kern/45764: ifconfig stf0 destroy is unhealthy

[spz%NetBSD.org@localhost]

>Number:         45764
>Category:       kern
>Synopsis:       ifconfig stf0 destroy caused a panic
>Confidential:   no
>Severity:       serious
>Priority:       low
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Dec 31 22:15:00 +0000 2011
>Originator:     S.P.Zeidler
>Release:        NetBSD 5.1_STABLE
>Organization:
        TNF
>Environment:
System: NetBSD morden.NetBSD.org 5.1_STABLE NetBSD 5.1_STABLE (NBFTP) #17: Sat 
Dec 24 15:46:47 UTC 2011 
root%franklin.NetBSD.org@localhost:/home/netbsd/5/amd64/kern-compile/NBFTP amd64
Architecture: x86_64
Machine: amd64
>Description:
        fatal protection fault in supervisor mode
        trap type 4 code 0 rip ffffffff8017e065 cs 8 rflags 10282 cr2  
7f7ffd618020 cpl 6 rsp ffff80004f0076c0
        kernel: protection fault trap, code=0
        Stopped in pid 12552.1 (ifconfig) at    netbsd:nd6_purge+0xd5:  cmpb    
$0x12,0x1(%rax)
        db{0}> bt
        nd6_purge() at netbsd:nd6_purge+0xd5
        in6_ifdetach() at netbsd:in6_ifdetach+0x21
        in6_purgeif() at netbsd:in6_purgeif+0x25
        udp6_usrreq() at netbsd:udp6_usrreq+0xfd
        udp6_usrreq_wrapper() at netbsd:udp6_usrreq_wrapper+0x51
        if_detach() at netbsd:if_detach+0x2b0
        stf_clone_destroy() at netbsd:stf_clone_destroy+0x4c
        if_clone_destroy() at netbsd:if_clone_destroy+0x44
        ifioctl() at netbsd:ifioctl+0x1a3
        soo_ioctl() at netbsd:soo_ioctl+0x246
        sys_ioctl() at netbsd:sys_ioctl+0x138
        syscall() at netbsd:syscall+0xa0

>How-To-Repeat:
        strict repeatability has not been tested
        ifconfig stf0 create
        ifconfig stf0 inet6 2002:c7e9:d9f9::21/16 alias deprecated link0
        [wait a while]
        ifconfig stf0 destroy
>Fix:
        left as an exercise for now