Comment # 24 on bug 1018353 from Richard Bos

Backtrace:
drm_modeset_lock_all
drm_fb_helper_restore_fbdev_mode_unlocked
psb_driver_lastclose
drm_lastclose
drm_release
__fput
task_work_run
exit_to_usermode_loop
syscall_return_slowpath
int_ret_from_sys_call

Searching with these functions, it shows this (closed) bug report:
  https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1567781
(no solution)

What is this:
when not blacklisting the gma500_gfx driver via /etc/modprobe.d/blacklist.conf
( is it possible to blacklist a driver )?

Anyway, if you need more info, please let me know.