panic: process 839(xmms):1 holds process lock but isn't blocked ona lock

Hi all,

I got this panic today on a: 
FreeBSD 5.3-STABLE #13: Mon Nov 29 09:49:10 CST 2004 

This panic is reproduceable via two methods:
 
1.  # kldload snd_ich

2.  add snd_ich_load="YES" to /boot/loader.conf; reboot; 
    # kldunload snd_ich

I have a kernel with debugging symbols and a vmcore if anyone is
interested. 

db> trace
kdb_enter(c068735f,c06df360,c068a355,e3744c64,c266c320) at
kdb_enter+0x32
panic(c068a355,347,c3020698,1,c0686981) at panic+0x14b
turnstile_wait(c2ef6600,c06ddec0,c3021e10,220,c06ddec0) at
turnstile_wait+0x5ec
_mtx_lock_sleep(c06ddec0,c266c320,0,c0684ceb,222) at
_mtx_lock_sleep+0xb0
_mtx_lock_flags(c06ddec0,0,c0684ceb,222,0) at _mtx_lock_flags+0xaf
ithread_loop(c2661480,e3744d48,c0684acc,323,c2661480) at
ithread_loop+0x1ea
fork_exit(c04de759,c2661480,e3744d48) at fork_exit+0xa6
fork_trampoline() at fork_trampoline+0x8
--- trap 0x1, eip = 0, esp = 0xe3744d7c, ebp = 0 ---
db> show pcpu
cpuid        = 0
curthread    = 0xc266c320: pid 28 "irq18: uhci2 bt0++"
curpcb       = 0xe3744da0
fpcurthread  = none
idlethread   = 0xc26644b0: pid 11 "idle"
APIC ID      = 0
currentldt   = 0x28
spin locks held:
db> show lockedvnods
Locked vnodes
db>

 (850)-08.12.2004 hostname-{17:26}-[/var/crash]->sudo kldunload snd_ich
Password:
lock order reversal
 1st 0xc2781a40 pcm0 (sound cdev) _at_
/usr/src/sys/modules/sound/sound/../../../dev/sound/pcm/sound.c:706
 2nd 0xc07c6a20 sndstat (sndstat) _at_
/usr/src/sys/modules/sound/sound/../../../dev/sound/pcm/sndstat.c:257
KDB: stack backtrace:
witness_checkorder(c07c6a20,9,c07c1a3d,101,0) at
witness_checkorder+0x5fa
_sx_xlock(c07c6a20,c07c1a3d,101,0,c2738e00) at _sx_xlock+0x5c
sndstat_unregister(c2753800,8,c07c1b35,2c2,c2753800) at
sndstat_unregister+0x27
pcm_unregister(c2753800,c06a5f7c,c2753800,e75e2bfc,c2753800) at
pcm_unregister+0x1f5
ich_pci_detach(c2753800,c26fd850,c06a5f7c,c07a88f1,3) at
ich_pci_detach+0x13
device_detach(c2753800,c07a8909,c26e2000,1,c26aed80) at
device_detach+0x6b