netdev - Re: [PATCH net v3 3/4] udp: do not transition UDP GRO fraglist partial checksums to unnecessary

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Date: Fri, 22 Mar 2024 13:29:40 -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 v3 3/4] 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.
> 
> Fixes: 9fd1ff5d2ac7 ("udp: Support UDP fraglist GRO/GSO.")
> Signed-off-by: Antoine Tenart <atenart@...nel.org>

Sorry to have yet more questions, but

Should fraglist UDP GRO and non-fraglist (udp_gro_complete_segment)
have the same checksumming behavior?

Second, this leaves CHECKSUM_COMPLETE as is. Is that intentional? I
don't immediately see where GSO skb->csum would be updated.

I can take a closer look too, but did not want to delay feedback.

> ---
>  net/ipv4/udp_offload.c | 8 +-------
>  net/ipv6/udp_offload.c | 8 +-------
>  2 files changed, 2 insertions(+), 14 deletions(-)
> 
> diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
> index 3bb69464930b..548476d78237 100644
> --- a/net/ipv4/udp_offload.c
> +++ b/net/ipv4/udp_offload.c
> @@ -722,13 +722,7 @@ INDIRECT_CALLABLE_SCOPE int udp4_gro_complete(struct sk_buff *skb, int nhoff)
>  		skb_shinfo(skb)->gso_type |= (SKB_GSO_FRAGLIST|SKB_GSO_UDP_L4);
>  		skb_shinfo(skb)->gso_segs = NAPI_GRO_CB(skb)->count;
>  
> -		if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
> -			if (skb->csum_level < SKB_MAX_CSUM_LEVEL)
> -				skb->csum_level++;
> -		} else {
> -			skb->ip_summed = CHECKSUM_UNNECESSARY;
> -			skb->csum_level = 0;
> -		}
> +		__skb_incr_checksum_unnecessary(skb);
>  
>  		return 0;
>  	}
> diff --git a/net/ipv6/udp_offload.c b/net/ipv6/udp_offload.c
> index 312bcaeea96f..bbd347de00b4 100644
> --- a/net/ipv6/udp_offload.c
> +++ b/net/ipv6/udp_offload.c
> @@ -174,13 +174,7 @@ INDIRECT_CALLABLE_SCOPE int udp6_gro_complete(struct sk_buff *skb, int nhoff)
>  		skb_shinfo(skb)->gso_type |= (SKB_GSO_FRAGLIST|SKB_GSO_UDP_L4);
>  		skb_shinfo(skb)->gso_segs = NAPI_GRO_CB(skb)->count;
>  
> -		if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
> -			if (skb->csum_level < SKB_MAX_CSUM_LEVEL)
> -				skb->csum_level++;
> -		} else {
> -			skb->ip_summed = CHECKSUM_UNNECESSARY;
> -			skb->csum_level = 0;
> -		}
> +		__skb_incr_checksum_unnecessary(skb);
>  
>  		return 0;
>  	}
> -- 
> 2.44.0
>