netdev - RE: [Patch bpf v3 8/8] skmsg: increase sk->sk

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Date:   Thu, 27 May 2021 22:27:37 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org
Cc:     bpf@...r.kernel.org, Cong Wang <cong.wang@...edance.com>,
        John Fastabend <john.fastabend@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Lorenz Bauer <lmb@...udflare.com>
Subject: RE: [Patch bpf v3 8/8] skmsg: increase sk->sk_drops when dropping
 packets

Cong Wang wrote:
> From: Cong Wang <cong.wang@...edance.com>
> 
> It is hard to observe packet drops without increasing relevant
> drop counters, here we should increase sk->sk_drops which is
> a protocol-independent counter. Fortunately psock is always
> associated with a struct sock, we can just use psock->sk.
> 
> Suggested-by: John Fastabend <john.fastabend@...il.com>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Jakub Sitnicki <jakub@...udflare.com>
> Cc: Lorenz Bauer <lmb@...udflare.com>
> Signed-off-by: Cong Wang <cong.wang@...edance.com>
> ---
>  net/core/skmsg.c | 22 ++++++++++++++--------
>  1 file changed, 14 insertions(+), 8 deletions(-)
> 

[...]

> @@ -942,7 +948,7 @@ static int sk_psock_verdict_apply(struct sk_psock *psock, struct sk_buff *skb,
>  	case __SK_DROP:
>  	default:
>  out_free:
> -		kfree_skb(skb);
> +		sock_drop(psock->sk, skb);

I must have missed this on first review.

Why should we mark a packet we intentionally drop as sk_drops? I think
we should leave it as just kfree_skb() this way sk_drops is just
the error cases and if users want this counter they can always add
it to the bpf prog itself.

>  	}
>  
>  	return err;