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Date:   Mon, 9 Nov 2020 20:05:22 -0800
From:   Jakub Kicinski <kuba@kernel.org>
To:     Alexander Lobakin <alobakin@pm.me>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Martin Varghese <martin.varghese@nokia.com>,
        Pravin B Shelar <pshelar@ovn.org>,
        Willem de Bruijn <willemb@google.com>,
        Guillaume Nault <gnault@redhat.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Florian Westphal <fw@strlen.de>,
        Steffen Klassert <steffen.klassert@secunet.com>,
        Paolo Abeni <pabeni@redhat.com>,
        Yadu Kishore <kyk.segfault@gmail.com>,
        Vladimir Oltean <vladimir.oltean@nxp.com>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 net-next] net: skb_vlan_untag(): don't reset
 transport offset if set by GRO layer
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References: <7JgIkgEztzt0W6ZtC9V9Cnk5qfkrUFYcpN871syCi8@cp4-web-040.plabs.ch>
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On Mon, 09 Nov 2020 23:47:23 +0000 Alexander Lobakin wrote:
> Similar to commit fda55eca5a33f
> ("net: introduce skb_transport_header_was_set()"), avoid resetting
> transport offsets that were already set by GRO layer. This not only
> mirrors the behavior of __netif_receive_skb_core(), but also makes
> sense when it comes to UDP GSO fraglists forwarding: transport offset
> of such skbs is set only once by GRO receive callback and remains
> untouched and correct up to the xmitting driver in 1:1 case, but
> becomes junk after untagging in ingress VLAN case and breaks UDP
> GSO offload. This does not happen after this change, and all types
> of forwarding of UDP GSO fraglists work as expected.
> 
> Since v1 [1]:
>  - keep the code 1:1 with __netif_receive_skb_core() (Jakub).
> 
> [1] https://lore.kernel.org/netdev/zYurwsZRN7BkqSoikWQLVqHyxz18h4LhHU4NFa2Vw@cp4-web-038.plabs.ch
> 
> Signed-off-by: Alexander Lobakin <alobakin@pm.me>

Applied, thanks!