https://bugs.freedesktop.org/show_bug.cgi?id=79980
--- Comment #104 from Alex Deucher agd5f@yahoo.com --- (In reply to comment #103)
I just saw this in dmesg: radeon 0000:01:00.0: Packet0 not allowed!
Some userspace component is generating an invalid command stream. Probably a bad packet count somewhere.