The 'Before' dependency between NM-dispatcher and NM causes a deadlock
when stopping the NM service. When terminating, NM wants to D-Bus
activate NM-dispatcher to synchronously handle pre-down events; but
NM-dispatcher start is ordered after NM shutdown due to the following
behavior described in systemd.unit(5) man page:
Given two units with any ordering dependency between them, if one
unit is shut down and the other is started up, the shutdown is
ordered before the start-up. It doesn't matter if the ordering
dependency is After= or Before=, in this case. It also doesn't
matter which of the two is shut down, as long as one is shut down
and the other is started up; the shutdown is ordered before the
start-up in all cases.
So, NM is waiting NM-dispatcher to start and NM-dispatcher is queued
by systemd, waiting that NM is stopped. The result is a 90 seconds
delay, after which systemd kills NM and continues.
The dependency was added so that during shutdown NM-dispatcher would
be stopped after NM. I don't think it worked as expected because
NM-dispatcher is not supposed to be active most of the times, and so
it doesn't need a dependency that delays its stop after NM.
This reverts commit acc335aad4.
During shutdown, systemd should first stop NetworkManager and then
the dispatcher service. Note that dispatcher service is D-Bus activated,
so the two services don't Want/Require each other. But the ordering
still matters.
You're supposed to be able to use dispatcher scripts to spawn
long-running processes, but currently systemd will kill them when
nm-dispatcher exits. Fix that.
https://bugzilla.gnome.org/show_bug.cgi?id=725492
Lennart sez:
"Oh, I wasn't aware it is short-lived only. In that case, drop the
multi-user.target bit, and just make it create the dbus alias.
[Install]
Alias=dbus-org.freedesktop.nm-dispatcher.service
And yeah, adding Also=NetworkManager-dispatcher.service to
NetworkManager.service certainly would be a good idea."
