panic: trying to sleep while sleeping is prohibited (from ttyinfo)

I just got this panic from my 7.0-CURRENT laptop (Thinkpad T20),
cvsup'd as of Oct 11.  I was editing a file in vi at the time.

-ed

root_at_laptop# uname -a
FreeBSD laptop 7.0-CURRENT FreeBSD 7.0-CURRENT #3: Tue Oct 11 18:03:58 EDT 2005
    emaste_bsd-build.phaedrus.sandvine.com:/d2/emaste/head/obj/d2/emaste/head/sr
c/sys/GENERIC  i386

(kgdb) bt
[...]
#9  0xc063805f in panic (
    fmt=0xc0867c0a "trying to sleep while sleeping is prohibited")
    at /d2/emaste/head/src/sys/kern/kern_shutdown.c:539
#10 0xc065555c in sleepq_add (wchan=0xc092e764, lock=0xc092e1c0,
    wmesg=0x12 <Address 0x12 out of bounds>, flags=1)
    at /d2/emaste/head/src/sys/kern/subr_sleepqueue.c:273
#11 0xc0613636 in cv_wait (cvp=0xc092e764, mp=0xc092e1c0)
    at /d2/emaste/head/src/sys/kern/kern_condvar.c:127
#12 0xc063d0a0 in _sx_slock (sx=0xc092e740,
    file=0xc086adef "/d2/emaste/head/src/sys/kern/tty.c", line=2564)
    at /d2/emaste/head/src/sys/kern/kern_sx.c:122
#13 0xc06691f0 in ttyinfo (tp=0xc1bac000)
    at /d2/emaste/head/src/sys/kern/tty.c:2564
#14 0xc066627e in ttyinput (c=20, tp=0xc1bac000)
    at /d2/emaste/head/src/sys/kern/tty.c:626
#15 0xc07da749 in sckbdevent (thiskbd=0xc098afa0, event=0, arg=0xc09aee80)
    at linedisc.h:122
#16 0xc07b6d74 in atkbd_intr (kbd=0xc098afa0, arg=0x0)
    at /d2/emaste/head/src/sys/dev/atkbdc/atkbd.c:486
#17 0xc07b7e6a in atkbdintr (arg=0xc1033000)
    at /d2/emaste/head/src/sys/dev/atkbdc/atkbd_atkbdc.c:174
#18 0xc06258bc in ithread_loop (arg=0xc19d8900)
    at /d2/emaste/head/src/sys/kern/kern_intr.c:547
#19 0xc0624cc8 in fork_exit (callout=0xc0625778 <ithread_loop>,
    arg=0xc19d8900, frame=0xd44a5d38)
    at /d2/emaste/head/src/sys/kern/kern_fork.c:789
#20 0xc07e780c in fork_trampoline ()
    at /d2/emaste/head/src/sys/i386/i386/exception.s:208

(kgdb) frame 12
[...]
(kgdb) p *sx
$2 = {sx_object = {lo_class = 0xc08cc8ac, lo_name = 0xc0864442 "proctree",
    lo_type = 0xc0864442 "proctree", lo_flags = 3866624, lo_list = {
      tqe_next = 0xc092e780, tqe_prev = 0xc092e710},
    lo_witness = 0xc093fa38}, sx_lock = 0xc092e1c0, sx_cnt = -1,
  sx_shrd_cv = {cv_description = 0xc0864442 "proctree", cv_waiters = 1},
  sx_shrd_wcnt = 1, sx_excl_cv = {cv_description = 0xc0864442 "proctree",
    cv_waiters = 0}, sx_excl_wcnt = 0, sx_xholder = 0xc344d300}