Infinite loop in devfs_create()

I have an SMP amd64 package machine that has deadlocked, apparently
here:

--- trap 0x13, rip = 0xffffffff8034b2a1, rsp = 0xffffffffbe6f2a10, rbp = 0xffffffffbe6f2a40 ---
devfs_create() at devfs_create+0x41
make_dev_credv() at make_dev_credv+0x148
make_dev() at make_dev+0x97
g_dev_taste() at g_dev_taste+0x130
g_new_provider_event() at g_new_provider_event+0x8a
one_event() at one_event+0x19b
g_run_events() at g_run_events+0x9
g_event_procbody() at g_event_procbody+0x7d
fork_exit() at fork_exit+0xdf
fork_trampoline() at fork_trampoline+0xe
--- trap 0, rip = 0, rsp = 0xffffffffbe6f2d00, rbp = 0 ---

If I break/continue and examine devfs_nextino, it appears to be
looping infinitely in devfs_create:

db> x/d devfs_nextino
devfs_nextino:  746
[...]
db> x/d devfs_nextino
devfs_nextino:  339

This machine has a number of md mounts active (they are created and
destroyed dynamically and tend to get up to high unit numbers, around
~600 at the time of deadlock).  Also devfs mounts come and go, but I
don't think anything else unusual is going on on the system.

Kris