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From:   Eric Dumazet <edumazet@google.com>
Date:   Thu, 27 Aug 2020 04:37:08 -0700
Message-ID: <CANn89iJ7orDEWxdBJVYqhk+1WF2ZuRpzN_XOaPoGRrn2hWjGNQ@mail.gmail.com>
Subject: Re: [PATCH] net: exit immediately when off = 0 in skb_headers_offset_update()
To:     Miaohe Lin <linmiaohe@huawei.com>
Cc:     David Miller <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Pravin B Shelar <pshelar@ovn.org>,
        Florian Westphal <fw@strlen.de>, martin.varghese@nokia.com,
        Davide Caratti <dcaratti@redhat.com>,
        Steffen Klassert <steffen.klassert@secunet.com>,
        Paolo Abeni <pabeni@redhat.com>, shmulik@metanetworks.com,
        kyk.segfault@gmail.com, netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Thu, Aug 27, 2020 at 4:25 AM Miaohe Lin <linmiaohe@huawei.com> wrote:
>
> In the case of off = 0, skb_headers_offset_update() do nothing indeed.
>
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
>  net/core/skbuff.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 18ed56316e56..f67f0da20a5b 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -1459,6 +1459,8 @@ EXPORT_SYMBOL(skb_clone);
>
>  void skb_headers_offset_update(struct sk_buff *skb, int off)
>  {
> +       if (unlikely(off == 0))
> +               return;

If this is unlikely, I doubt adding a test is going to save anything.

This will instead add a conditional test for the 'likely' cases.