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Date:   Tue, 15 Mar 2022 21:49:01 -0600
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Subject: Re: [PATCH net-next 1/3] net: gre_demux: add skb drop reasons to
 gre_rcv()
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To:     Jakub Kicinski <kuba@kernel.org>, menglong8.dong@gmail.com
Cc:     rostedt@goodmis.org, mingo@redhat.com, xeb@mail.ru,
        davem@davemloft.net, yoshfuji@linux-ipv6.org,
        imagedong@tencent.com, edumazet@google.com, kafai@fb.com,
        talalahmad@google.com, keescook@chromium.org, alobakin@pm.me,
        flyingpeng@tencent.com, mengensun@tencent.com,
        dongli.zhang@oracle.com, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, Biao Jiang <benbjiang@tencent.com>
References: <20220314133312.336653-1-imagedong@tencent.com>
 <20220314133312.336653-2-imagedong@tencent.com>
 <20220315200847.68c2efee@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
From:   David Ahern <dsahern@kernel.org>
In-Reply-To: <20220315200847.68c2efee@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
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On 3/15/22 9:08 PM, Jakub Kicinski wrote:
> On Mon, 14 Mar 2022 21:33:10 +0800 menglong8.dong@gmail.com wrote:
>> +	reason = SKB_DROP_REASON_NOT_SPECIFIED;
>>  	if (!pskb_may_pull(skb, 12))
>>  		goto drop;
> 
> REASON_HDR_TRUNC ?
> 
>>  	ver = skb->data[1]&0x7f;
>> -	if (ver >= GREPROTO_MAX)
>> +	if (ver >= GREPROTO_MAX) {
>> +		reason = SKB_DROP_REASON_GRE_VERSION;
> 
> TBH I'm still not sure what level of granularity we should be shooting
> for with the reasons. I'd throw all unexpected header values into one 
> bucket, not go for a reason per field, per protocol. But as I'm said
> I'm not sure myself, so we can keep what you have..

I have stated before I do not believe every single drop point in the
kernel needs a unique reason code. This is overkill. The reason augments
information we already have -- the IP from kfree_skb tracepoint.

> 
>>  		goto drop;
>> +	}
>>  
>>  	rcu_read_lock();
>>  	proto = rcu_dereference(gre_proto[ver]);
>> -	if (!proto || !proto->handler)
>> +	if (!proto || !proto->handler) {
>> +		reason = SKB_DROP_REASON_GRE_NOHANDLER;
> 
> I think the ->handler check is defensive programming, there's no
> protocol upstream which would leave handler NULL.
> 
> This is akin to SKB_DROP_REASON_PTYPE_ABSENT, we can reuse that or add
> a new reason, but I'd think the phrasing should be kept similar.
> 
>>  		goto drop_unlock;
>> +	}
>>  	ret = proto->handler(skb);