"gnome-control-center display" crashes if no RANDR extension

[Stéphane Gourichon]

The problem can be reproduced at will by clicking on display settings icon, but also by typing this :

gnome-control-center display

A window appears, complains "Could not get screen information" "RANDR extension is not present".

$ LC_ALL=C gnome-control-center display

(gnome-control-center:13078): Gtk-WARNING **: GtkTable does not have a property called expand

(gnome-control-center:13078): Gtk-WARNING **: GtkTable does not have a property called fill

(gnome-control-center:13078): Gtk-WARNING **: GtkTable does not have a property called position

(gnome-control-center:13078): GLib-GObject-WARNING **: invalid (NULL) pointer instance

(gnome-control-center:13078): GLib-GObject-CRITICAL **: g_signal_connect_data: assertion `G_TYPE_CHECK_INSTANCE (instance)' failed
Erreur de segmentation (core dumped)

ProblemType: Crash
DistroRelease: Ubuntu 12.04
Package: gnome-control-center 1:3.4.0-0ubuntu6
ProcVersionSignature: Ubuntu 3.2.0-23.36-generic 3.2.14
Uname: Linux 3.2.0-23-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.0.1-0ubuntu2
Architecture: amd64
Date: Thu Apr 12 16:41:38 2012
ExecutablePath: /usr/bin/gnome-control-center
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Beta amd64 (20120410)
ProcCmdline: gnome-control-center --overview
ProcEnviron:
 PATH=(custom, user)
 LANG=fr_FR.UTF-8
 SHELL=/bin/bash
SegvAnalysis:
 Segfault happened at: 0x7fb28dcb7c07 <gtk_widget_size_allocate+23>: mov 0x18(%rdi),%rbp
 PC (0x7fb28dcb7c07) ok
 source "0x18(%rdi)" (0x00000018) not located in a known VMA region (needed readable region)!
 destination "%rbp" ok
SegvReason: reading NULL VMA
Signal: 11
SourcePackage: gnome-control-center
StacktraceTop:
 gtk_widget_size_allocate () from /usr/lib/x86_64-linux-gnu/libgtk-3.so.0
 ?? () from /usr/lib/libgnome-control-center.so.1
 g_cclosure_marshal_VOID__BOXEDv () from /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
 ?? () from /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
 g_signal_emit_valist () from /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0
Title: gnome-control-center crashed with SIGSEGV in gtk_widget_size_allocate()
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
usr_lib_gnome-control-center:
 activity-log-manager-control-center 0.9.4-0ubuntu3
 deja-dup 22.0-0ubuntu2
 gnome-bluetooth 3.2.2-0ubuntu5
 indicator-datetime 0.3.94-0ubuntu1

[Stéphane Gourichon (stephane-gourichon-lpad)]

"No RANDR extension" was the result of clicking "nvidia-settings" (installed automatically by Ubuntu installer) to use external monitor as "separate X screen" with "xinerama", no need to open a terminal to get into this.

[Apport retracing service (apport)]

StacktraceTop:
 gtk_widget_size_allocate (widget=0x0, allocation=0x7fff56391130) at /build/buildd/gtk+3.0-3.4.0/./gtk/gtkwidget.c:4872
 ?? () from /tmp/tmpLg5uJs/usr/lib/libgnome-control-center.so.1
 g_cclosure_marshal_VOID__BOXEDv (closure=0x7fb2903e1d30, return_value=<optimized out>, instance=0x7fb290845120, args=<optimized out>, marshal_data=<optimized out>, n_params=<optimized out>, param_types=0x7fb2903e1da0) at /build/buildd/glib2.0-2.32.0/./gobject/gmarshal.c:1160
 _g_closure_invoke_va (closure=0x7fb2903e1d30, return_value=0x0, instance=0x7fb290845120, args=0x7fff56391468, n_params=1, param_types=<optimized out>) at /build/buildd/glib2.0-2.32.0/./gobject/gclosure.c:840
 g_signal_emit_valist (instance=0x7fb290845120, signal_id=<optimized out>, detail=0, var_args=<optimized out>) at /build/buildd/glib2.0-2.32.0/./gobject/gsignal.c:3207

[TJ (tj)]

The message "RANDR extension is not present" originates from the package "gnome-desktop3"

libgnome-desktop/gnome-rr.c::gnome_rr_screen_initable_init()

if (XRRQueryExtension (dpy, &event_base, &ignore))
{
...
}
else
{
   g_set_error (error, GNOME_RR_ERROR, GNOME_RR_ERROR_NO_RANDR_EXTENSION,
                   _("RANDR extension is not present"));

  return false;
}

[TJ (tj)]

libgnome-desktop/gnome-rr.c::gnome_rr_screen_new() says:

 * Returns: a unique #GnomeRRScreen instance, specific to the @screen, or NULL
 * if this could not be created, for instance if the driver does not support
 * Xrandr 1.2. Each #GdkScreen thus has a single instance of #GnomeRRScreen.

therefore in gnome-control-center panels/display/cc-diaply-panel.c::cc_display_panel_constructor() the following code is incorrect:

  self->priv->screen = gnome_rr_screen_new (gdk_screen_get_default (), &error);
  g_signal_connect (self->priv->screen, "changed", G_CALLBACK (on_screen_changed), self);
  if (!self->priv->screen)
    {
      error_message (NULL, _("Could not get screen information"), error->message);
      g_error_free (error);

if the call to gnome_rr_screen_new() returns NULL, as it will if no RANDR is available, the subsequent setup of the signal:

g_signal_connect (self->priv->screen, "changed", G_CALLBACK (on_screen_changed), self);

is done with self->priv->screen == NULL

So when that signal fires it passes a NULL screen pointer to on_screen_changed(). Passing the NULL pointer doesn't matter since it isn't used in the call-back, but self->priv->screen is used:

on_screen_changed (GnomeRRScreen *scr,
                   gpointer data)
{
  GnomeRRConfig *current;
  CcDisplayPanel *self = data;

  current = gnome_rr_config_new_current (self->priv->screen, NULL);
  gnome_rr_config_ensure_primary (current);

So current will be NULL after calling gnome_rr_config_new_current()

[TJ (tj)]

I've uploaded the potential fix to my PPA for Precise. Please test and report back.

https://launchpad.net/~tj/+archive/bugfixes

[Sebastien Bacher (seb128)]

The bug hasn't seen any activity in years and there has been no recent similar reports, the code also changed quite a lot since and it's likely the issue doesn't exist anymore. Closing, feel free to open a new report if you still get problems in recent Ubuntu versions

[Stéphane Gourichon (stephane-gourichon-lpad)]

Makes sense. Besides, I've been using XFCE for a long time now, so have not had any visibility whether this bug still occurs with Gnome.