netdev - Re: [PATCH net-next 4/4] net: dsa: don't set skb->offload_fwd

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Date:   Mon, 15 Feb 2021 09:48:38 -0600
From:   George McCollister <george.mccollister@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Woojung Huh <woojung.huh@...rochip.com>,
        UNGLinuxDriver@...rochip.com, Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Tobias Waldekranz <tobias@...dekranz.com>,
        DENG Qingfang <dqfext@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
        Oleksij Rempel <linux@...pel-privat.de>
Subject: Re: [PATCH net-next 4/4] net: dsa: don't set skb->offload_fwd_mark
 when not offloading the bridge

On Sun, Feb 14, 2021 at 9:54 AM Vladimir Oltean <olteanv@...il.com> wrote:
[snip]
> diff --git a/net/dsa/tag_xrs700x.c b/net/dsa/tag_xrs700x.c
> index 858cdf9d2913..215ecceea89e 100644
> --- a/net/dsa/tag_xrs700x.c
> +++ b/net/dsa/tag_xrs700x.c
> @@ -45,8 +45,7 @@ static struct sk_buff *xrs700x_rcv(struct sk_buff *skb, struct net_device *dev,
>         if (pskb_trim_rcsum(skb, skb->len - 1))
>                 return NULL;
>
> -       /* Frame is forwarded by hardware, don't forward in software. */
> -       skb->offload_fwd_mark = 1;
> +       dsa_default_offload_fwd_mark(skb);

Does it make sense that the following would have worked prior to this
change? Is this only an issue for bridging between DSA ports when
offloading is supported? lan0 is a port an an xrs700x switch:

ip link set eth0 up
ip link del veth0
ip link add veth0 type veth peer name veth1

for eth in veth0 veth1 lan1; do
    ip link set ${eth} up
done
ip link add br0 type bridge
ip link set veth1 master br0
ip link set lan1 master br0
ip link set br0 up

ip addr add 192.168.2.1/24 dev veth0

# ping host connected to physical LAN that lan0 is on
ping 192.168.2.249 (works!)

I was trying to come up with a way to test this change and expected
this would fail (and your patch) would fix it based on what you're
described.

-George

>
>         return skb;
>  }
> --
> 2.25.1
>