r259072 is not a happy camper...

I updated my "canary" machine to -current today and it's not a happy
camper.  Trying to run a buildworld on it I get the follwing reproducible
panic:

FreeBSD/amd64 (ni.freebsd.dk) (cuau0)

login: lock order reversal:
 1st 0xfffff8011641a9a0 ufs (ufs) _at_ /freebsd/head/sys/kern/vfs_lookup.c:518
 2nd 0xfffffe00e7858790 bufwait (bufwait) _at_ /freebsd/head/sys/ufs/ffs/ffs_vnops
.c:262
 3rd 0xfffff800b40ad5f0 ufs (ufs) _at_ /freebsd/head/sys/kern/vfs_subr.c:2101
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe0111361da0
kdb_backtrace() at kdb_backtrace+0x39/frampanic: bad stray interrupt
cpuid = 2
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe011120e9e0
kdb_backtrace() at kdb_backtrace+0x39/frame 0xfffffe011120ea90
vpanic() at vpanic+0x126/frame 0xfffffe011120ead0
kassert_panic() at kassert_panic+0x136/frame 0xfffffe011120eb40
intr_event_handle() at intr_event_handle+0x11d/frame 0xfffffe011120eb90
intr_execute_handlers() at intr_execute_handlers+0x48/frame 0xfffffe011120ebc0
lapic_handle_intr() at lapic_handle_intr+0x73/frame 0xfffffe011120ebf0
Xapic_isr1() at Xapic_isr1+0xa4/frame 0xfffffe011120ebf0
--- interrupt, rip = 0x11f7b11, rsp = 0x7fffffff8b50, rbp = 0x7fffffff8b80 ---
KDB: enter: panic
[ thread pid 72149 tid 100102 ]
Stopped at      kdb_enter+0x3e: movq    $0,kdb_why
db> 

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