Xorg crashed with signal 7 in start_thread()

[Alexandr Novel]

Tried to use gdb to catch it, however the virtual ttys are blacked out, not frozen, thus could not do anything with it.
If someone can give me a practical advice on how to back-trace Xorg, I could help to troubleshoot it.

ProblemType: Crash
DistroRelease: Ubuntu 14.04
Package: xserver-xorg-core 2:1.15.1-0ubuntu2.1
ProcVersionSignature: Ubuntu 3.5.0-18.29-generic 3.5.7
Uname: Linux 3.5.0-18-generic x86_64
.tmp.unity.support.test.0:

ApportVersion: 2.14.1-0ubuntu3.5
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CompositorRunning: compiz
CompositorUnredirectDriverBlacklist: '(nouveau|Intel).*Mesa 8.0'
CompositorUnredirectFSW: true
CrashCounter: 1
Date: Mon Oct 20 12:28:56 2014
DistUpgraded: 2014-08-19 14:00:57,964 DEBUG enabling apt cron job
DistroCodename: trusty
DistroVariant: ubuntu
ExecutablePath: /usr/bin/Xorg
ExtraDebuggingInterest: Yes
GraphicsCard:
 Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller [8086:2a42] (rev 07) (prog-if 00 [VGA controller])
   Subsystem: Lenovo Device [17aa:20e4]
   Subsystem: Lenovo Device [17aa:20e4]
InstallationDate: Installed on 2012-06-22 (850 days ago)
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
MachineType: LENOVO 647341U
PccardctlIdent:
 Socket 0:
   no product info available
PccardctlStatus:
 Socket 0:
   no card
ProcCmdline: /usr/bin/X -core :0 -seat seat0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch
ProcEnviron:

ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.5.0-18-generic root=UUID=cc4e5011-50ff-4db4-856e-d1ef85ab4327 ro crashkernel=384M-:128M
Signal: 7
SourcePackage: xorg-server
StacktraceTop:
 ?? () from /usr/lib/xorg/modules/drivers/intel_drv.so
 ?? () from /usr/lib/xorg/modules/drivers/intel_drv.so
 ?? () from /usr/lib/xorg/modules/drivers/intel_drv.so
 ?? () from /usr/lib/xorg/modules/drivers/intel_drv.so
 start_thread (arg=0x7f5a1f2ac700) at pthread_create.c:312
Title: Xorg crashed with signal 7 in start_thread()
UpgradeStatus: Upgraded to trusty on 2014-08-19 (61 days ago)
UserGroups:

dmi.bios.date: 10/10/2012
dmi.bios.vendor: LENOVO
dmi.bios.version: 7VET95WW (3.25 )
dmi.board.name: 647341U
dmi.board.vendor: LENOVO
dmi.board.version: Not Available
dmi.chassis.asset.tag: No Asset Information
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: Not Available
dmi.modalias: dmi:bvnLENOVO:bvr7VET95WW(3.25):bd10/10/2012:svnLENOVO:pn647341U:pvrThinkPadT400:rvnLENOVO:rn647341U:rvrNotAvailable:cvnLENOVO:ct10:cvrNotAvailable:
dmi.product.name: 647341U
dmi.product.version: ThinkPad T400
dmi.sys.vendor: LENOVO
version.compiz: compiz 1:0.9.11.2+14.04.20140714-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.52-1
version.libgl1-mesa-dri: libgl1-mesa-dri 10.1.3-0ubuntu0.2
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 10.1.3-0ubuntu0.2
version.xserver-xorg-core: xserver-xorg-core 2:1.15.1-0ubuntu2.1
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.8.2-1ubuntu2
version.xserver-xorg-video-ati: xserver-xorg-video-ati N/A
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.910-0ubuntu1.1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau N/A
xserver.bootTime: Mon Oct 20 12:29:04 2014
xserver.configfile: default
xserver.errors:

xserver.logfile: /var/log/Xorg.0.log
xserver.outputs:
 product id 16437
 vendor LEN
xserver.version: 2:1.15.1-0ubuntu2.1

[Apport retracing service (apport)]

StacktraceTop:
 _tor_blt_src (in=0x7fff0d3d6bd0, box=<optimized out>, v=16 '\020') at ../../../src/sna/sna_trapezoids_imprecise.c:2197
 tor_blt (unbounded=1, height=<optimized out>, y=<optimized out>, span=0x7f5a1fb67350 <tor_blt_src>, clip=0x7f5a278e79e0, op=0x7fff0d3d6bd0, converter=0x7f5a1f2aa300, sna=0x0) at ../../../src/sna/sna_trapezoids_imprecise.c:1127
 tor_render (sna=sna@entry=0x0, converter=converter@entry=0x7f5a1f2aa300, op=op@entry=0x7fff0d3d6bd0, clip=0x7f5a278e79e0, span=0x7f5a1fb67350 <tor_blt_src>, unbounded=1) at ../../../src/sna/sna_trapezoids_imprecise.c:1230
 inplace_thread (arg=0x7fff0d3d6bb8) at ../../../src/sna/sna_trapezoids_imprecise.c:2898
 __run__ (arg=0x7f5a269fe0e0) at ../../../src/sna/sna_threads.c:65

[Alexandr Novel (normalex)]

The succesfull workaround for Xorg crashing on Intel GM45 integrated graphics on Lenovo T400 was to create the the following file

/usr/share/X11/xorg.conf.d/20-intel-gm45.conf

Section "Device"
    Identifier "Intel Graphics"
    Driver "intel"
    Option "AccelMethod" "uxa"
EndSection

Swtiching from SNA to UXA alleviated all the problems.

As a side note, gtkperf tool is very reliable to reproduce SNA Xorg crashes.