kern/39794: panic (in4_cksum: bad mbuf chain) when using ftp

[jaapb%kerguelen.org@localhost]

        Note: There was a bad value `kern' for the field `Class'.
        It was set to the default value of `sw-bug'.

>Number:         39794
>Category:       kern
>Synopsis:       panic (in4_cksum: bad mbuf chain) when using ftp
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Oct 24 14:05:00 +0000 2008
>Originator:     jaapb%kerguelen.org@localhost
>Release:        NetBSD 4.0_STABLE (retrieved from CVS Oct. 23)
>Organization:
        
>Environment:
        
        
System: NetBSD courbet.kerguelen.org 4.0_STABLE NetBSD 4.0_STABLE (COURBET) #4: 
Thu Oct 23 20:18:19 CEST 2008 
root%courbet.kerguelen.org@localhost:/usr/obj/sys/arch/amd64/compile/COURBET 
amd64
Architecture: x86_64
Machine: amd64
>Description:
When I've got ipnat enabled and use ftp (the client), I get a panic with
in4_cksum: bad mbuf chain.

Its backtrace:
in4_cksum
tcp_input_cksum
tcp_input
ip_input
ipintr

The problem is probably related to 
http://mail-index.netbsd.org/current-users/2008/04/18/msg001865.html (I've 
verified: it also occurs on a very recent current
(Oct 20, say) for sparc64/SMP). 

The machine I am running this on (amd64) is also a SMP (well, multicore) 
machine.
>How-To-Repeat:
A make fetch in databases/p5-DBD-postgresql triggers the problem for me
reliably, but any ftp activity with ipnat should do.
>Fix:
n/a

>Unformatted: