netdev - Re: [LKP] [net] 2ab9fb18c4: kernel BUG at include/linux/skbuff.h:1935!

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Date:   Tue, 15 Nov 2016 10:30:15 -0800
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Fengguang Wu <fengguang.wu@...el.com>
Cc:     Ye Xiaolong <xiaolong.ye@...el.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        Willem de Bruijn <willemb@...gle.com>,
        netdev <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Jojy Varghese <jojvargh@...co.com>,
        Tom Herbert <tom@...bertland.com>,
        Yibin Yang <yibyang@...co.com>, LKP <lkp@...org>,
        David Miller <davem@...emloft.net>
Subject: Re: [LKP] [net] 2ab9fb18c4: kernel BUG at include/linux/skbuff.h:1935!

On Sun, Nov 13, 2016 at 7:11 PM, Fengguang Wu <fengguang.wu@...el.com> wrote:
>>> Hi guys.
>>>
>>> I took a look at the commit again and I do not see how this can happen.
>>>
>>> Are you sure patch was properly applied ?
>>>
>>> In particular, the following extract is obscure for me :
>>>
>>>
>>>> https://github.com/0day-ci/linux
>>>> Eric-Dumazet/net-__skb_flow_dissect-must-cap-its-return-value/20161110-080839
>>>> commit 2ab9fb18c46b91b16a0f0f329336d3be9fc32deb ("net:
>>>> __skb_flow_dissect() must cap its return value")
>>>>
>>
>> Hi,
>>
>> The above two lines means 0day repo setup a new branch
>>
>> "Eric-Dumazet/net-__skb_flow_dissect-must-cap-its-return-value/20161110-080839"
>> which is based on net/master, then applied you patch on top of it,
>> commit id is 2ab9fb18c46b91b16a0f0f329336d3be9fc32deb.
>
>
> Xiaolong, it may be more helpful to show the base tree where we apply
> the patch to. And the final url:
>
> https://github.com/0day-ci/linux/tree/Eric-Dumazet/net-__skb_flow_dissect-must-cap-its-return-value/20161110-080839
>
> Thanks,
> Fengguang

Is there any chance you guys could send me the net/ethernet/eth.o and
drivers/net/ethernet/intel/igb/igb.o files for this build?  I'm still
not able to reproduce but I have a thought that this might be some
sort of compiler issue.

Specifically looking over the call trace it looks like we only pulled
8 bytes of the header instead of 14.  This is based on the values of
RAX and R15 differing by 6 which I believe represent skb->len and
skb->data_len  However eth_get_headlen is supposed to be using
sizeof(*eth) which should be 14.  I'm wondering if there is an issue
due to it being a packed structure that is resulting in 8 being
reported instead of 14.

Thanks.

- Alex