netdev - Re: [RFC v3 net-next 02/18] net: Clear skb->tstamp only on the forwarding path

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Message-ID: <CAF=yD-JYdh=tBcjSFCV51+EAWKQ2kR0RwgkP1ZWQesMo8caqcw@mail.gmail.com>
Date:   Wed, 7 Mar 2018 11:59:45 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Jesus Sanchez-Palencia <jesus.sanchez-palencia@...el.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiří Pírko <jiri@...nulli.us>,
        Vinicius Gomes <vinicius.gomes@...el.com>,
        Richard Cochran <richardcochran@...il.com>,
        intel-wired-lan@...ts.osuosl.org, anna-maria@...utronix.de,
        Henrik Austad <henrik@...tad.us>,
        Thomas Gleixner <tglx@...utronix.de>,
        John Stultz <john.stultz@...aro.org>,
        Levi Pearson <levi.pearson@...man.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Miroslav Lichvar <mlichvar@...hat.com>
Subject: Re: [RFC v3 net-next 02/18] net: Clear skb->tstamp only on the
 forwarding path

On Tue, Mar 6, 2018 at 8:12 PM, Jesus Sanchez-Palencia
<jesus.sanchez-palencia@...el.com> wrote:
> This is done in preparation for the upcoming time based transmission
> patchset. Now that skb->tstamp will be used to hold packet's txtime,
> we must ensure that it is being cleared when traversing namespaces.
> Also, doing that from skb_scrub_packet() would break our feature when
> tunnels are used.

Then the right location to move to is skb_scrub_packet below the test for xnet.

> Signed-off-by: Jesus Sanchez-Palencia <jesus.sanchez-palencia@...el.com>
> ---
>  include/linux/netdevice.h | 1 +
>  net/core/skbuff.c         | 1 -
>  2 files changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index dbe6344b727a..7104de2bc957 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -3379,6 +3379,7 @@ static __always_inline int ____dev_forward_skb(struct net_device *dev,
>
>         skb_scrub_packet(skb, true);
>         skb->priority = 0;
> +       skb->tstamp = 0;
>         return 0;
>  }
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 715c13495ba6..678fc5416ae1 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -4865,7 +4865,6 @@ EXPORT_SYMBOL(skb_try_coalesce);
>   */
>  void skb_scrub_packet(struct sk_buff *skb, bool xnet)
>  {
> -       skb->tstamp = 0;
>         skb->pkt_type = PACKET_HOST;
>         skb->skb_iif = 0;
>         skb->ignore_df = 0;
> --
> 2.16.2
>