netdev - Re: [PATCH net] skbuff: Release nfct refcount on napi stolen or re-used skbs

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Date:   Tue, 25 May 2021 15:45:02 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Paul Blakey <paulb@...dia.com>, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Oz Shlomo <ozsh@...dia.com>, Roi Dayan <roid@...dia.com>,
        Vlad Buslov <vladbu@...dia.com>
Subject: Re: [PATCH net] skbuff: Release nfct refcount on napi stolen or
 re-used skbs



On 5/25/21 11:13 AM, Paul Blakey wrote:
> When multiple SKBs are merged to a new skb under napi GRO,
> or SKB is re-used by napi, if nfct was set for them in the
> driver, it will not be released while freeing their stolen
> head state or on re-use.
> 
> Release nfct on napi's stolen or re-used SKBs.
> 
> Fixes: 5c6b94604744 ("net/mlx5e: CT: Handle misses after executing CT action")
> Reviewed-by: Roi Dayan <roid@...dia.com>
> Signed-off-by: Paul Blakey <paulb@...dia.com>
> ---
>  net/core/dev.c    | 1 +
>  net/core/skbuff.c | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index ef8cf7619baf..a5324ca7dc65 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -6243,6 +6243,7 @@ static void napi_reuse_skb(struct napi_struct *napi, struct sk_buff *skb)
>  	skb_shinfo(skb)->gso_type = 0;
>  	skb->truesize = SKB_TRUESIZE(skb_end_offset(skb));
>  	skb_ext_reset(skb);
> +	nf_reset_ct(skb);
>  
>  	napi->skb = skb;
>  }
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 3ad22870298c..6127bab2fe2f 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -939,6 +939,7 @@ void __kfree_skb_defer(struct sk_buff *skb)
>  
>  void napi_skb_free_stolen_head(struct sk_buff *skb)
>  {
> +	nf_conntrack_put(skb_nfct(skb));
>  	skb_dst_drop(skb);
>  	skb_ext_put(skb);
>  	napi_skb_cache_put(skb);
> 

Sadly we are very consistently making GRO slow as hell.

Why merging SKB with different ct would be allowed ?

If we accept this patch, then you will likely add another check in gro_list_prepare() ?