[Bug 1060249] Re: frontend crashed with signal 5 in free_pending_nulls()

[James Hunt]

The problem with debconf needs a little explanation. As show, the
command that caused the failure was:

/usr/bin/perl -w /usr/share/debconf/frontend /var/lib/dpkg/info/man-
db.postinst triggered /usr/share/man

The 'frontend' perl script determines which type of debconf frontend to
display. In this case, the gnome frontend was selected. debconf then
goes to some pains to ensure that the gtk bindings work. However,
because of the gsettings schema problem, as soon as any perl script
called 'use Gtk2;', the schema was queried, which resulted in the crash.

Since the master debconf process calls 'use Gtk2;' unconditionally, the
schema problem caused debconf (technically the perl interpreter) to
crash.  And since debconf re-execs the original caller (in this case
'/var/lib/dpkg/info/man-db.postinst') as itself, this stopped debconf
from falling back to other frontends as it should as it was now
effectively dead.

The fix is for debconf to only 'use Gtk2;' when it has proven that this
operation can be performed without impacting the perl interpreter. This
allows it to fall back gracefully to alternative frontends.

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https://bugs.launchpad.net/bugs/1060249

Title:
  frontend crashed with signal 5 in free_pending_nulls()

Status in “debconf” package in Ubuntu:
  Confirmed
Status in “gsettings-desktop-schemas” package in Ubuntu:
  Fix Released
Status in “debconf” source package in Precise:
  Invalid
Status in “debconf” source package in Quantal:
  Won't Fix
Status in “gsettings-desktop-schemas” source package in Quantal:
  Fix Released

Bug description:
  Crashed during upgrade from Precise to Quantal without any visible
  effect

  TEST CASE 1:
  1. Install Precise 12.04.1
  2. Upgrade to Quantal

  TEST CASE 2:
  This test case is used to reproduce the debconf crash:
  1. Install Precise 12.04.1 and apply updates
  2. Enable apt repository for Quantal
  3. Install gsettings-desktop-schemas from Quantal:
      $ sudo apt-get install  gsettings-desktop-schemas/quantal
  4. Run man-db trigger manually with:
    $ sudo DEBIAN_FRONTEND=gnome \
          /usr/bin/perl -w /usr/share/debconf/frontend \
          /var/lib/dpkg/info/man-db.postinst triggered \
          /usr/share/man

  => Verify that debconf crashes
  Actually any gtk based application will crash.

  ACTUAL RESULT
  This crash is reported on first login after upgrade.

  
  ProblemType: Crash
  DistroRelease: Ubuntu 12.10
  Package: debconf 1.5.46ubuntu1
  ProcVersionSignature: Ubuntu 3.5.0-16.25-generic 3.5.4
  Uname: Linux 3.5.0-16-generic x86_64
  ApportVersion: 2.6.1-0ubuntu1
  Architecture: amd64
  Date: Tue Oct  2 14:59:09 2012
  ExecutablePath: /usr/share/debconf/frontend
  InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
  InterpreterPath: /usr/bin/perl
  PackageArchitecture: all
  ProcCmdline: /usr/bin/perl -w /usr/share/debconf/frontend /var/lib/dpkg/info/man-db.postinst triggered /usr/share/man
  ProcEnviron:
   TERM=xterm
   PATH=(custom, user)
   LANG=fr_FR.UTF-8
   SHELL=/bin/bash
  Signal: 5
  SourcePackage: debconf
  StacktraceTop:
   ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
   g_node_copy_deep () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
   ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
   ?? ()
   g_signal_emit_valist () from /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
  Title: frontend crashed with signal 5 in g_node_copy_deep()
  UpgradeStatus: Upgraded to quantal on 2012-10-02 (0 days ago)
  UserGroups:

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