# Re: \[PATCH net-next 2/3\] net: mpls: Fixups for GSO

- From: David Ahern \<hidden\>
- Date: 2016-09-27 02:04:09 
- List: netdev
- Page: https://ratatoskr.run/netdev/2016/09/11030594
- Thread: https://ratatoskr.run/netdev/2016/08/11026023/t.md

```text
On 9/26/16 11:02 AM, Jiri Benc wrote:
> On Mon, 26 Sep 2016 17:56:22 +0200, Jiri Benc wrote:
>> After push_mpls, network_header points to the start of MPLS headers.
>> Which I understand was the point of this patch. However, push_mpls also
>> calls invalidate_flow_key. Meaning that, depending on actions, we may
>> end up calling key_extract soon after. And key_extract sets the network
>> header *after* the MPLS headers.

you know this code better than me, but key_extract pulls the eth header and then sets network header. If MPLS labels are present then it is the labels that the network_header now points to. How did come to the conclusion it is after the labels?

>>
>> That means that on output, for otherwise identical packet,
>> network_header can point before or after MPLS headers based on what
>> actions happened to be executed (recirculation, mainly).
>>
>> If I'm not misreading the code or missing something, this can't be
>> right.
>>
>> mpls_gso_segment does not care, it resets the network_header anyway.
>> What about drivers? What is the correct behavior?
> 
> Answering to myself: it breaks skb_mac_gso_segment. Seems we need to
> fix key_extract to set network_header to the beginning of MPLS headers.
> I'll prepare a patch.
> 
>  Jiri
> 
```