xorg 7.4 freezes completely at random times under high cpu load
I'm having sporadic X freezes on my workstation, a quad-core amd64 system running Ubuntu Karmic. At random times, the X server will freeze completely ; neither the mouse nor the keyboard respond to anything. However, I can ssh into the machine, and all of the processes on the system seem to be working fine. I tried restarting gdm, and even though gdm claims to have restarted, the screen remains frozen, with no response to mouse or keyboard. The [Xorg] process as reported by 'ps auwx' is blocking (in the "D" state) and does not respond to kill -15 or kill -9.
This has been happening ever since I got this machine about a month ago. It's been quite difficult to figure out what causes it, since it happens sporadically (maybe once or twice a week). So far, it looks like the freezes tend to correlate with high CPU load on the machine, and sometimes it seems to happen when I am doing something that involves fancy compiz effects on my desktop (but not always).
I am using an nVidia GTS 250 video card with the stock Ubuntu nVidia drivers (version 185.18.36). I've attached the output from nvidia-bug-report.sh, although it froze collecting the report and I had to kill it. When a freeze happened this morning, I noticed that the system log had a traceback in it, so I hope that's going to be helpful.
I'd love to get some feedback from this, since this greatly interrupts my work, and it's just sort of frustrating in general. Please let me know if I need to provide any additional information. Thanks !