Comment # 13 on bug 109692 from Andrey Grodzovsky

Also, in the meanwhile try reverting this 2 patches and see if it helps - 

3741540 Andrey Grodzovsky   5 weeks ago    drm/sched: Rework HW fence
processing.   
222b5f0 Andrey Grodzovsky   5 weeks ago    drm/sched: Refactor ring mirror list
handling.  

They are causing this deadlock.