sorry, I could neither find the place where to report this bug, nor understand whether to report this bug at all. Therefore I ask it here:
Since I received my X220 three month ago I use ubuntu 11.04 with gnome. Up to a few times per week I get an xorg freeze (checked the (non-)symptoms here https://wiki.ubuntu.com/X/Troubleshooting/Freeze). Answering the important questions on the same site: Nothing particular to report, except that I was using firefox and one or more terminal windows.
When ssh into the frozen computer, it shows a GPU hung. The output of dmesg:
... [ 4241.536364] [drm:i915_hangcheck_elapsed] *ERROR* Hangcheck timer elapsed... GPU hung [ 4241.547571] [drm:i915_do_wait_request] *ERROR* i915_do_wait_request returns -11 (awaiting 911303 at 911300, next 911304) [ 4241.917038] show_signal_msg: 15 callbacks suppressed [ 4241.917042] compiz: segfault at 0 ip 00007f63c39adbe8 sp 00007fffa403f9f0 error 6 in i965_dri.so[7f63c393c000+ac000] [ 4243.616957] compiz: segfault at 0 ip 00007f9d9ca17be8 sp 00007fff41979e80 error 6 in i965_dri.so[7f9d9c9a6000+ac000] ...
... [ 4251.051] (EE) intel(0): Detected a hung GPU, disabling acceleration. [ 4251.052] (WW) intel(0): intel_uxa_prepare_access: bo map failed: Input/output error [ 4251.052] (WW) intel(0): intel_uxa_prepare_access: bo map failed: Input/output error ...
I think I will just disable compiz, but I wanted to make sure that this problem is known and maybe there is already a simple solution for it.