@ddstreet I opened a separate ticket as requested a while ago. Some eyes
on it would be very welcome. It's bug 1759573

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  ifup -a does not start dependants last, causes deadlocks with

Status in ifupdown package in Ubuntu:
Status in ifupdown source package in Xenial:

Bug description:
  This is a problem I've been struggling with since moving to 16.04.1
  from 14.04 (fresh install)

  I don't believe this problem affected 14.04. I have used an almost
  identical interfaces file on 14.04 without problem.

  On 16.04.1, however, 9/10 boots would hang during network
  configuration and leave the network incorrectly configured.

  When calling "ifup -a" all candidate interfaces appear to be started
  in parallel leading to collisions with locks. This causes hanging
  (until timeout) during booting and the network interfaces left
  incorrectly configured

  Imagine this /etc/network/interfaces

  auto eno1 bond0 bond0.1

  iface eno1 inet manual
          bond-master     bond0

  iface bond0 inet manual
          bond-slaves     eno1
          bond-mode       4
          bond-lacp-rate  1
          bond-miimon     100
          bond-updelay    200
          bond-downdelay  200

  iface bond0.5 inet dhcp
          vlan-raw-device bond0

  eno1 -> bond0 -> bond0.5 -> dhcp

  When calling "ifup -a" at boot time all three interfaces are started
  at the same time.

  bond0 and bond0.5 both attempt to share the same lock file:


  If bond0 wins the race, the system will start correctly (1/10):

    * bond0 starts and creates the bond0 device and the ifenslave.bond0 file to 
indicate the bond is ready
    * eno1 polls for the ifenslave.bond0 file, when it appears it attaches eno1 
to bond0
    * bond0 finishes and releases the lock
    * bond0.5 now acquires the lock.
    * bond0.5 starts dhclient, which can talk to the network and configure the 

  If, however, bond0.2 wins the lock race, the system will hang at boot (5 
mins) and fail to set up the network.

    * bond0.5 is awarded the ifstate.bond0 lockfile
    * bond0.5 starts dhclient waiting to hear from the network
    * bond0 is blocked, so bond0 is not created nor is the bond0.ifenslave file 
    * eno1 polls but never finds the ifenslave.bond0 file so never attaches to 
    * bond0.5's dhclient is trying to talk to a disconnected network and never 
receives an answer

    ! bond0.5 is stuck running dhclient
    ! bond0 is stuck waiting for bond0.5 to finish
    ! eno1 is stuck waiting for bond0 to create the ifenslave.bond0 file

  I believe ifup should start interfaces (that share lock files) in dependant 
order. The most basic interface must be awarded the lock over its dependants. 
In this case:
    1 eno1
    2 bond0
    3 bond0.5

  but never:

    1 eno1
    2 bond0.5
    3 bond0

  As a work arouund, in /etc/network/interfaces

  -auto       eno1 bond0 bond0.1
  +auto       eno1 bond0
  +allow-bond bond0.1

  And also in /lib/systemd/system/networking.service

   ExecStart=/sbin/ifup -a --read-environment
  +ExecStart=/sbin/ifup -a --allow=bond --read-environment
   ExecStop=/sbin/ifdown -a --read-environment

  Then run:

    systemctl dameon-reload

  This causes all "auto" interfaces to start then, when they've
  completed, all allow-bond interfaces to start.

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: ifupdown 0.8.10ubuntu1.1 [modified: 
  ProcVersionSignature: Ubuntu 4.4.0-45.66-generic 4.4.21
  Uname: Linux 4.4.0-45-generic x86_64
  ApportVersion: 2.20.1-0ubuntu2.1
  Architecture: amd64
  Date: Wed Oct 26 06:32:57 2016
  InstallationDate: Installed on 2016-10-24 (1 days ago)
  InstallationMedia: Ubuntu-Server 16.04.1 LTS "Xenial Xerus" - Release amd64 
  SourcePackage: ifupdown
  UpgradeStatus: No upgrade log present (probably fresh install)
  modified.conffile..etc.init.networking.conf: [modified]
  mtime.conffile..etc.init.networking.conf: 2016-10-26T04:52:05.750927

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