Re: [RFC PATCH v2 net-next 14/16] net: dsa: don't set skb->offload_fwd_mark when not offloading the bridge

[Florian Fainelli <f.fainelli@gmail.com>]

On 3/18/2021 4:18 PM, Vladimir Oltean 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.
> 
> 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@nxp.com>
> Reviewed-by: Tobias Waldekranz <tobias@waldekranz.com>

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