(In reply to Michel Dänzer from comment #5)
> http://lists.freedesktop.org/archives/dri-devel/2015-June/084514.html fixes
> the hang for me (not a GPU hang but a kernel hang, because it tries to lock
> a mutex that's already locked).
> 
> 
> > [  141.232226] radeon 0000:01:00.0: bo ffff8804236d3400 va 0x0000001000
> > conflict with (bo ffff88042a018800 0x0000001000 0x0000001563)
> 
> These still happen, but at least with GNOME it continues working for me
> somehow. I tried various workarounds for this in the Xorg driver, but I
> haven't found anything that avoids these. I think the proper solution for
> these would be for the kernel driver to track GPU VA ranges per GEM handle
> instead of per BO.

The latest patch applied to linux kernel rc8 fixed this issue, thanks.