GTK+2.19.0
DirectFB 1.4.2

I found that the system will crash in "find_native_sibling_above" gdk/gdkwindow.c  traced by gdb, the parameter parent will be NULL.

I add the debug message, the output is:

(gtk-demo:294): Gdk-WARNING **: find_native_sibling_above_helper: child
(gtk-demo:294): Gdk-WARNING **: find_native_sibling_above_helper: for
(gtk-demo:294): Gdk-WARNING **: find_native_sibling_above: parent==null


the code is:

static GdkWindowObject *
find_native_sibling_above_helper (GdkWindowObject *parent,
                                  GdkWindowObject *child)
{
  GdkWindowObject *w;
  GList *l;

  //for debug, 4 lines 
  if (!parent) {
    g_warning ("find_native_sibling_above_helper: parent==null");
    return NULL;
  }
  if (child)
    {
      //for debug, 1 line
      g_warning ("find_native_sibling_above_helper: child");
      l = g_list_find (parent->children, child);
      g_assert (l != NULL); /* Better be a child of its parent... */
      //for debug, 2 lines
      if (!l)
        g_warning ("find_native_sibling_above_helper: l==null");
      l = l->prev; /* Start looking at the one above the child */
    }
  else
    l = g_list_last (parent->children);
  //for debug, 1 line
  g_warning ("find_native_sibling_above_helper: for");
  for (; l != NULL; l = l->prev)
    {
      w = l->data;
      //for debug, 2 lines
      if(!w)
        g_warning ("find_native_sibling_above_helper: w==null");
      if (gdk_window_has_impl (w))
        return w;

      g_assert (parent != w);
      w = find_native_sibling_above_helper (w, NULL);
      if (w)
        return w;
    }

  return NULL;
}

static GdkWindowObject *
find_native_sibling_above (GdkWindowObject *parent,
                           GdkWindowObject *child)
{
  GdkWindowObject *w;

  //for debug, 4 lines
  if (!parent) {
    g_warning ("find_native_sibling_above: parent==null");
    return NULL;
  }
  w = find_native_sibling_above_helper (parent, child);
  if (w)
    return w;

  if (gdk_window_has_impl (parent))
    return NULL;
  else
    return find_native_sibling_above (parent->parent, parent);
}