https://bugs.freedesktop.org/show_bug.cgi?id=84500
--- Comment #39 from drago01@gmail.com --- 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).