ptcwrite panic (with dump)

I got this while pressing ^T too many times at a shell prompt on a 6.0
i386 SMP machine running current:

Fatal trap 12: page fault while in kernel mode
cpuid = 1; apic id = 00
fault virtual address   = 0x8
fault code              = supervisor read, page not present
instruction pointer     = 0x20:0xc0555fe6
stack pointer           = 0x28:0xee3e3af0
frame pointer           = 0x28:0xee3e3b4c
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, def32 1, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 822 (screen)
[thread pid 822 tid 100127 ]
Stopped at      ttyinfo+0xd6:   movl    0x8(%eax),%ebx
db> wh
Tracing pid 822 tid 100127 td 0xc3a5ad80
ttyinfo(c3602c00,0,c0704438,26f,0) at ttyinfo+0xd6
ttyinput(14,c3602c00,ee3e3c70,0,c0758880) at ttyinput+0x834
ptcwrite(c60aed00,ee3e3c70,4,556,c60aed00) at ptcwrite+0xd0
devfs_write_f(c5874d38,ee3e3c70,c3c30e80,0,c3a5ad80) at devfs_write_f+0xd4
dofilewrite(c3a5ad80,c5874d38,d,80f30e4,1) at dofilewrite+0xcb
write(c3a5ad80,ee3e3d04,c,3ff,3) at write+0x69
syscall(3b,3b,bfbf003b,0,0) at syscall+0x2a0
Xint0x80_syscall() at Xint0x80_syscall+0x1f
--- syscall (4, FreeBSD ELF32, write), eip = 0x2817873f, esp = 0xbfbfe46c, ebp = 0xbfbfe488 ---
db>
db> show registers
cs                0x20
ds          0xc0750028  legacy_pcib_methods+0x8
es          0xc0750028  legacy_pcib_methods+0x8
fs                 0x8
ss                0x28
eax                  0
ecx                0x1
edx                0x4
ebx               0x14
esp         0xee3e3af0
ebp         0xee3e3b4c
esi         0xc3602c00
edi         0xc3602c00
eip         0xc0555fe6  ttyinfo+0xd6
efl            0x10282
dr0                  0
dr1                  0
dr2                  0
dr3                  0
dr4         0xffff0ff0
dr5              0x400
dr6         0xffff0ff0
dr7              0x400
ttyinfo+0xd6:   movl    0x8(%eax),%ebx
db>

Dump shows:

#23 0xc0555fe6 in ttyinfo (tp=0xc3602c00) at ../../../kern/tty.c:2565
#24 0xc05528e4 in ttyinput (c=20, tp=0xc3602c00) at ../../../kern/tty.c:626
#25 0xc0559ef0 in ptcwrite (dev=0x0, uio=0xee3e3c70, flag=4) at linedisc.h:122
#26 0xc04cf504 in devfs_write_f (fp=0xc5874d38, uio=0xee3e3c70, cred=0xc3c30e80, flags=0, td=0x1)
---Type <return> to continue, or q <return> to quit---
    at ../../../fs/devfs/devfs_vnops.c:1367
#27 0xc054594b in dofilewrite (td=0xc3a5ad80, fp=0xc5874d38, fd=0, buf=0x0, nbyte=3228744800, offset=Unhandled dwarf expression opcode 0x93
)
    at file.h:246
#28 0xc0545779 in write (td=0xc3a5ad80, uap=0xee3e3d04) at ../../../kern/sys_generic.c:301
#29 0xc06bc280 in syscall (frame=
      {tf_fs = 59, tf_es = 59, tf_ds = -1078001605, tf_edi = 0, tf_esi = 0, tf_ebp = -1077943160, tf_isp = -297910940, tf_ebx = 135213056, tf_edx = 1, tf_ecx = 13, tf_eax = 4, tf_trapno = 0, tf_err = 2, tf_eip = 672630591, tf_cs = 51, tf_eflags = 514, tf_esp = -1077943188, tf_ss = 59})
    at ../../../i386/i386/trap.c:951
#30 0xc06a688f in Xint0x80_syscall () at ../../../i386/i386/exception.s:200
#31 0x0000003b in ?? ()