This reproducible all the time with Dota2 starting a benchmark with 1920x1080
and Vulkan using Phoronix test suite.
Starting the benchmark makes the machine freeze and you just can hit the reset
button.
I also experienced the freeze with Shadow of Mordor but not all the time.

fc9a53946d9c107a36b79de3dd1a4eac43f13f3f is the first bad commit
commit fc9a53946d9c107a36b79de3dd1a4eac43f13f3f
Author: Junwei Zhang <Jerry.Zhang@amd.com>
Date:   Mon Jul 16 10:53:43 2018 +0800

    drm/scheduler: add NULL pointer check for run queue (v2)

    To check rq pointer before adding entity into it.
    That avoids NULL pointer access in some case.

    v2: move the check to caller

    Suggested-by: Christian König <christian.koenig@amd.com>
    Signed-off-by: Junwei Zhang <Jerry.Zhang@amd.com>
    Reviewed-by: Christian König <christian.koenig@amd.com>

:040000 040000 aa8b4eb640e3995a1f77907edd6ec8fc6fccd1b3
4a061e532ddb8a1293e781a4ccd5ece2efe35d8a M      drivers


Reverting the commit let the freeze go away.