Forced crash dump taken while the livelock was active (guest, stock kernel):
  # sysctl -w debug.debugger_on_panic=0
  # sysctl -w debug.panic=1
  panic: sysctl_debug_panic
  cpuid = 5
  ...
  Dumping 681 MB: ...
  Dump complete
(/var/crash/vmcore.0 — minidump; stock gdb 7.6.1 in guest cannot load
 DFly minidumps, so no offline bt; the live observations in
 livelock-evidence.txt (R0 forever, kill -9 ineffective, D-state
 collateral, blocked rm diagnostic, 3 hung shutdowns) carry the proof.)

Serial console diagnostics captured before the wedge killed the console:
  [diagnostic] cache_lock_shared: rm blocked on 0xfffff8008f54dc00 "df2921.bin"
  Sep  3 11:56:41 dfbsd shutdown: power-down by root:
  Sep  3 11:58:27 dfbsd shutdown: power-down by root:
  Sep  3 12:00:10 dfbsd shutdown: power-down by root: