linux-kernel - Re: [PATCH NET v4 3/7] ipv6: use skb_expand_head in ip6

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Date:   Sun, 22 Aug 2021 10:04:16 -0700
From:   Christoph Paasch <christoph.paasch@...il.com>
To:     Vasily Averin <vvs@...tuozzo.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, kernel@...nvz.org,
        Julian Wiedmann <jwi@...ux.ibm.com>
Subject: Re: [PATCH NET v4 3/7] ipv6: use skb_expand_head in ip6_xmit

Hello Vasily,

On Fri, Aug 20, 2021 at 11:21 PM Vasily Averin <vvs@...tuozzo.com> wrote:
>
> On 8/21/21 1:44 AM, Christoph Paasch wrote:
> > (resend without html - thanks gmail web-interface...)
> > On Fri, Aug 20, 2021 at 3:41 PM Christoph Paasch
> >> AFAICS, this is because pskb_expand_head (called from
> >> skb_expand_head) is not adjusting skb->truesize when skb->sk is set
> >> (which I guess is the case in this particular scenario). I'm not
> >> sure what the proper fix would be though...
>
> Could you please elaborate?
> it seems to me skb_realloc_headroom used before my patch called pskb_expand_head() too
> and did not adjusted skb->truesize too. Am I missed something perhaps?
>
> The only difference in my patch is that skb_clone can be not called,
> though I do not understand how this can affect skb->truesize.

I *believe* that the difference is that after skb_clone() skb->sk is
NULL and thus truesize will be adjusted.

I will try to confirm that with some more debugging.


Christoph

>
> Thank you,
>         Vasily Averin