First of all, please attach the Xorg.0.log file and the output of glxinfo and
dmesg.

(In reply to comment #6)
> One thing I noticed additionally: I have Radeon DPM enabled, despite my
> Kernel requiring a boot parameter for that as that's not yet default.

Does the problem also occur without DPM?

BTW, in case your Mesa is built with --enable-r600-llvm-compiler, does the
problem also occur if you disable the LLVM based shader compiler with the
environment variable R600_LLVM=0 for the SL process?

(In reply to comment #7)
> Since I have no idea when the issue started happening and I can't risk
> crashing my machine dozens of times, I can't try GIT bisect myself.

That's just not true, see comment #3. Also (to preempt another concern you
mentioned on IRC), bisecting normally doesn't require any knowledge of the
code.

> I was however able to do an apitrace, which also produces the crash
> when played back.

Unfortunately, I'm not able to reproduce anything like what you describe with
that apitrace on my machines.

> I crashed my machine 5 times in order to record this.

Five iterations of git bisect would go a long way towards isolating the
problem. If you had started the bisection when you reported this bug, you would
have isolated the change introducing the problem for you a long time ago, even
if you only tested it once a day.