netdev - Re: [PATCH net-next v3 3/3] net: icmp: add reasons of the skb drops to icmp protocol

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Message-ID: <20220316201853.0734280f@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Wed, 16 Mar 2022 20:18:53 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     menglong8.dong@...il.com, dsahern@...nel.org
Cc:     pabeni@...hat.com, rostedt@...dmis.org, mingo@...hat.com,
        xeb@...l.ru, davem@...emloft.net, yoshfuji@...ux-ipv6.org,
        imagedong@...cent.com, edumazet@...gle.com, kafai@...com,
        talalahmad@...gle.com, keescook@...omium.org, alobakin@...me,
        flyingpeng@...cent.com, mengensun@...cent.com,
        dongli.zhang@...cle.com, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, benbjiang@...cent.com
Subject: Re: [PATCH net-next v3 3/3] net: icmp: add reasons of the skb drops
 to icmp protocol

On Wed, 16 Mar 2022 14:31:48 +0800 menglong8.dong@...il.com wrote:
> From: Menglong Dong <imagedong@...cent.com>
> 
> Replace kfree_skb() used in icmp_rcv() and icmpv6_rcv() with
> kfree_skb_reason().
> 
> In order to get the reasons of the skb drops after icmp message handle,
> we change the return type of 'handler()' in 'struct icmp_control' from
> 'bool' to 'enum skb_drop_reason'. This may change its original
> intention, as 'false' means failure, but 'SKB_NOT_DROPPED_YET' means
> success now. Therefore, all 'handler' and the call of them need to be
> handled. Following 'handler' functions are involved:
> 
> icmp_unreach()
> icmp_redirect()
> icmp_echo()
> icmp_timestamp()
> icmp_discard()
> 
> And following new drop reasons are added:
> 
> SKB_DROP_REASON_ICMP_CSUM
> SKB_DROP_REASON_ICMP_TYPE
> SKB_DROP_REASON_ICMP_BROADCAST
> 
> Reviewed-by: Hao Peng <flyingpeng@...cent.com>
> Reviewed-by: Jiang Biao <benbjiang@...cent.com>
> Signed-off-by: Menglong Dong <imagedong@...cent.com>

I guess this set raises the follow up question to Dave if adding 
drop reasons to places with MIB exception stats means improving 
the granularity or one MIB stat == one reason?

> -bool ping_rcv(struct sk_buff *skb)
> +enum skb_drop_reason ping_rcv(struct sk_buff *skb)
>  {
> +	enum skb_drop_reason reason = SKB_DROP_REASON_NO_SOCKET;
>  	struct sock *sk;
>  	struct net *net = dev_net(skb->dev);
>  	struct icmphdr *icmph = icmp_hdr(skb);
> -	bool rc = false;
>  
>  	/* We assume the packet has already been checked by icmp_rcv */
>  
> @@ -980,15 +980,17 @@ bool ping_rcv(struct sk_buff *skb)
>  		struct sk_buff *skb2 = skb_clone(skb, GFP_ATOMIC);
>  
>  		pr_debug("rcv on socket %p\n", sk);
> -		if (skb2 && !ping_queue_rcv_skb(sk, skb2))
> -			rc = true;
> +		if (skb2)
> +			reason = __ping_queue_rcv_skb(sk, skb2);
> +		else
> +			reason = SKB_DROP_REASON_NOMEM;
>  		sock_put(sk);
>  	}
>  
> -	if (!rc)
> +	if (reason)
>  		pr_debug("no socket, dropping\n");

This is going to be printed on memory allocation failures now as well.