First is caused by this commit while running a GL heavy application.

d78c1fa0c9f815fe951fd57001acca3d35262a17 is the first bad commit
commit d78c1fa0c9f815fe951fd57001acca3d35262a17
Author: Michel Dänzer <michel.daenzer-5C7GfCeVMHo@public.gmane.org>
Date:   Wed Aug 29 11:59:38 2018 +0200

     Revert "drm/amdgpu: move PD/PT bos on LRU again"

     This reverts commit 31625ccae4464b61ec8cdb9740df848bbc857a5b.

     It triggered various badness on my development machine when running the
     piglit gpu profile with radeonsi on Bonaire, looks like memory
     corruption due to insufficiently protected list manipulations.

     Signed-off-by: Michel Dänzer <michel.daenzer-5C7GfCeVMHo@public.gmane.org>
     Signed-off-by: Alex Deucher <alexander.deucher-5C7GfCeVMHo@public.gmane.org>

:040000 040000 b7169f0cf0c7decec631751a9896a92badb67f9d 
42ea58f43199d26fc0c7ddcc655e6d0964b81817 M      drivers

The second is caused by something between that and the tip of the 
4.19-rc1 amd-staging-drm-next (I haven't pinned it down yet) while 
loading GNOME.

Tom