Thanks for the quake 2 trace, I could reproduce the same hang here.

If anyone has a reliable way to trigger the issue, the most helpful thing to do
for now is an apitrace capture.

The umr log were helpful (thanks!) but I don't need more of them at the moment.

I don't think radv uses SDMA at all, so they cannot be affected by this issue. 
For radeonsi the AMD_DEBUG=nodma environment variable is a workaround until we
figure out a proper fix.