12.0-RC1 drm_atomic panic (supervisor read data, protection violation)

[matias at pizarro.net]

Hello everyone,

Thanks for your great work that allows me to use a real OS on my work 
machine.

I have been tracking 12-CURRENT on a ThinkPad T450 without issues until 
now. I just got myself a T480 and rolled out 12.0-BETA4 and then RC1, 
with the same packages but I am getting a panic when launching either 
Sublime Text 3 or Textadept. All my other packages (mpv, libreoffice, 
Inkscape, Firefox, Chromium, Xfe etc...) are working fine but these two, 
which are linux binaries (relevant?), trigger the panic, both in BETA4 
and RC1, using drm-stable-kmod or drm-next-kmod, from quarterly or 
latest pkg repos.
At the moment I have
$ pkg info -d drm-next-kmod
drm-next-kmod-4.11.g20181027_1:
         gpu-firmware-kmod-g20181104

Bearing in mind these are running on different hardware:
     - works, self-compiled kernel:
         FreeBSD lenovo01 12.0-CURRENT FreeBSD 12.0-CURRENT #0 r334644 
amd64
     - panics, fresh install from BETA4 image, binary-updated to RC1:
         FreeBSD lenovo01 12.0-RC1 FreeBSD 12.0-RC1 r340470 GENERIC  
amd64

After 12 hours of trying to sort this out I have run out of ideas. I 
would appreciate it if you could help me figure out what should my next 
steps be.
I could, for instance:
     1) Roll-out 12.0-RC1 on a BE on the machine that works to see if the 
issue is linked with the change of hardware
     2) Roll-out 12-CURRENT r334644 on a BE on the panicking machine to 
see if the issue is linked to the change of kernel
     3) Compile a DEBUG kernel on the panicking machine to help you 
diagnose the issue
     4) Roll out a patched kernel if the included information inspires 
you an idea for a patch

I have no idea of C or kernel hacking but I am confortable with 
compiling custom kernels or building ports.

I have put the following in a gist, though I include here an extract of 
part of the dump report to (hopefully) whet your appetite:
     - /var/crash/core.txt, that contains full boot log, ps -axlww, 
vmstat -s | -m | -z
     - /boot/loader.conf
     - /etc/rc.conf
     - /etc/sysctl.conf
     - /var/log/Xorg.0.log (I am not using any Xorg configuration)

gist URL: 
https://gist.github.com/rebost/1a2bbfc45e9273ae5a76a98c3a67a23d

I also have the actual vmcore dump at hand if necessary, but that's 
1,4GB.

If there is anything else I can help you help me with, just let me know

Thanks for your help, past and future.

-- matías