kern/40137: gem(4) drops TCP packets with tcp4csum-tx when on a bridge(4)

[Taylor R Campbell <campbell%mumble.net@localhost>]

>Number:         40137
>Category:       kern
>Synopsis:       gem(4) drops TCP packets with tcp4csum-tx when on a bridge(4)
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Dec 09 07:40:00 +0000 2008
>Originator:     Taylor R Campbell <campbell%mumble.net@localhost>
>Release:        NetBSD 4.0_STABLE
>Organization:
>Environment:
System: NetBSD slate.localdomain 4.0_STABLE NetBSD 4.0_STABLE (RIABWI) #35: Sun 
Nov 16 12:42:48 EST 2008 
riastradh%Oberon.local@localhost:/Users/riastradh/os/netbsd/4/obj/sys/arch/macppc/compile/RIABWI
 macppc
Architecture: powerpc
Machine: macppc

        (My `RIABWI' kernel contains the bwi(4) driver and enables
        cgd(4), OFB_ENABLE_CACHE, and CAPS_IS_CONTROL; otherwise it is
        identical to GENERIC.  The only bwi(4) interface is down as I
        test this problem.)

>Description:

        Enabling tcp4csum-tx on a gem(4) interface, and adding that
        interface to a bridge(4), causes the gem(4) interface to drop
        incoming TCP packets.  Neither alone exhibits the problem; only
        the combination of circumstances does.

>How-To-Repeat:

        On a machine with a gem(4) interface, enable the tcp4csum-tx
        option, create a bridge(4) interface, and add the gem(4)
        interface to it.  Run tcpdump(8) on the gem(4) interface and
        initiate a TCP connection on the gem(4) interface; observe the
        outgoing, but not incoming, TCP packets.

>Fix:

        None known.