[Bug 1724523] Re: fix ifupdown deadlocking against itself

[Ubuntu Foundations Team Bug Bot]

The attachment "Do not leak the parent interface's lock." seems to be a
patch.  If it isn't, please remove the "patch" flag from the attachment,
remove the "patch" tag, and if you are a member of the ~ubuntu-
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** Tags added: patch

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https://bugs.launchpad.net/bugs/1724523

Title:
  fix ifupdown deadlocking against itself

Status in ifupdown package in Ubuntu:
  New

Bug description:
  Hi,

  First of all, thanks a lot for all the work going into Ubuntu!

  While setting up a new StorPool customer installation on a 14.04 LTS
  server, I configured a VLAN on a physical Ethernet interface and then,
  separately, a bond interface that contains the Ethernet interface.
  When I tried to reboot the machine, it hung while trying to bring the
  network interfaces down.

  I tracked it down to a problem in the way the hierarchical interface
  locking was backported from Debian's ifupdown two years ago: a VLAN
  parent interface is locked, but then only unlocked at the end of the
  function, and not at the end of the per-interface loop (in Debian's
  ifupdown, the per-interface handling is in a separate function, so the
  parent interface is unlocked at the correct time).  This leads to
  problems when another interface specified on the command line (or
  deduced if the -a option is used) has scripts that run ifdown on the
  still-locked parent interface.

  I've attached a trivial patch that should correct the issue.  It may
  be tested on e.g. a virtual machine with the following interface
  configuration:

  auto ens9
  iface ens9 inet manual
  bond-master bond0
  bond-primary ens9

  auto ens9.200
  iface ens9.200 inet static
  address 192.168.192.1/28
  vlan-raw-device ens9

  auto ens10
  iface ens10 inet manual
  bond-master bond0

  auto bond0
  iface bond0 inet static
  address 192.168.13.2/24
  bond-mode active-backup
  bond_arp_ip_target 192.168.13.4
  bond_arp_interval 200
  bond-slaves none

  With this configuration, execute the following commands:

      ifup ens9.200
      ifup bond0
      ifdown ens9.200 bond0

  The last command will cause ifdown to forget to unlock the ens9
  interface, then invoke ifenslave's script to bring down the bond
  interface's physical components, which will spawn a second "ifdown
  ens9" which will wait forever for its parent to drop the leaked lock.

  Thanks in advance for your time, and keep up the great work!

  Best regards,
  Peter

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: ifupdown 0.7.47.2ubuntu4.4
  ProcVersionSignature: User Name 3.13.0-133.182-generic 3.13.11-ckt39
  Uname: Linux 3.13.0-133-generic x86_64
  ApportVersion: 2.14.1-0ubuntu3.25
  Architecture: amd64
  Date: Wed Oct 18 09:45:27 2017
  ProcEnviron:
   TERM=screen
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: ifupdown
  UpgradeStatus: No upgrade log present (probably fresh install)

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