Run 1 (stock kernel): 
  $ ./fsetown_race 20000
  DF-2683: uid=1001 racing fsetown() publication against exit-teardown for 20000 rounds...
  [ssh session dies; guest unresponsive; QEMU alive ~3 vCPUs spinning; no serial
   output; no reboot -- machine wedge variant]

Run 2 (stock kernel, fresh vm.sh reset with-src):
  $ ./fsetown_race 20000
  DF-2683: uid=1001 racing fsetown() publication against exit-teardown for 20000 rounds...
  round 0 (162 sets)
  [ssh dies here; serial console records the fatal trap -- panic.txt]