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e361126515
WGIface.Close() took w.mu and held it across w.tun.Close(). The
underlying wireguard-go device waits for its send/receive goroutines to
drain before Close() returns, and some of those goroutines re-enter
WGIface during shutdown. In particular, the userspace packet filter DNS
hook in client/internal/dns.ServiceViaMemory.filterDNSTraffic calls
s.wgInterface.GetDevice() on every packet, which also needs w.mu. With
the Close-side holding the mutex, the read goroutine blocks in
GetDevice and Close waits forever for that goroutine to exit:
goroutine N (TestDNSPermanent_updateUpstream):
WGIface.Close -> holds w.mu -> tun.Close -> sync.WaitGroup.Wait
goroutine M (wireguard read routine):
FilteredDevice.Read -> filterOutbound -> udpHooksDrop ->
filterDNSTraffic.func1 -> WGIface.GetDevice -> sync.Mutex.Lock
This surfaces as a 5 minute test timeout on the macOS Client/Unit
CI job (panic: test timed out after 5m0s, running tests:
TestDNSPermanent_updateUpstream).
Release w.mu before calling w.tun.Close(). The other Close steps
(wgProxyFactory.Free, waitUntilRemoved, Destroy) do not mutate any
fields guarded by w.mu beyond what Free() already does, so the lock
is not needed once the tun has started shutting down. A new unit test
in iface_close_test.go uses a fake WGTunDevice to reproduce the
deadlock deterministically without requiring CAP_NET_ADMIN.