Created attachment 139418 [details]
Relevant fragment of dmesg when this occurs

I sometimes (for seemingly no reason at all) have the graphics completely hang
on my machine. I lose my keyboard as well, although my machine is still running
(I can SSH into it and everything else still works). I can still move the
mouse, but nothing visual responds (I can't click on anything, can't change
active windows, etc). 

Some additional points of interest:

- My DisplayPort monitor blacks out in such a case, while my DVI monitor keeps
working (displaying the same still image)
- Killing X or my WM has no effect on this once it occurs (only a restart fixes
it)
- I can't determine if any particular thing triggers it (seems totally
arbitrary)

I've attached a dmesg fragment from one such incident, as well as other
pertinent information. Its mention of AMDGPU is why I reported this bug here.