Created attachment 1204602 [details]
Kernel trace after gpu hand

Description of problem:

The computer would frequently hang when left alone (most probably while the screen is locked by gdm).

The mouse cursor would still show and move, but on a blank screen.
Any other command (keyboard, TTY) are irresponsive and there is no other choice than rebooting.

How reproducible:

It happens often but cannot be reproduced on purpose.

Actual results:

The computer hangs with the mouse cursor on a blank screen.

Expected results:

The lockout gdm screen should show up.

Additional info:

Attached kernel trace shows a lot of error traces.