panic: sbdrop in sbcut_internal

Seen this on head while doing two `/etc/rc.d/netif restart wlan0' in parallel.
Thanks our shiny new compiler I can not examine local vars.

     $FreeBSD: head/sys/kern/uipc_sockbuf.c 256185 2013-10-09
11:57:53Z glebius $

Unread portion of the kernel message buffer:
<118>Nov 24 20:35:52 omg wpa_supplicant[55133]: ioctl[SIOCS80211,
op=26, val=0, arg_len=0]: Operation not supported
panic: sbdrop
cpuid = 0

#2  0xffffffff805904b4 in panic (fmt=<value optimized out>)
    at /usr/src/sys/kern/kern_shutdown.c:754
#3  0xffffffff805fe2eb in sbcut_internal (sb=<value optimized out>,
    len=<value optimized out>) at /usr/src/sys/kern/uipc_sockbuf.c:859
#4  0xffffffff805fd368 in sbflush_internal (sb=0xfffff8000b4b0348)
    at /usr/src/sys/kern/uipc_sockbuf.c:821
#5  0xffffffff805fd4a2 in sbdestroy (sb=0xfffff8000b4b0348,
    so=0xfffff8000b4b02b8) at /usr/src/sys/kern/uipc_sockbuf.c:339
#6  0xffffffff805ff300 in sofree (so=0xfffff8000b4b02b8)
    at /usr/src/sys/kern/uipc_socket.c:752
#7  0xffffffff805ff7d2 in soclose (so=<value optimized out>)
    at /usr/src/sys/kern/uipc_socket.c:837
#8  0xffffffff805502f9 in _fdrop (fp=0xfffff8000b4d5370, td=0x0) at file.h:342
#9  0xffffffff80552b97 in closef (fp=<value optimized out>,
    td=<value optimized out>) at /usr/src/sys/kern/kern_descrip.c:2315
#10 0xffffffff805505f5 in closefp (fdp=0xfffff8000b3bb800,
    fd=<value optimized out>, fp=0xfffff8000b4d5370, td=0xfffff8000b036490,
    holdleaders=<value optimized out>) at /usr/src/sys/kern/kern_descrip.c:1159
#11 0xffffffff807c23c7 in amd64_syscall (td=0xfffff8000b036490, traced=0)
    at subr_syscall.c:134

(kgdb) f 3
#3  0xffffffff805fe2eb in sbcut_internal (sb=<value optimized out>,
    len=<value optimized out>) at /usr/src/sys/kern/uipc_sockbuf.c:859
859                    panic("sbdrop");
(kgdb) list
854        mfree = NULL;
855
856        while (len > 0) {
857            if (m == 0) {
858                if (next == 0)
859                    panic("sbdrop");
860                m = next;
861                next = m->m_nextpkt;
862                continue;
863            }

-- 
wbr,
pluknet