Re: [PATCH net-next v4 2/5] net: gro: only merge packets with incrementing or fixed outer ids

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Richard Gobert wrote:
> Only merge encapsulated packets if their outer IDs are either
> incrementing or fixed, just like for inner IDs and IDs of non-encapsulated
> packets.
> 
> Add another ip_fixedid bit for a total of two bits: one for outer IDs (and
> for unencapsulated packets) and one for inner IDs.
> 
> This commit preserves the current behavior of GSO where only the IDs of the
> inner-most headers are restored correctly.
> 
> Signed-off-by: Richard Gobert <richardbgobert@gmail.com>
> ---
>  include/net/gro.h      | 30 +++++++++++++++---------------
>  net/ipv4/tcp_offload.c |  5 ++++-
>  2 files changed, 19 insertions(+), 16 deletions(-)
> 
> diff --git a/include/net/gro.h b/include/net/gro.h
> index 87c68007f949..322c5517f508 100644
> --- a/include/net/gro.h
> +++ b/include/net/gro.h
> @@ -75,7 +75,7 @@ struct napi_gro_cb {
>  		u8	is_fou:1;
>  
>  		/* Used to determine if ipid_offset can be ignored */
> -		u8	ip_fixedid:1;
> +		u8	ip_fixedid:2;
>  
>  		/* Number of gro_receive callbacks this packet already went through */
>  		u8 recursion_counter:4;
> @@ -442,29 +442,26 @@ static inline __wsum ip6_gro_compute_pseudo(const struct sk_buff *skb,
>  }
>  
>  static inline int inet_gro_flush(const struct iphdr *iph, const struct iphdr *iph2,
> -				 struct sk_buff *p, bool outer)
> +				 struct sk_buff *p, bool inner)
>  {
>  	const u32 id = ntohl(*(__be32 *)&iph->id);
>  	const u32 id2 = ntohl(*(__be32 *)&iph2->id);
>  	const u16 ipid_offset = (id >> 16) - (id2 >> 16);
>  	const u16 count = NAPI_GRO_CB(p)->count;
>  	const u32 df = id & IP_DF;
> -	int flush;
>  
>  	/* All fields must match except length and checksum. */
> -	flush = (iph->ttl ^ iph2->ttl) | (iph->tos ^ iph2->tos) | (df ^ (id2 & IP_DF));
> -
> -	if (flush | (outer && df))
> -		return flush;
> +	if ((iph->ttl ^ iph2->ttl) | (iph->tos ^ iph2->tos) | (df ^ (id2 & IP_DF)))
> +		return true;
>  
>  	/* When we receive our second frame we can make a decision on if we
>  	 * continue this flow as an atomic flow with a fixed ID or if we use
>  	 * an incrementing ID.
>  	 */
>  	if (count == 1 && df && !ipid_offset)
> -		NAPI_GRO_CB(p)->ip_fixedid = true;
> +		NAPI_GRO_CB(p)->ip_fixedid |= 1 << inner;
>  
> -	return ipid_offset ^ (count * !NAPI_GRO_CB(p)->ip_fixedid);
> +	return ipid_offset ^ (count * !(NAPI_GRO_CB(p)->ip_fixedid & (1 << inner)));
>  }
>  
>  static inline int ipv6_gro_flush(const struct ipv6hdr *iph, const struct ipv6hdr *iph2)
> @@ -479,7 +476,7 @@ static inline int ipv6_gro_flush(const struct ipv6hdr *iph, const struct ipv6hdr
>  
>  static inline int __gro_receive_network_flush(const void *th, const void *th2,
>  					      struct sk_buff *p, const u16 diff,
> -					      bool outer)
> +					      bool inner)
>  {
>  	const void *nh = th - diff;
>  	const void *nh2 = th2 - diff;
> @@ -487,19 +484,22 @@ static inline int __gro_receive_network_flush(const void *th, const void *th2,
>  	if (((struct iphdr *)nh)->version == 6)
>  		return ipv6_gro_flush(nh, nh2);
>  	else
> -		return inet_gro_flush(nh, nh2, p, outer);
> +		return inet_gro_flush(nh, nh2, p, inner);
>  }
>  
>  static inline int gro_receive_network_flush(const void *th, const void *th2,
>  					    struct sk_buff *p)
>  {
> -	const bool encap_mark = NAPI_GRO_CB(p)->encap_mark;
>  	int off = skb_transport_offset(p);
>  	int flush;
> +	int diff;
>  
> -	flush = __gro_receive_network_flush(th, th2, p, off - NAPI_GRO_CB(p)->network_offset, encap_mark);
> -	if (encap_mark)
> -		flush |= __gro_receive_network_flush(th, th2, p, off - NAPI_GRO_CB(p)->inner_network_offset, false);
> +	diff = off - NAPI_GRO_CB(p)->network_offset;
> +	flush = __gro_receive_network_flush(th, th2, p, diff, false);
> +	if (NAPI_GRO_CB(p)->encap_mark) {
> +		diff = off - NAPI_GRO_CB(p)->inner_network_offset;
> +		flush |= __gro_receive_network_flush(th, th2, p, diff, true);
> +	}

nit: this diff introduction is not needed. The patch is easier to
parse without the change. Even if line length will (still) be longer.

>  
>  	return flush;
>  }
> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
> index e6612bd84d09..1949eede9ec9 100644
> --- a/net/ipv4/tcp_offload.c
> +++ b/net/ipv4/tcp_offload.c
> @@ -471,6 +471,7 @@ INDIRECT_CALLABLE_SCOPE int tcp4_gro_complete(struct sk_buff *skb, int thoff)
>  	const u16 offset = NAPI_GRO_CB(skb)->network_offsets[skb->encapsulation];
>  	const struct iphdr *iph = (struct iphdr *)(skb->data + offset);
>  	struct tcphdr *th = tcp_hdr(skb);
> +	bool is_fixedid;
>  
>  	if (unlikely(NAPI_GRO_CB(skb)->is_flist)) {
>  		skb_shinfo(skb)->gso_type |= SKB_GSO_FRAGLIST | SKB_GSO_TCPV4;
> @@ -484,8 +485,10 @@ INDIRECT_CALLABLE_SCOPE int tcp4_gro_complete(struct sk_buff *skb, int thoff)
>  	th->check = ~tcp_v4_check(skb->len - thoff, iph->saddr,
>  				  iph->daddr, 0);
>  
> +	is_fixedid = (NAPI_GRO_CB(skb)->ip_fixedid >> skb->encapsulation) & 1;
> +
>  	skb_shinfo(skb)->gso_type |= SKB_GSO_TCPV4 |
> -			(NAPI_GRO_CB(skb)->ip_fixedid * SKB_GSO_TCP_FIXEDID);
> +			(is_fixedid * SKB_GSO_TCP_FIXEDID);

Similar to how gro_receive_network_flush is called from both transport
layers, TCP and UDP, this is needed in udp_gro_complete_segment too?

Existing equivalent block is entirely missing there.

The deeper issue is that this is named TCP_FIXEDID, but in reality it
is IPV4_FIXEDID and applies to all transport layer protocols on top.

Perhaps not to fix in this series. But a limitation of USO in the
meantime.

>  
>  	tcp_gro_complete(skb);
>  	return 0;
> -- 
> 2.36.1
>