This bug is still alive for me.

Have randomly tested and reproduced since reporting and failed to reproduce
with 

6327b584155d040ae089e65fd6747186bdd9666b reverted.

Just retried with the new agd5f drm-next-319-wip and it's still there - though
this time I got and oops which mentions radeon/ttm so uploading.

To produce I am running a script running mplayer on various blu-rays on hard
disk.

It's not aggressive - run for 10 sec sleep for three ....

I added a counter and it got up to 29 before oopsing.