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SubjectRe: [PATCH net-next 1/3] net: gre_demux: add skb drop reasons to gre_rcv()
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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);

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