netdev - Re: [PATCH net-next] net: loopback: clear skb->tstamp before netif

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Date:   Fri, 19 Oct 2018 22:29:30 -0400
From:   Soheil Hassas Yeganeh <soheil@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next] net: loopback: clear skb->tstamp before netif_rx()

On Fri, Oct 19, 2018 at 10:11 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> At least UDP / TCP stacks can now cook skbs with a tstamp using
> MONOTONIC base (or arbitrary values with SCM_TXTIME)
>
> Since loopback driver does not call (directly or indirectly)
> skb_scrub_packet(), we need to clear skb->tstamp so that
> net_timestamp_check() can eventually resample the time,
> using ktime_get_real().
>
> Fixes: 80b14dee2bea ("net: Add a new socket option for a future transmit time.")
> Fixes: fb420d5d91c1 ("tcp/fq: move back to CLOCK_MONOTONIC")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Willem de Bruijn <willemb@...gle.com>
> Cc: Soheil Hassas Yeganeh <soheil@...gle.com>

Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>

Thank you, Eric!

> ---
>  drivers/net/loopback.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c
> index a7207fa7e451311aed13cdeb100e0ea7922931bf..2df7f60fe05220c19896a251b6b15239f4b95112 100644
> --- a/drivers/net/loopback.c
> +++ b/drivers/net/loopback.c
> @@ -69,6 +69,10 @@ static netdev_tx_t loopback_xmit(struct sk_buff *skb,
>         int len;
>
>         skb_tx_timestamp(skb);
> +
> +       /* do not fool net_timestamp_check() with various clock bases */
> +       skb->tstamp = 0;
> +
>         skb_orphan(skb);
>
>         /* Before queueing this packet to netif_rx(),
> --
> 2.19.1.568.g152ad8e336-goog
>