https://bugs.freedesktop.org/show_bug.cgi?id=84500
--- Comment #40 from Alexandre Demers alexandre.f.demers@gmail.com --- (In reply to drago01 from comment #39)
I am seeing those messages too here:
radeon 0000:02:00.0: Packet0 not allowed!
on a R9 270X ... no hangs or anything else just the message in the log (3.17.3 / mesa 10.3.3 on F20).
I haven't hit it for a while. But I'm testing a 3.18 kernel with latest mesa from git. This could be a clue.