netdev - Re: TAHI CN-6-4-1 failed on Linux 2.6.32 kernel

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Message-ID: <AANLkTimSishHmLTQ9RF8zMq_eOBQ+HiBroKoygFS27-x@mail.gmail.com>
Date:	Fri, 20 Aug 2010 12:16:38 -0500
From:	Steve Chen <schen@...sta.com>
To:	David Miller <davem@...emloft.net>
Cc:	brian.haley@...com, usagi-users-ctl@...linux-ipv6.org,
	netdev@...r.kernel.org
Subject: Re: TAHI CN-6-4-1 failed on Linux 2.6.32 kernel

On Thu, Aug 19, 2010 at 7:06 PM, David Miller <davem@...emloft.net> wrote:
> From: Steve Chen <schen@...sta.com>
> Date: Thu, 19 Aug 2010 13:35:14 -0500
>
>> I trace through the code.  It appears that the network driver (e1000e
>> for my setup) always set ip_summed to CHECKSUM_UNNECESSARY.  I have
>> been unsuccessful to get the driver to take the other branch where
>> ip_summed is set to CHECKSUM_COMPLETE.  Even when I hard code
>> ip_summed to CHECKSUM_COMPLETE, __skb_checksum_complete_head set
>> ip_summed to CHECKSUM_UNNECESSARY after recomputing the checksum.
>>
>> So far the only way I'm able to get ICMP to recompute checksum is
>> through the attached hack.  Even though I can get all the tests to
>> pass, but it just seem wrong.
>
> If turning off hardware RX checksumming with ethtool has no effect,
> and the problem is seen with multiple ethernet cards, the problem
> is elsewhere.
>
> First of all, if you turn RX checksumming off, the checksum field
> of the SKB should always be skb->ip_summed = 0.  If this is not
> happening, find out why.

Ahhh, thats my problem.  I incorrectly thought the ip_summed should be
2.  The ip_summed is set to 1 in
__skb_checksum_complete_head.  Looking at the code, shouldn't

if (likely(!sum))

be

if (likely(sum))

Since sum == 0 would indicate an error?

Thanks

Steve
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