Re: [PATCH net-next 4/4] net: dsa: don't set skb->offload_fwd_mark when not offloading the bridge

From: Vladimir Oltean <olteanv@gmail.com>
To: Tobias Waldekranz <tobias@waldekranz.com>
Cc: "David S . Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	netdev@vger.kernel.org, Florian Fainelli <f.fainelli@gmail.com>,
	Andrew Lunn <andrew@lunn.ch>,
	Vivien Didelot <vivien.didelot@gmail.com>,
	Kurt Kanzenbach <kurt@linutronix.de>,
	Woojung Huh <woojung.huh@microchip.com>,
	UNGLinuxDriver@microchip.com, Sean Wang <sean.wang@mediatek.com>,
	Landen Chao <Landen.Chao@mediatek.com>,
	Claudiu Manoil <claudiu.manoil@nxp.com>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
	George McCollister <george.mccollister@gmail.com>,
	DENG Qingfang <dqfext@gmail.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	Hauke Mehrtens <hauke@hauke-m.de>,
	Rasmus Villemoes <rasmus.villemoes@prevas.dk>,
	Oleksij Rempel <linux@rempel-privat.de>
Subject: Re: [PATCH net-next 4/4] net: dsa: don't set skb->offload_fwd_mark when not offloading the bridge
Date: Fri, 26 Feb 2021 20:14:30 +0200	[thread overview]
Message-ID: <20210226181430.5q3olzmozpqpl2fm@skbuf> (raw)
In-Reply-To: <875z2grluk.fsf@waldekranz.com>

On Thu, Feb 25, 2021 at 08:25:23PM +0100, Tobias Waldekranz wrote:
> On Sun, Feb 14, 2021 at 17:53, Vladimir Oltean <olteanv@gmail.com> wrote:
> > From: Vladimir Oltean <vladimir.oltean@nxp.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@nxp.com>
> > ---
> 
> For the generic and tag_dsa.c related changes:
> 
> Reviewed-by: Tobias Waldekranz <tobias@waldekranz.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.