netdev - Re: [PATCH net-next] net l2tp: drop flow hash on forward

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Date: Sat, 20 Apr 2024 15:02:57 +0100
From: Daniel Golle <daniel@...rotopia.org>
To: David Bauer <mail@...id-bauer.net>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net l2tp: drop flow hash on forward

On Sat, Apr 20, 2024 at 03:39:40PM +0200, David Bauer wrote:
> Drop the flow-hash of the skb when forwarding to the L2TP netdev.
> 
> This avoids the L2TP qdisc from using the flow-hash from the outer
> packet, which is identical for every flow within the tunnel.
> 
> This does not affect every platform but is specific for the ethernet
> driver. It depends on the platform including L4 information in the
> flow-hash.
> 
> One such example is the Mediatek Filogic MT798x family of networking
> processors.
> 
> Signed-off-by: David Bauer <mail@...id-bauer.net>

While it's difficult to say which exact commit this fixes, I still
consider it being a fix, as otherwise flow-offloading on mentioned
platforms will face difficulties when using L2TP (right?).
Hence maybe it should go via 'net' tree rather than via 'net-next'?

The fix itself looks fine to me.

> ---
>  net/l2tp/l2tp_eth.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/l2tp/l2tp_eth.c b/net/l2tp/l2tp_eth.c
> index 39e487ccc468..8ba00ad433c2 100644
> --- a/net/l2tp/l2tp_eth.c
> +++ b/net/l2tp/l2tp_eth.c
> @@ -127,6 +127,9 @@ static void l2tp_eth_dev_recv(struct l2tp_session *session, struct sk_buff *skb,
>  	/* checksums verified by L2TP */
>  	skb->ip_summed = CHECKSUM_NONE;
>  
> +	/* drop outer flow-hash */
> +	skb_clear_hash(skb);
> +
>  	skb_dst_drop(skb);
>  	nf_reset_ct(skb);
>  
> -- 
> 2.43.0
> 
>