linux-kernel - Re: [RFC PATCH v2 net-next 14/16] net: dsa: don't set skb->offload_fwd

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Date:   Mon, 22 Mar 2021 09:06:16 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Tobias Waldekranz <tobias@...dekranz.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <nikolay@...dia.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Ido Schimmel <idosch@...sch.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        UNGLinuxDriver@...rochip.com, Vadym Kochan <vkochan@...vell.com>,
        Taras Chornyi <tchornyi@...vell.com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Ivan Vecera <ivecera@...hat.com>, linux-omap@...r.kernel.org,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [RFC PATCH v2 net-next 14/16] net: dsa: don't set
 skb->offload_fwd_mark when not offloading the bridge



On 3/18/2021 4:18 PM, Vladimir Oltean 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.
> 
> Without this change, sending a packet to the CPU for an unoffloaded
> interface triggers this WARN_ON:
> 
> void nbp_switchdev_frame_mark(const struct net_bridge_port *p,
> 			      struct sk_buff *skb)
> {
> 	if (skb->offload_fwd_mark && !WARN_ON_ONCE(!p->offload_fwd_mark))
> 		BR_INPUT_SKB_CB(skb)->offload_fwd_mark = p->offload_fwd_mark;
> }
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> Reviewed-by: Tobias Waldekranz <tobias@...dekranz.com>

Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
-- 
Florian