Forwarding this bug from Ubuntu reporter Merelin:
http://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/742425

[Problem]
GPU lockup (IPEHR: 0xf9b7b7b7) prior to gdm greeter

[Original Description]
The system hangs before the gdm greeter due to a GPU lockup (*ERROR* Hangcheck timer elapsed... GPU hung).

/var/log/gdm/:0.log:
(EE) intel(0): Detected a hung GPU, disabling acceleration.

/var/log/kern.log:
Mar 25 15:16:01 localhost kernel: [   41.860009] [drm:i915_hangcheck_elapsed] *ERROR* Hangcheck timer elapsed... GPU hung
Mar 25 15:16:01 localhost kernel: [   41.862085] [drm:i915_do_wait_request] *ERROR* i915_do_wait_request returns -11 (awaiting 372 at 345, next 390)
Mar 25 15:16:01 localhost kernel: [   41.862185] [drm:init_ring_common] *ERROR* render ring initialization failed ctl 00000000 head 00000000 tail 00000000 start 00000000
Mar 25 15:16:01 localhost kernel: [   42.005338] [drm:i915_do_wait_request] *ERROR* something (likely vbetool) disabled interrupts, re-enabling
Mar 25 15:16:01 localhost kernel: [   42.025341] [drm:i915_do_wait_request] *ERROR* something (likely vbetool) disabled interrupts, re-enabling
Mar 25 15:16:01 localhost kernel: [   42.045321] [drm:i915_do_wait_request] *ERROR* something (likely vbetool) disabled interrupts, re-enabling

Description:	Ubuntu Natty (development branch)
Release:	11.04

xserver-xorg-video-intel:
  Installed: 2:2.14.0-4ubuntu4
  Candidate: 2:2.14.0-4ubuntu4
  Version table:
 *** 2:2.14.0-4ubuntu4 0
        500 http://archive.ubuntu.com/ubuntu/ natty/main amd64 Packages
        100 /var/lib/dpkg/status

ProblemType: Crash
DistroRelease: Ubuntu 11.04
Package: xserver-xorg-video-intel 2:2.14.0-4ubuntu4
ProcVersionSignature: Ubuntu 2.6.38-7.38-generic 2.6.38
Uname: Linux 2.6.38-7-generic x86_64
Architecture: amd64
Chipset: i946gz
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CompositorRunning: None
DRM.card0.VGA.1:
 status: connected
 enabled: enabled
 dpms: On
 modes: 1440x900 1280x1024 1280x1024 1280x1024 1440x900 1152x864 1024x768 1024x768 1024x768 832x624 800x600 800x600 800x600 800x600 640x480 640x480 640x480 720x400
 edid-base64: AP///////wAwriBpAQEBAQsRAQNsKBl4KtOQollKliQUUFSv7wBxT4GAgYqVAJUPAQEBAQEBmimg0FGEIjBQmDYAmP8QAAAcAAAA/wBWMUQyNjE2CiAgICAgAAAA/QAySx5QDgAKICAgICAgAAAA/ABMMTkyIFdpZGUKICAgADQ=
Date: Fri Mar 18 14:14:43 2011
DistUpgraded: Log time: 2009-03-03 10:04:20.805534
DistroCodename: natty
DistroVariant: ubuntu
DkmsStatus: vboxhost, 4.0.4, 2.6.38-7-generic, x86_64: installed
DumpSignature: (ESR: 0x00000001 IPEHR: 0xf7ffffdf)
ExecutablePath: /usr/share/apport/apport-gpu-error-intel.py
GraphicsCard:
 Intel Corporation 82946GZ/GL Integrated Graphics Controller [8086:2972] (rev 02) (prog-if 00 [VGA controller])
   Subsystem: Lenovo Device [17aa:300b]
MachineType: LENOVO 9645Y8E
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-2.6.38-7-generic root=UUID=2c3d749d-3eae-4db4-8841-84d96773306f ro single
Renderer: Unknown
SourcePackage: xserver-xorg-video-intel
UpgradeStatus: Upgraded to natty on 2009-03-03 (752 days ago)
dmi.bios.date: 04/17/2007
dmi.bios.vendor: LENOVO
dmi.bios.version: 2QKT20AUS
dmi.board.name: LENOVO
dmi.board.vendor: LENOVO
dmi.chassis.asset.tag: 
dmi.chassis.type: 6
dmi.chassis.vendor: LENOVO
dmi.modalias: dmi:bvnLENOVO:bvr2QKT20AUS:bd04/17/2007:svnLENOVO:pn9645Y8E:pvrThinkCentreM55e:rvnLENOVO:rnLENOVO:rvr:cvnLENOVO:ct6:cvr:
dmi.product.name: 9645Y8E
dmi.product.version: ThinkCentre M55e
dmi.sys.vendor: LENOVO
version.compiz: compiz 1:0.9.4git20110322-0ubuntu5
version.libdrm2: libdrm2 2.4.23-1ubuntu5
version.libgl1-mesa-glx: libgl1-mesa-glx 7.10.1-0ubuntu3
version.xserver-xorg: xserver-xorg 1:7.6~3ubuntu11
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:6.14.0-0ubuntu4
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.14.0-4ubuntu4
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:0.0.16+git20110107+b795ca6e-0ubuntu6