Comment # 3 on bug 76558 from Fabio Pedretti

Created attachment 99497 [details]
dmesg after the lockup with kernel 3.13.0-24.47, got switching to a VT

Here is an updated dmesg with kernel 3.13.9 (ubuntu 3.13.0-24.47), only
relevant difference is "on ring 0" is added to this line:
[11757.716140] radeon 0000:01:00.0: GPU lockup (waiting for 0x000000000003dd41
last fence id 0x000000000003dd40 on ring 0)