netdev - Re: [PATCH net v4 3/5] udp: do not transition UDP GRO fraglist partial checksums to unnecessary

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Message-ID: <6602cfd748870_13d9ab2942e@willemb.c.googlers.com.notmuch>
Date: Tue, 26 Mar 2024 09:38:31 -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 v4 3/5] udp: do not transition UDP GRO fraglist
 partial checksums to unnecessary

Antoine Tenart wrote:
> UDP GRO validates checksums and in udp4/6_gro_complete fraglist packets
> are converted to CHECKSUM_UNNECESSARY to avoid later checks. However
> this is an issue for CHECKSUM_PARTIAL packets as they can be looped in
> an egress path and then their partial checksums are not fixed.
> 
> Different issues can be observed, from invalid checksum on packets to
> traces like:
> 
>   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
>   ...
> 
> Fix this by only converting CHECKSUM_NONE packets to
> CHECKSUM_UNNECESSARY by reusing __skb_incr_checksum_unnecessary. All
> other checksum types are kept as-is, including CHECKSUM_COMPLETE as
> fraglist packets being segmented back would have their skb->csum valid.
> 
> Fixes: 9fd1ff5d2ac7 ("udp: Support UDP fraglist GRO/GSO.")
> Signed-off-by: Antoine Tenart <atenart@...nel.org>

Reviewed-by: Willem de Bruijn <willemb@...gle.com>