Package: python3-dbusmock
Version: 0.34.3-1
Severity: important
Tags: unreproducible
Control: affects -1 + src:mutter
User: [email protected]
Usertags: flaky

After my recent upload of mutter 48.4-2 to unstable, its autopkgtest
failed on ppc64el. At least one of the failures (monitor-unit.test) had
this logged, and the test subsequently timed out:

https://ci.debian.net/packages/m/mutter/testing/ppc64el/62167381/ https://ci.debian.net/data/autopkgtest/testing/ppc64el/m/mutter/62167381/artifacts.tar.gz

Starting mocked services...
Traceback (most recent call last):
File "/usr/libexec/installed-tests/mutter-16/mutter-installed-dbus-session.py", line 22, in <module>
result = meta_run(MutterDBusRunner,
extra_env=extra_env,
setup_argparse=add_extra_args,
handle_argparse=handle_extra_args)
File "/usr/share/mutter-16/tests/mutter_dbusrunner.py", line 325, in meta_run
return run_test_mocked(klass, rest,
launch=args.launch,
bind_sockets=True,
extra_env=extra_env)
File "/usr/share/mutter-16/tests/mutter_dbusrunner.py", line 271, in run_test_mocked
klass.setUpClass(launch=launch,
~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^
bind_sockets=bind_sockets)
^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/share/mutter-16/tests/mutter_dbusrunner.py", line 67, in setUpClass
(klass.mocks_manager, klass.mock_obj) = klass.start_from_local_template(
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
'meta-mocks-manager', {'templates-dir': klass.__get_templates_dir()})
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/share/mutter-16/tests/mutter_dbusrunner.py", line 119, in start_from_local_template
return klass.start_from_template(template, params, system_bus=system_bus)
~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/share/mutter-16/tests/mutter_dbusrunner.py", line 108, in start_from_template
klass.spawn_server_template(template,
~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^
params,
^^^^^^^
get_subprocess_stdout(),
^^^^^^^^^^^^^^^^^^^^^^^^
system_bus=system_bus)
^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3/dist-packages/dbusmock/testcase.py", line 438, in spawn_server_template
server = SpawnedMock.spawn_with_template(template, parameters, bustype, stdout, stderr=None)
File "/usr/lib/python3/dist-packages/dbusmock/testcase.py", line 614, in spawn_with_template
server = SpawnedMock.spawn_for_name(module.BUS_NAME, module.MAIN_OBJ, interface_name, bustype, stdout, stderr)
File "/usr/lib/python3/dist-packages/dbusmock/testcase.py", line 557, in spawn_for_name
bus = bustype.get_connection()
File "/usr/lib/python3/dist-packages/dbusmock/testcase.py", line 58, in get_connection
return dbus.bus.BusConnection(val)
~~~~~~~~~~~~~~~~~~~~~~^^^^^
File "/usr/lib/python3/dist-packages/dbus/bus.py", line 120, in __new__
bus = cls._new_for_bus(address_or_type, mainloop=mainloop) dbus.exceptions.DBusException: org.freedesktop.DBus.Error.NoServer: Failed to connect to socket /tmp/dbusmock_data_nh20oy7q/system_bus.socket: Connection refused

I think this indicates that dbusmock started a dbus-daemon to be the
mock system bus, but then attempted to connect to the socket before the dbus-daemon was listening on that socket. There is a (very) short window
of time between bind() and listen() during which connection attempts
will fail.

If my theory is correct, this will be difficult to reproduce on-demand:
you would have to be very unlucky with how processes get scheduled.

dbus-daemon provides two mechanisms to avoid this race condition window:

1. If you run it with --print-address=FD and/or --print-pid=FD, and then
read until EOF on the given file descriptor(s) (often 1 for stdout, but
may be any writeable fd), then the read will block until after the
dbus-daemon has called listen(), closing the race condition. This is how dbus-run-session(1) is implemented.

2. Or, if you run it with --fork, it will "daemonize" and the foreground process will not exit until the background process has called listen().
This is how dbus-launch(1) is implemented.

I would recommend (1.), blocking on a read() until --print-address or --print-pid has produced its result (you can ignore the printed address
or pid if you don't need it). For example test/gvfs-test in
gvfs_1.57.2-2 and tests/test-dconf.py in dconf_0.40.0-5 both do this, in
a way that should be compatible with dbusmock's use of subprocess.Popen.

Thanks,
smcv

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