netdev - Re: [PATCH net v2 3/4] udp: do not transition UDP fraglist to unnecessary checksum

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Date: Tue, 19 Mar 2024 09:38:20 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Antoine Tenart <atenart@...nel.org>, 
 davem@...emloft.net, 
 kuba@...nel.org, 
 pabeni@...hat.com, 
 edumazet@...gle.com
Cc: Antoine Tenart <atenart@...nel.org>, 
 steffen.klassert@...unet.com, 
 willemdebruijn.kernel@...il.com, 
 netdev@...r.kernel.org
Subject: Re: [PATCH net v2 3/4] udp: do not transition UDP fraglist to
 unnecessary checksum

Antoine Tenart wrote:
> udp4/6_gro_complete transition fraglist packets to CHECKSUM_UNNECESSARY
> and sets their checksum level based on if the packet is recognized to be
> a tunneled one. However there is no safe way to detect a packet is a
> tunneled one and in case such packet is GROed at the UDP level, setting
> a wrong checksum level will lead to later errors. For example if those
> packets are forwarded to the Tx path they could produce the following
> dump:
> 
>   gen01: hw csum failure
>   skb len=3008 headroom=160 headlen=1376 tailroom=0
>   mac=(106,14) net=(120,40) trans=160
>   shinfo(txflags=0 nr_frags=0 gso(size=0 type=0 segs=0))
>   csum(0xffff232e ip_summed=2 complete_sw=0 valid=0 level=0)
>   hash(0x77e3d716 sw=1 l4=1) proto=0x86dd pkttype=0 iif=12
>   ...
> 
> Fixes: 9fd1ff5d2ac7 ("udp: Support UDP fraglist GRO/GSO.")
> Signed-off-by: Antoine Tenart <atenart@...nel.org>

The original patch converted to CHECKSUM_UNNECESSARY for a reason.
The skb->csum of the main gso_skb is not valid?

Should instead only the csum_level be adjusted, to always keep
csum_level == 0?