Re: [PATCH net-next v4 2/4] net: ipv6: ioam6_iptunnel: mitigate 2-realloc issue

[Paolo Abeni <pabeni@redhat.com>]

On 11/18/24 14:15, Justin Iurman wrote:
> @@ -387,45 +392,40 @@ static int ioam6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
>  		goto drop;
>  	}
>  
> -	err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
> -	if (unlikely(err))
> -		goto drop;
> +	if (unlikely(!dst)) {
> +		struct ipv6hdr *hdr = ipv6_hdr(skb);
> +		struct flowi6 fl6;
> +
> +		memset(&fl6, 0, sizeof(fl6));
> +		fl6.daddr = hdr->daddr;
> +		fl6.saddr = hdr->saddr;
> +		fl6.flowlabel = ip6_flowinfo(hdr);
> +		fl6.flowi6_mark = skb->mark;
> +		fl6.flowi6_proto = hdr->nexthdr;
> +
> +		dst = ip6_route_output(net, NULL, &fl6);
> +		if (dst->error) {
> +			err = dst->error;
> +			dst_release(dst);
> +			goto drop;
> +		}
>  
> -	if (!ipv6_addr_equal(&orig_daddr, &ipv6_hdr(skb)->daddr)) {
>  		local_bh_disable();
> -		dst = dst_cache_get(&ilwt->cache);
> +		dst_cache_set_ip6(&ilwt->cache, dst, &fl6.saddr);
>  		local_bh_enable();
>  
> -		if (unlikely(!dst)) {
> -			struct ipv6hdr *hdr = ipv6_hdr(skb);
> -			struct flowi6 fl6;
> -
> -			memset(&fl6, 0, sizeof(fl6));
> -			fl6.daddr = hdr->daddr;
> -			fl6.saddr = hdr->saddr;
> -			fl6.flowlabel = ip6_flowinfo(hdr);
> -			fl6.flowi6_mark = skb->mark;
> -			fl6.flowi6_proto = hdr->nexthdr;
> -
> -			dst = ip6_route_output(net, NULL, &fl6);
> -			if (dst->error) {
> -				err = dst->error;
> -				dst_release(dst);
> -				goto drop;
> -			}
> -
> -			local_bh_disable();
> -			dst_cache_set_ip6(&ilwt->cache, dst, &fl6.saddr);
> -			local_bh_enable();
> -		}
> +		err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
> +		if (unlikely(err))
> +			goto drop;
> +	}
>  
> -		skb_dst_drop(skb);
> -		skb_dst_set(skb, dst);
> +	skb_dst_drop(skb);
> +	skb_dst_set(skb, dst);

Why the above 2 statements are not done only in case of ip address
match, as in the existing code?

>  
> +	if (!ipv6_addr_equal(&orig_daddr, &ipv6_hdr(skb)->daddr))
>  		return dst_output(net, sk, skb);
> -	}


Thanks,

Paolo