Oh, the hang in comment 1 may have been my fault for running it with hyperz.

But without hyperz it hangs too, just less verbosely:

radeon 0000:01:00.0: ring 3 stalled for more than 10016msec
radeon 0000:01:00.0: GPU lockup (waiting for 0x0000000000011c4a last fence id
0x0000000000011b2a on ring 3)
[TTM] Buffer eviction failed