netdev - Re: [PATCH net-next] net: preserve sock reference when scrubbing the skb.

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Date:   Tue, 26 Jun 2018 19:32:32 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        Flavio Leitner <fbl@...hat.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        David Miller <davem@...emloft.net>,
        Florian Westphal <fw@...len.de>,
        NetFilter <netfilter-devel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: preserve sock reference when scrubbing the
 skb.



On 06/26/2018 05:29 PM, Cong Wang wrote:
> On Tue, Jun 26, 2018 at 4:33 PM Flavio Leitner <fbl@...hat.com> wrote:
>>
>> It is still isolated, the sk carries the netns info and it is
>> orphaned when it re-enters the stack.
> 
> Then what difference does your patch make?
> 
> Before your patch:
> veth orphans skb in its xmit
> 
> After your patch:
> RX orphans it when re-entering stack (as you claimed, I don't know)
> 
> And for veth pair:
> xmit from one side is RX for the other side
> 
> So, where is the queueing? Where is the buffer bloat? GRO list??
> 

By re-entering the stack, Flavio probably meant storing this skb in
a socket receive queue, or anything that should already modify skb->destructor
(and thus call skb_orphan() before the modification)

If skb sits in some qdisc, like fq on ipvlan master device, we do not want skb->sk to be scrubbed,
just because ipvlan slave and master might be in different netns.