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

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Date:   Fri, 26 Feb 2021 20:14:30 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Tobias Waldekranz <tobias@...dekranz.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>,
        George McCollister <george.mccollister@...il.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 Thu, Feb 25, 2021 at 08:25:23PM +0100, Tobias Waldekranz wrote:
> On Sun, Feb 14, 2021 at 17:53, Vladimir Oltean <olteanv@...il.com> wrote:
> > From: Vladimir Oltean <vladimir.oltean@....com>
> >
> > DSA has gained the recent ability to deal gracefully with upper
> > interfaces it cannot offload, such as the bridge, bonding or team
> > drivers. When such uppers exist, the ports are still in standalone mode
> > as far as the hardware is concerned.
> >
> > But when we deliver packets to the software bridge in order for that to
> > do the forwarding, there is an unpleasant surprise in that the bridge
> > will refuse to forward them. This is because we unconditionally set
> > skb->offload_fwd_mark = true, meaning that the bridge thinks the frames
> > were already forwarded in hardware by us.
> >
> > Since dp->bridge_dev is populated only when there is hardware offload
> > for it, but not in the software fallback case, let's introduce a new
> > helper that can be called from the tagger data path which sets the
> > skb->offload_fwd_mark accordingly to zero when there is no hardware
> > offload for bridging. This lets the bridge forward packets back to other
> > interfaces of our switch, if needed.
> >
> > Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> > ---
> 
> For the generic and tag_dsa.c related changes:
> 
> Reviewed-by: Tobias Waldekranz <tobias@...dekranz.com>

Actually with my switchdev_bridge_port_offload_notify() proposal, I
don't think this patch is going to be needed at all. I think the bridge
happily ignores a packet with skb->offload_fwd_mark = 1 if it comes from
a port which has an offload_fwd_mark of 0, although I haven't tested that.