https://bugs.freedesktop.org/show_bug.cgi?id=92258
--- Comment #4 from Christian König deathsimple@vodafone.de --- The crash looks like the TTM cleanup process tries to free a buffer twice.
Most likely a bug in the reference counting somewhere. Can you try to bisect the DRM changes between 4.1.6 and 4.1.7?
According to the git logs there wasn't even a single change radeon between 4.1.6 and 4.1.7 so this sounds like a problem in TTM.