After updating the kernel to 2.6.32-220.2.1 this morning and restarting, the system locked up completely after a few minutes browsing the web and I had to do a hard reset. /var/log/messages shows the following:
Dec 28 10:28:36 KCHV5GC kernel: [drm:i915_hangcheck_elapsed] *ERROR* Hangcheck timer elapsed... GPU hung Dec 28 10:28:36 KCHV5GC kernel: [drm] capturing error event; look for more information in /debug/dri/0/i915_error_state Dec 28 10:28:36 KCHV5GC kernel: [drm:i915_gem_wait_request] *ERROR* i915_gem_wait_request returns -11 (awaiting 115356 at 115242, next 115359) Reverting to the 2.6.32-131.21.1 kernel solved the problem for now. I'm using an old IBM Thinkcentre S50 with a Pentium 4 processor and 82865G graphics.
