netdev - Re: [PATCH net] net/sched: act_ct: fix restore the qdisc_skb

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Date:   Sun, 19 Jul 2020 09:31:36 +0800
From:   wenxu <wenxu@...oud.cn>
To:     Florian Westphal <fw@...len.de>
Cc:     xiyou.wangcong@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH net] net/sched: act_ct: fix restore the qdisc_skb_cb after
 defrag


在 2020/7/18 20:30, Florian Westphal 写道:
> wenxu@...oud.cn <wenxu@...oud.cn> wrote:
>> From: wenxu <wenxu@...oud.cn>
>>
>> The fragment packets do defrag in tcf_ct_handle_fragments
>> will clear the skb->cb which make the qdisc_skb_cb clear
>> too. So the qdsic_skb_cb should be store before defrag and
>> restore after that.
>> It also update the pkt_len after all the
>> fragments finish the defrag to one packet and make the
>> following actions counter correct.
>>
>> Fixes: b57dc7c13ea9 ("net/sched: Introduce action ct")
>> Signed-off-by: wenxu <wenxu@...oud.cn>
> Looks ok to me.  One question:
>
>> @@ -1014,6 +1017,7 @@ static int tcf_ct_act(struct sk_buff *skb, const struct tc_action *a,
>>  
>>  out:
>>  	tcf_action_update_bstats(&c->common, skb);
>> +	qdisc_skb_cb(skb)->pkt_len = skb->len;
>>  	return retval;
> This appears to be unconditional, I would have expected that
> this only done for reassembled skbs?
Yes.
>
> Otherwise we will lose the value calculated by core via
> qdisc_calculate_pkt_len().

qdisc_calculate_pkt_len only be cablled in dev_xmit_skb and qdisc_enqueue. If all the fragment will

pass those before defrag, it will caculate correctly. If the reassembled packets pass those, it also caculate correctly after we recaculate the pkt_len of qdisc_skb_cb