crash in tty code in 6.1.. fixed since?

Does this crash look familiar to anyone?
It's in 6.1 unfortunatly..

#6  0xc069ca6a in calltrap () at ../../../i386/i386/exception.s:139
#7  0xc0587012 in ttymodem (tp=0xc6990800, flag=-1065963704)
    at ../../../kern/tty.c:1659
#8  0xc058b83e in ptcclose (dev=0x0, flags=7, fmt=8192, td=0xc6966d80)
    at linedisc.h:136
#9  0xc052bf77 in giant_close (dev=0xc7547c00, fflag=7, devtype=8192, 
    td=0xc6966d80) at ../../../kern/kern_conf.c:266
#10 0xc051685f in devfs_close (ap=0xe706baa4)
    at ../../../fs/devfs/devfs_vnops.c:287
#11 0xc06c2a10 in VOP_CLOSE_APV (vop=0x0, a=0xc076af48) at vnode_if.c:426
#12 0xc05bf3ce in vn_close (vp=0xc764e550, flags=7, file_cred=0x0, 
    td=0xc6966d80) at vnode_if.h:227
#13 0xc05c0212 in vn_closefile (fp=0xc7532510, td=0xc6966d80)
    at ../../../kern/vfs_vnops.c:852
#14 0xc0516887 in devfs_close_f (fp=0xc7532510, td=0xc6966d80)
    at ../../../fs/devfs/devfs_vnops.c:297
#15 0xc05361e8 in fdrop_locked (fp=0xc7532510, td=0xc6966d80) at file.h:289
#16 0xc0536135 in fdrop (fp=0xc7532510, td=0xc6966d80)
    at ../../../kern/kern_descrip.c:2122
#17 0xc05346d3 in closef (fp=0xc7532510, td=0xc6966d80)
    at ../../../kern/kern_descrip.c:1942
#18 0xc0533487 in fdfree (td=0xc6966d80) at ../../../kern/kern_descrip.c:1627
#19 0xc053cc88 in exit1 (td=0xc6966d80, rv=15) at ../../../kern/kern_exit.c:263
#20 0xc055b58b in sigexit (td=0xc6966d80, sig=15)
    at ../../../kern/kern_sig.c:2451
#21 0xc055b296 in postsig (sig=15) at ../../../kern/kern_sig.c:2326
#22 0xc0577fbe in ast (framep=0xe706bd38) at ../../../kern/subr_trap.c:266
#23 0xc069d3ad in doreti_ast () at ../../../i386/i386/exception.s:293

(kgdb) up
#7  0xc0587012 in ttymodem (tp=0xc6990800, flag=-1065963704)
    at ../../../kern/tty.c:1659
1659                                    if (tp->t_session->s_leader) {
Current language:  auto; currently c
(kgdb) list
1654                        !ISSET(tp->t_cflag, CLOCAL)) {
1655                            SET(tp->t_state, TS_ZOMBIE);
1656                            CLR(tp->t_state, TS_CONNECTED);
1657                            if (tp->t_session) {
1658                                    sx_slock(&proctree_lock);
1659                                    if (tp->t_session->s_leader) {
1660                                            struct proc *p;
1661
1662                                            p = tp->t_session->s_leader;
1663                                            PROC_LOCK(p);

(kgdb) set print pretty
(kgdb) p *tp
$3 = {
  t_rawq = {
    c_cc = 0, 

 [...]

  t_outcc = 119661, 
  t_line = 0, 
  t_dev = 0xc763fe00, 
  t_mdev = 0x0, 
  t_devunit = 0, 
  t_state = 0, 
  t_flags = 0, 
  t_timeout = 300000, 
  t_pgrp = 0x0, 
  t_session = 0x0, 
  t_sigio = 0x0, 
  t_rsel = {
    si_thrlist = {
      tqe_next = 0x0, 
      tqe_prev = 0x0
    }, 
    si_thread = 0x0, 
    si_note = {
    
[...]


tp_session is NULL but it shouldn't have been able to have 
run that line (line 1659) if it had tested NULL 2 lines before..
this suggests a locking problem..