Unloading if_em causes panic on 8.0-BETA2 #0 r195818 (i386)

System: 
FreeBSD RabbitsDen.RabbitsLawn.verizon.net 8.0-BETA2 FreeBSD 8.0-BETA2
#0 r195818: Wed Jul 22 13:50:22 EDT 2009
root_at_RabbitsDen.RabbitsLawn.verizon.net:/usr/obj/usr/src/sys/TPX60  i386

To reproduce: 
kldload if_em; kldunload if_em

Hardware:
em0_at_pci0:2:0:0:	class=0x020000 card=0x207e17aa chip=0x109a8086 rev=0x00
hdr=0x00
    vendor     = 'Intel Corporation'
    device     = 'Intel PRO/1000 PL Network Adaptor (82573L)'
    class      = network
    subclass   = ethernet

Crash summary: 
http://members.verizon.net/~akovalenko/Misc/core.txt.0

Backtrace:
(kgdb) bt
#0  doadump () at pcpu.h:246
#1  0xa0586614 in boot (howto=260)
at /usr/src/sys/kern/kern_shutdown.c:419
#2  0xa058692b in panic (fmt=Variable "fmt" is not available.
) at /usr/src/sys/kern/kern_shutdown.c:575
#3  0xa0712fe1 in vm_fault (map=0xa1090000, vaddr=2701840384,
fault_type=1 '\001', fault_flags=0) at /usr/src/sys/vm/vm_fault.c:283
#4  0xa076e046 in trap_pfault (frame=0xfa528adc, usermode=0,
eva=2701844432) at /usr/src/sys/i386/i386/trap.c:835
#5  0xa076ebab in trap (frame=0xfa528adc)
at /usr/src/sys/i386/i386/trap.c:528
#6  0xa075281b in calltrap () at /usr/src/sys/i386/i386/exception.s:165
#7  0xa057204d in free (addr=0xaefcb000, mtp=0xa07fbcd0) at
vm_page.h:255
#8  0xa05b1978 in buf_ring_free (br=0xaefcb000, type=0xa07fbcd0)
at /usr/src/sys/kern/subr_bufring.c:67
#9  0xaeff86aa in em_free_transmit_structures (adapter=0xaefc6000)
at /usr/src/sys/modules/em/../../dev/e1000/if_em.c:3647
#10 0xaeffb10f in em_detach (dev=0xa6250400)
at /usr/src/sys/modules/em/../../dev/e1000/if_em.c:925
#11 0xa05af62d in device_detach (dev=0xa6250400) at device_if.h:212
#12 0xa05afaba in driver_module_handler (mod=0xa7908e00, what=1,
arg=0xaf01b81c) at /usr/src/sys/kern/subr_bus.c:1098
#13 0xa05742fd in module_unload (mod=0xa7908e00)
at /usr/src/sys/kern/kern_module.c:266
#14 0xa056b65d in linker_file_unload (file=0xaefaf400, flags=0)
at /usr/src/sys/kern/kern_linker.c:632
#15 0xa056c0e4 in kern_kldunload (td=0xab050900, fileid=27, flags=0)
at /usr/src/sys/kern/kern_linker.c:1091
#16 0xa056c161 in kldunloadf (td=0xab050900, uap=0xfa528cf8)
at /usr/src/sys/kern/kern_linker.c:1121
#17 0xa076e474 in syscall (frame=0xfa528d38)
at /usr/src/sys/i386/i386/trap.c:1073
#18 0xa07528b0 in Xint0x80_syscall ()
at /usr/src/sys/i386/i386/exception.s:261
#19 0x00000033 in ?? ()
Previous frame inner to this frame (corrupt stack?)
(kgdb) 

Please, let me know if there is anything else I can provide. 

-- 
Alexandre Kovalenko (Олександр Коваленко)