Panic on amd64: _mtx_lock_sleep: recursed on non-recursive mutex

[Willem Jan Withagen]

panic: _mtx_lock_sleep: recursed on non-recursive mutex UMA pcpu @ 
/home1/src/sys/vm/uma_core.c:1800
db> trace
kdb_enter() at kdb_enter+0x31
panic() at panic+0x1e6
uma_dbg_free() at uma_dbg_free+0x130
uma_zfree_arg() at uma_zfree_arg+0x121
m_freem() at m_freem+0x41
em_clean_transmit_interrupts() at em_clean_transmit_interrupts+0xea
em_intr() at em_intr+0x10c
ithread_loop() at ithread_loop+0x179
fork_exit() at fork_exit+0xe9
fork_trampoline() at fork_trampoline+0xe
--- trap 0, rip = 0, rsp = 0xffffffffb1bb9d00, rbp = 0 ---

uname -a
FreeBSD opteron.digiware.nl 5.3-BETA7 FreeBSD 5.3-BETA7 #145: Wed Oct 13 
14:03:44 CEST 2004 
root at opteron.digiware.nl:/usr/obj/home1/src/sys/OPTERON.amd64  amd64

dumping core has not worked, for whatever reason there seems no image on swap :(
I'll try to get more when it reoccurs

--WjW