Comment # 6 on bug 958794 from Takashi Iwai

Yes, you can try downgrade the GM version at any time.  Try to downgrade
suspicious ones (e.g. kernel, X-related ones) to see whether the issue is gone
with that.

BTW, if the machine reboots by itself, I'm afraid that the atomic message is a
red herring.  It might show some problem in graphics, but usually such a
problem won't lead to crash/reboot, but at most GPU hang.

In anyway, at testing the old kernel, don't forget to uninstall the test KMP. 
This may override even the old kernel.