libnetwork: "cannot accept client connections" on shutdown

[thaJeztah]

Not a critical issue, but when working on https://github.com/moby/moby/pull/42835/files#r713120315, I noticed that an error is printed on every shutdown of the daemon;

time="2021-09-21T12:55:04.290097255Z" level=info msg="API listen on /tmp/docker-integration/d9ac12b0678f4.sock"
time="2021-09-21T12:55:04.414946112Z" level=debug msg="Calling GET /_ping"
time="2021-09-21T12:55:04.415317278Z" level=debug msg="Calling GET /info"
time="2021-09-21T12:55:04.430754586Z" level=info msg="Got signal to reload configuration, reloading from: /etc/docker/daemon.json"
time="2021-09-21T12:55:04.431178648Z" level=debug msg="Reset Max Concurrent Downloads: 3"
time="2021-09-21T12:55:04.431201851Z" level=debug msg="Reset Max Concurrent Uploads: 5"
time="2021-09-21T12:55:04.431221426Z" level=debug msg="Reset Max Download Attempts: 5"
time="2021-09-21T12:55:04.432309643Z" level=info msg="Reloaded configuration: {\"storage-driver\":\"overlay2\",\"mtu\":1500,\"pidfile\":\"/go/src/github.com/docker/docker/bundles/test-integration-flaky/TestDaemonProxy/reload_sanitized/d9ac12b0678f4/docker.pid\",\"data-root\":\"/go/src/github.com/docker/docker/bundles/test-integration-flaky/TestDaemonProxy/reload_sanitized/d9ac12b0678f4/root\",\"exec-root\":\"/tmp/dxr/d9ac12b0678f4\",\"group\":\"docker\",\"deprecated-key-path\":\"/etc/docker/key.json\",\"max-concurrent-downloads\":3,\"max-concurrent-uploads\":5,\"max-download-attempts\":5,\"shutdown-timeout\":15,\"debug\":true,\"hosts\":[\"unix:///tmp/docker-integration/d9ac12b0678f4.sock\"],\"log-level\":\"info\",\"swarm-default-advertise-addr\":\"\",\"swarm-raft-heartbeat-tick\":0,\"swarm-raft-election-tick\":0,\"metrics-addr\":\"\",\"host-gateway-ip\":\"172.18.0.1\",\"log-driver\":\"json-file\",\"ip\":\"0.0.0.0\",\"icc\":true,\"iptables\":true,\"ip-forward\":true,\"ip-masq\":true,\"userland-proxy\":true,\"default-address-pools\":{\"Values\":null},\"network-control-plane-mtu\":1500,\"experimental\":false,\"containerd\":\"/var/run/docker/containerd/containerd.sock\",\"builder\":{\"GC\":{},\"Entitlements\":{}},\"containerd-namespace\":\"d9ac12b0678f4\",\"containerd-plugin-namespace\":\"d9ac12b0678f4p\",\"runtimes\":{\"io.containerd.runc.v2\":{\"path\":\"runc\"},\"io.containerd.runtime.v1.linux\":{\"path\":\"runc\"},\"runc\":{\"path\":\"runc\"}},\"default-runtime\":\"runc\",\"seccomp-profile\":\"builtin\",\"default-shm-size\":67108864,\"default-ipc-mode\":\"private\",\"default-cgroupns-mode\":\"host\",\"resolv-conf\":\"/etc/resolv.conf\",\"http-proxy\":\"https://xxxxx:xxxxx@example.org\",\"https-proxy\":\"https://xxxxx:xxxxx@example.org\",\"no-proxy\":\"example.com\"}"
time="2021-09-21T12:55:04.435328719Z" level=info msg="Processing signal 'interrupt'"
time="2021-09-21T12:55:04.435439253Z" level=debug msg="daemon configured with a 15 seconds minimum shutdown timeout"
time="2021-09-21T12:55:04.435514624Z" level=debug msg="start clean shutdown of all containers with a 15 seconds timeout..."
time="2021-09-21T12:55:04.435590112Z" level=debug msg="found 0 orphan layers"
time="2021-09-21T12:55:04.437848674Z" level=debug msg="Unix socket /tmp/dxr/d9ac12b0678f4/libnetwork/f7725651065a.sock doesn't exist. cannot accept client connections"
time="2021-09-21T12:55:04.437938435Z" level=debug msg="Cleaning up old mountid : start."
time="2021-09-21T12:55:04.439961024Z" level=debug msg="Cleaning up old mountid : done."
time="2021-09-21T12:55:04.444201003Z" level=debug msg="Clean shutdown succeeded"
time="2021-09-21T12:55:04.444236880Z" level=info msg="Daemon shutdown complete"

Checking logs of that test-run, it looks to be occurring in all tests that shutdown the daemon (running within the bundles top level directory);

grep -lr 'cannot accept client connections' . | wc -l
     419

The error is produced in controller.acceptClientConnections

moby/libnetwork/sandbox_externalkey_unix.go

Lines 142 to 147 in 085c6a9

	func (c *controller) acceptClientConnections(sock string, l net.Listener) {
	for {
	conn, err := l.Accept()
	if err != nil {
	if _, err1 := os.Stat(sock); os.IsNotExist(err1) {
	logrus.Debugf("Unix socket %s doesn't exist. cannot accept client connections", sock)

Which is called by controller.startExternalKeyListener(), which is called by libnetwork/New(), which is called by daemon.initNetworkController(), which is called by daemon.restore() (need to follow the code further where that's called)