases lock while waiting
if !b.blocked {
b.logf("requestEngineStatusAndWaitForStopped: engine is no longer blocked, must have stopped and started again, not safe to wait.")
break
}
if b.engineStatus.NumLive == 0 && b.engineStatus.LiveDERPs == 0 {
b.logf("requestEngineStatusAndWaitForStopped: engine is stopped.")
break
}
b.logf("requestEngineStatusAndWaitForStopped: engine is still running. Waiting...")
}
b.statusChanged.Wait() // temporarily releases lock while waiting
b.logf("requestEngineStatusAndWaitForStopped: engine was stopped.")
}
// setControlClientLocked sets the control client to cc,