bogus 0 len IP packet, was: Hang in VOP_LOCK1_APV on 8-STABLE with NFS.

[sthaug at nethelp.no]

> > So, does anyone have an idea why the IP length field would be set to 0
> > for these TCP/IP packets?
> > 
> > Here's some info from Ronald w.r.t. his hardware. (All I can think of is
> > that he could try disabling TSO, etc?)
> > 
> > Thanks in advance for any help with this, rick
> > 
> 
> It seems that issue came from TSO. Driver will set ip_len and
> ip_sum field to 0 before passing the TCP segment to controller.
> The failed length were 4446, 5858, 3034 and 4310 and the total
> number of such frames are more than 35k within 90 seconds. Since
> failed length 4310 is continuously repeated I guess there is edge
> case where em(4) didn't free failed TCP segment for TSO.
> I remember there was commit to HEAD(r217295) which could be related
> with this issue.

I'm seeing the same problem with Broadcom NetXtreme (bce) cards:

bce0 at pci0:3:0:0:        class=0x020000 card=0x03421014 chip=0x164c14e4 rev=0x12 hdr=0x00
    vendor     = 'Broadcom Corporation'
    device     = 'Broadcom NetXtreme II Gigabit Ethernet Adapter (BCM5708)'
    class      = network
    subclass   = ethernet

This is with 8.2-PRERELEASE. Turning off TSO (ifconfig bce0 -tso)
removes the problem.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no