The games RAGE and Wolfenstein The New Order (using Wine) hangs after a short
while in the menu. 

Trying older Mesa releases (and a hacked Wine to work around the need for a
compatibility context) 17.3.9 does not have this issue.

Bisecting lead to 
bc65dcab3bc48673ff6180afb036561a4b8b1119
radeonsi: avoid syncing the driver thread in si_fence_finish
It is really only required when we need to flush for deferred fences.

It's not possibly to revert that commit cleanly on 18.2.0, but moving back "ctx
= threaded_context_unwrap_sync(ctx);" to its original place is enough to get
rid of the hang.