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

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Date:   Mon, 26 Sep 2016 19:02:59 +0200
From:   Jiri Benc <jbenc@...hat.com>
To:     David Ahern <dsa@...ulusnetworks.com>
Cc:     pravin shelar <pshelar@....org>,
        Simon Horman <simon.horman@...ronome.com>,
        Pravin B Shelar <pshelar@...ira.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>, buytenh@...tstofly.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>, rshearma@...cade.com,
        tom@...bertland.com, Thomas Graf <tgraf@...g.ch>,
        olivier.dugeon@...nge.com,
        Alexander Duyck <alexander.duyck@...il.com>,
        roopa@...ulusnetworks.com
Subject: Re: [PATCH net-next 2/3] net: mpls: Fixups for GSO

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.
> 
> 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