X server not responding when querying X pointer position

[Thierry Reding]

Hi,

I see strange behaviour with a program I'm developing. Basically the program
embeds WebKit to display a graphical user-interface. Sometimes during testing
(which is just playing around with some buttons on the screen) it happens that
the GUI gets stuck completely.

Attaching to the program at runtime after reproducing the hang, I was able to
get the following backtrace (paths shortened for readability):

	(gdb) bt
	#0  0xffffe424 in __kernel_vsyscall ()
	#1  0xb5693916 in ?? () from /lib/libc.so.6
	#2  0xb56939aa in poll () from /lib/libc.so.6
	#3  0xb55c2640 in _xcb_conn_wait (c=0x867a748, cond=0xbfe46ec0, vector=0x0, count=0x0)
	    at .../build/packages/xorg/lib/xcb/libxcb-1.7/src/xcb_conn.c:313
	#4  0xb55c3f87 in xcb_wait_for_reply (c=0x867a748, request=6396, e=0xbfe46f5c)
	    at .../build/packages/xorg/lib/xcb/libxcb-1.7/src/xcb_in.c:378
	#5  0xb761b458 in _XReply () from /usr/lib/libX11.so.6
	#6  0xb7610b5e in XQueryPointer () from /usr/lib/libX11.so.6
	#7  0xb5cd610b in _gdk_windowing_window_at_pointer (display=0x86850b0, win_x=0xbfe4713c, win_y=0xbfe47138, mask=0x0, get_toplevel=0)
	    at .../build/packages/libs/gtk/gtk+-2.24.5/gdk/x11/gdkwindow-x11.c:3299
	#8  0xb5c82b9c in gdk_display_real_get_window_at_pointer (display=0x86850b0, win_x=0xbfe4716c, win_y=0xbfe47168)
	    at .../build/packages/libs/gtk/gtk+-2.24.5/gdk/gdkdisplay.c:533
	#9  0xb5c8372f in IA__gdk_display_get_window_at_pointer (display=0x86850b0, win_x=0xbfe4720c, win_y=0xbfe47208)
	    at .../build/packages/libs/gtk/gtk+-2.24.5/gdk/gdkdisplay.c:614
	#10 0xb5f7dd26 in IA__gtk_tooltip_trigger_tooltip_query (display=0x86850b0)
	    at .../build/packages/libs/gtk/gtk+-2.24.5/gtk/gtktooltip.c:467
	#11 0xb632ec5f in webkit_web_view_set_tooltip_text () from /usr/lib/libwebkitgtk-1.0.so.0
	#12 0xb62fc20e in ?? () from /usr/lib/libwebkitgtk-1.0.so.0
	#13 0xb68296a4 in ?? () from /usr/lib/libwebkitgtk-1.0.so.0
	#14 0xb6850206 in ?? () from /usr/lib/libwebkitgtk-1.0.so.0
	#15 0xb6330819 in ?? () from /usr/lib/libwebkitgtk-1.0.so.0
	#16 0xb5e8fd44 in _gtk_marshal_BOOLEAN__BOXED (closure=0x87980e0, return_value=0xbfe475f4, n_param_values=2, param_values=0x87a5cc8, invocation_hint=0xbfe475e0, marshal_data=0xb63307b0)
	    at .../build/packages/libs/gtk/gtk+-2.24.5/gtk/gtkmarshalers.c:86
	#17 0xb59014e7 in ?? () from /usr/lib/libgobject-2.0.so.0
	#18 0xb5902b92 in g_closure_invoke () from /usr/lib/libgobject-2.0.so.0
	#19 0xb5914bc4 in ?? () from /usr/lib/libgobject-2.0.so.0
	#20 0xb591c6a6 in g_signal_emit_valist () from /usr/lib/libgobject-2.0.so.0
	#21 0xb591caa2 in g_signal_emit () from /usr/lib/libgobject-2.0.so.0
	#22 0xb5fc3a56 in gtk_widget_event_internal (widget=0x87bd000, event=0x868b338)
	    at .../build/packages/libs/gtk/gtk+-2.24.5/gtk/gtkwidget.c:4984
	#23 0xb5e8debd in IA__gtk_propagate_event (widget=0x87bd000, event=0x868b338)
	    at .../build/packages/libs/gtk/gtk+-2.24.5/gtk/gtkmain.c:2489
	#24 0xb5e8e2bf in IA__gtk_main_do_event (event=<value optimized out>)
	    at .../build/packages/libs/gtk/gtk+-2.24.5/gtk/gtkmain.c:1684
	#25 0xb5cc21aa in gdk_event_dispatch (source=0x868d858, callback=0, user_data=0x0)
	    at .../build/packages/libs/gtk/gtk+-2.24.5/gdk/x11/gdkevents-x11.c:2377
	#26 0xb581786e in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
	#27 0xb5817f08 in ?? () from /usr/lib/libglib-2.0.so.0
	#28 0xb58185c3 in g_main_loop_run () from /usr/lib/libglib-2.0.so.0
	#29 0x0804ebd6 in main (argc=1, argv=0xbfe47b64)
	    at .../build/packages/net/remote-control/remote-control-0.5.0/bin/remote-control/remote-control.c:374

Looking at this there seems to be a problem when trying to display tooltips,
possibly for one of the buttons being pressed/hovered over. My best guess is
that for some reason, the X server is not responding to the XQueryPointer
request.

I'm running this on X.Org server 1.10.2, with libX11 1.4.3 and libxcb 1.7. I'm
also cross-compiling this from x86_64 to i786 if that is at all important.

Does anybody have any ideas about what might be the cause or do you have any
pointers as to where I should look further? I can provide more information if
needed. Also I wasn't sure whether or not to Cc the XCB mailing list on this
because it seems more of an X server problem. I could be completely wrong of
course.

Cheers,
Thierry
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