Forwarding this bug from a Ubuntu reporter:
https://bugs.edge.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/282081

[Problem]
X hangs on return from any screensaver, with Xorg at 100% and a moving cursor over an empty background.  Killing and restarting X results in same condition.

[Steps to Reproduce]
recreate 1:
--------------
 - configure a screen saver (blank, 3D, OpenGL, whatever...)
 - let the computer idle for a few hours
 - when returning from the screensaver, Xorg sits at 100% CPU and yields a moving cursor over empty background. No windows, no menu etc. Keyboard not responsive either (no ctl-alt-backspace, no ctl-alt-F1...)
 - killing X takes you to "recreate 2"

recreate 2:
--------------
 - log in under GDM (enter a gnome session)
 - log out
 - log in again => X starts spinning at 100% and yields a moving cursor over empty background. No windows, no menu etc. Keyboard not responsive either (no ctl-alt-backspace, no ctl-alt-F1...)

In either case, the only option is to reboot the computer.

I have the _impression_ that using a GL screensaver (such as hypetorus) accelerates the recreate 1 procedure. In this scenario, hypertorus would sit at 100% CPU. Killing it would yield an Xorg at 100% CPU, and then continue from step 3 of recreate 1.


[Original Report]
System: Ubuntu Intrepid Ibex (beta) 8.10 up to date as of 11 Oct 2008.

Linuxroot@fdetienn-desktop:~# uname -a
 fdetienn-desktop 2.6.27-7-generic #1 SMP Fri Oct 10 03:55:24 UTC 2008 i686 GNU/Linux

root@fdetienn-desktop:~# lsb_release -rd
Description: Ubuntu intrepid (development branch)
Release: 8.10

This is going to be a messy report as I see things but do not know in which order they happen or even if they are truly related. They are correlated though.

I am running Ubuntu 8.10 on a Dell Hybrid Studio. 4GB RAM and X3100 Intel accelerators.

When leaving X running for some time (undetermined yet) with an OpenGL screensaver (Hypertorus in this case), the system display finally hangs and I can not return to session (not even a password prompt). The screen remains black and backlit.

SSH still works and I see Hypertorus spinning at 100% CPU.

If I kill Hypertorus and gnome-screensaver, the screen flashes once but nothing better happens. I then see Xorg at 100% CPU.

If I kill X, gdm restarts it and I get a user prompt. After typing my username/password, X wipes the screen and I see an orange background but then X goes back spinning at 100% CPU. This takes me to the previous point. There is never a way to get a working X display.

The VT consoles are also broken; they remain with corrupted leftovers of the X display (I see part of the orange background and the mouse pointer + some colorful areas).

The only outstanding message is:

[42627.033483] mtrr: type mismatch for d0000000,10000000 old: write-back new: write-combining
[42772.634036] mtrr: type mismatch for d0000000,10000000 old: write-back new: write-combining
[42810.157626] mtrr: type mismatch for d0000000,10000000 old: write-back new: write-combining

from kernel.log (also visible in dmesg).

 - opengl is not guilty - had a GL screensaver (hypertorus) running for hours
 - the MTRR error does NOT seem to be the root cause of the problem; I systematically get an MTRR at boot

It seems ACPI is the issue:
   - causes the above symptoms (X hang at 100% CPU; not recoverable) after restore from screen power saving
   - ACPI sometimes causes hang at boots
   - hang at resume after suspend

the same situation happens even without screen blanking.

I just need to let the computer run for a few hours (seemingly random time) for the problem to happen.

The visible symptoms are:
 - no windows are visible; no gnome menus, dockbar -- just an empty background (orange)
 - mouse pointer still moves
 - keyboard dead (ctl-alt-backspace does not work)

SSH'ing to the computer shows Xorg at 100% CPU. This is the moment I took the logs above.

Killing Xorg takes me back to the gdm greeter but Xorg immediately goes back to 100% CPU when I log in again.

[lspci]
00:00.0 Host bridge [0600]: Intel Corporation Mobile PM965/GM965/GL960 Memory Controller Hub [8086:2a00] (rev 03)
	Subsystem: Dell Device [1028:0279]

00:02.0 VGA compatible controller [0300]: Intel Corporation Mobile GM965/GL960 Integrated Graphics Controller [8086:2a02] (rev 03)
	Subsystem: Dell Device [1028:0279]