Forwarding this bug from Ubuntu reporter sergi sergi:
http://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/979446

[Problem]
GPU lockup with recovery, followed by a WARNING in intel_enable_pipe.

[ 2537.684132] [drm:i915_hangcheck_elapsed] *ERROR* Hangcheck timer elapsed... GPU hung
[ 2537.684147] [drm] capturing error event; look for more information in /debug/dri/0/i915_error_state
[ 2537.685618] [drm:i915_wait_request] *ERROR* i915_wait_request returns -11 (awaiting 161236 at 161230, next 161241)
[ 2537.685998] [drm:init_ring_common] *ERROR* render ring initialization failed ctl 00000000 head 00000000 tail 00000000 start 00000000
[ 2537.748362] [drm] Changing LVDS panel from (+hsync, +vsync) to (-hsync, -vsync)
[ 2537.748517] ------------[ cut here ]------------
[ 2537.748546] WARNING: at /build/buildd/linux-3.2.0/drivers/gpu/drm/i915/intel_display.c:793 intel_enable_pipe+0x144/0x150 [i915]()
[ 2537.748550] Hardware name: 7661AQ1
[ 2537.748552] PLL state assertion failure (expected on, current off)
[ 2537.748554] Modules linked in: joydev parport_pc ppdev rfcomm bnep bluetooth snd_hda_codec_analog pcmcia psmouse serio_raw yenta_socket pcmcia_rsrc pcmcia_core arc4 i915 snd_hda_intel snd_hda_codec snd_hwdep snd_pcm snd_seq_midi snd_rawmidi snd_seq_midi_event snd_seq thinkpad_acpi nvram tpm_tis iwl3945 iwl_legacy snd_timer mac80211 snd_seq_device drm_kms_helper cfg80211 wmi mac_hid snd drm i2c_algo_bit video soundcore snd_page_alloc lp parport firewire_ohci firewire_core crc_itu_t e1000e
[ 2537.748603] Pid: 57, comm: kworker/u:6 Not tainted 3.2.0-23-generic-pae #36-Ubuntu
[ 2537.748606] Call Trace:
[ 2537.748614]  [<c105a512>] warn_slowpath_common+0x72/0xa0
[ 2537.748631]  [<f89b7834>] ? intel_enable_pipe+0x144/0x150 [i915]
[ 2537.748646]  [<f89b7834>] ? intel_enable_pipe+0x144/0x150 [i915]
[ 2537.748651]  [<c105a5e3>] warn_slowpath_fmt+0x33/0x40
[ 2537.748666]  [<f89b7834>] intel_enable_pipe+0x144/0x150 [i915]
[ 2537.748683]  [<f89baa78>] i9xx_crtc_mode_set+0x688/0xc60 [i915]
[ 2537.748698]  [<f86486fc>] ? vblank_disable_and_save+0x16c/0x190 [drm]
[ 2537.748713]  [<f89b0d19>] ? i965_update_wm+0x189/0x220 [i915]
[ 2537.748729]  [<f89b43ac>] intel_crtc_mode_set+0x5c/0x90 [i915]
[ 2537.748737]  [<f8603b72>] drm_crtc_helper_set_mode+0x2a2/0x470 [drm_kms_helper]
[ 2537.748746]  [<f8603dad>] drm_helper_resume_force_mode+0x6d/0x140 [drm_kms_helper]
[ 2537.748759]  [<f8996231>] i915_reset+0x211/0x2d0 [i915]
[ 2537.748771]  [<f899a68e>] i915_error_work_func+0xae/0xf0 [i915]
[ 2537.748778]  [<c1074c81>] process_one_work+0x101/0x3a0
[ 2537.748783]  [<c15af6b0>] ? common_interrupt+0x30/0x38
[ 2537.748795]  [<f899a5e0>] ? i915_driver_irq_postinstall+0x170/0x170 [i915]
[ 2537.748799]  [<c1075744>] worker_thread+0x124/0x2d0
[ 2537.748803]  [<c1075620>] ? manage_workers.isra.27+0x110/0x110
[ 2537.748807]  [<c107956d>] kthread+0x6d/0x80
[ 2537.748811]  [<c1079500>] ? flush_kthread_worker+0x80/0x80
[ 2537.748815]  [<c15af6be>] kernel_thread_helper+0x6/0x10
[ 2537.748817] ---[ end trace 8f54fda12e5f6d12 ]---
[ 2537.860046] ------------[ cut here ]------------

[Original Description]
no idea what happends

ProblemType: Crash
DistroRelease: Ubuntu 12.04
Package: xserver-xorg-video-intel 2:2.17.0-1ubuntu4
ProcVersionSignature: Ubuntu 3.2.0-23.36-generic-pae 3.2.14
Uname: Linux 3.2.0-23-generic-pae i686
.tmp.unity.support.test.0:
 
ApportVersion: 2.0.1-0ubuntu1
Architecture: i386
Chipset: i965gm
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CompositorRunning: compiz
Date: Wed Apr 11 23:38:23 2012
DistUpgraded: Fresh install
DistroCodename: precise
DistroVariant: ubuntu
DuplicateSignature: [i965gm] GPU lockup  render.IPEHR: 0x60020100 Ubuntu 12.04
ExecutablePath: /usr/share/apport/apport-gpu-error-intel.py
GraphicsCard:
 Intel Corporation Mobile GM965/GL960 Integrated Graphics Controller (primary) [8086:2a02] (rev 0c) (prog-if 00 [VGA controller])
   Subsystem: Lenovo T61 [17aa:20b5]
   Subsystem: Lenovo T61 [17aa:20b5]
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Alpha i386 (20120218)
InterpreterPath: /usr/bin/python2.7
MachineType: LENOVO 7661AQ1
PccardctlIdent:
 Socket 0:
   no product info available
PccardctlStatus:
 Socket 0:
   no card
ProcCmdline: /usr/bin/python /usr/share/apport/apport-gpu-error-intel.py
ProcEnviron:
 
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.2.0-23-generic-pae root=UUID=9a979010-b4c9-4882-a591-941c35c30a64 ro quiet splash vt.handoff=7
RelatedPackageVersions:
 xserver-xorg             1:7.6+12ubuntu1
 libdrm2                  2.4.32-1ubuntu1
 xserver-xorg-video-intel 2:2.17.0-1ubuntu4
SourcePackage: xserver-xorg-video-intel
Title: [i965gm] False GPU lockup  render.IPEHR: 0x60020100
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups:
 
dmi.bios.date: 03/18/2011
dmi.bios.vendor: LENOVO
dmi.bios.version: 7LETC9WW (2.29 )
dmi.board.name: 7661AQ1
dmi.board.vendor: LENOVO
dmi.board.version: Not Available
dmi.chassis.asset.tag: 100014114681
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: Not Available
dmi.modalias: dmi:bvnLENOVO:bvr7LETC9WW(2.29):bd03/18/2011:svnLENOVO:pn7661AQ1:pvrThinkPadT61:rvnLENOVO:rn7661AQ1:rvrNotAvailable:cvnLENOVO:ct10:cvrNotAvailable:
dmi.product.name: 7661AQ1
dmi.product.version: ThinkPad T61
dmi.sys.vendor: LENOVO
version.compiz: compiz 1:0.9.7.4-0ubuntu3
version.libdrm2: libdrm2 2.4.32-1ubuntu1
version.libgl1-mesa-dri: libgl1-mesa-dri 8.0.2-0ubuntu3
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 8.0.2-0ubuntu3
version.xserver-xorg-core: xserver-xorg-core 2:1.11.4-0ubuntu10
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.7.0-0ubuntu1
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:6.14.99~git20111219.aacbd629-0ubuntu2
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.17.0-1ubuntu4
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:0.0.16+git20111201+b5534a1-1build2