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.
105abf27c1