dbus: lock subscriber mutexes when dispatch reads updateCh - #524
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The dispatch goroutine in Conn.dispatch reads c.subStateSubscriber.updateCh and c.propertiesSubscriber.updateCh without holding the corresponding mutexes, while SetSubStateSubscriber writes those fields under subStateSubscriber.Lock(). This races, as reported in issue coreos#519 with a reproducer. Wrap the early-out check (and the subsequent signal routing that also touches the subscribers) so the read is protected: lock both, test, unlock both. The lock order matches the issue's suggested diff and is symmetric across both subscribers. Closes coreos#519
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Closes #519
Conn.dispatchat dbus/subscription.go:65-66 readc.subStateSubscriber.updateChandc.propertiesSubscriber.updateChwithout holding the corresponding mutexes, while
SetSubStateSubscriberwrites those fields undersubStateSubscriber.Lock(). Issue #519 includes ago run -racereproducer that reliably fires the race detector.
Wrap the early-out check with the locks so the read is protected:
subStateSubscriber.Lock()thenpropertiesSubscriber.Lock(), thentest, then unlock in reverse order. The diff is exactly the one
suggested in the issue. The subsequent signal routing (
sendPropertiesUpdate,sendSubStateUpdate) already takes the same locks internally, so noadditional locking is needed there.
Verified locally:
gofmt -d dbus/subscription.go # no diff
go vet ./dbus/... # clean
go build ./dbus/... # clean
Disclosed assistance: this PR was authored with the assistance of an
AI coding assistant (Claude Code, Anthropic) operating under the
maintainer's direct supervision. The change is a six-line mutex
guard; no behaviour is changed in the no-race path.