[Panic] mutex Giant not owned at sys/security/mac/mac_inet.c:217

Hello,
While playing with rpcbind/mountd/nfsd I got:

#0  doadump () at pcpu.h:165
#1  0xc04b0acb in boot (howto=0x104) at
/usr/src/sys/kern/kern_shutdown.c:397
#2  0xc04b0dcb in panic (fmt=0xc05fa8c8 "mutex %s not owned at %s:%d") at
/usr/src/sys/kern/kern_shutdown.c:553
#3  0xc04a90b8 in _mtx_assert (m=0xc0660aa0, what=0x0, file=0xc060d0ad
"/usr/src/sys/security/mac/mac_inet.c", 
    line=0xd9) at /usr/src/sys/kern/kern_mutex.c:738
#4  0xc055274b in mac_create_mbuf_from_inpcb (inp=0xc2ee2e58, m=0xc2e39b00)
at /usr/src/sys/security/mac/mac_inet.c:217
#5  0xc053bc1c in udp_output (inp=0xc2ee2e58, m=0xc2e39b00, addr=0x0,
control=0x0, td=0xc2baf600)
    at /usr/src/sys/netinet/udp_usrreq.c:765
#6  0xc053c4c2 in udp_send (so=0x0, flags=0x0, m=0xc2e39b00, addr=0x0,
control=0x0, td=0xc2baf600)
    at /usr/src/sys/netinet/udp_usrreq.c:1051
#7  0xc2ae8bc1 in ?? ()

nfsserver support was present as KLD. This problem doesn't
seem to be easily repeatable.  Curretly, I'm not able to
reproduce it.

$FreeBSD: src/sys/netinet/udp_usrreq.c,v 1.175 2005/06/01
11:24:00 rwatson Exp $
$FreeBSD: src/sys/security/mac/mac_inet.c,v 1.1 2004/02/26
03:51:04 rwatson Exp $

-- 
* Wojciech A. Koszek && dunstan_at_FreeBSD.czest.pl