netdev - Re: [PATCH net] net: sched: act_mirred: drop skb's dst

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Date:   Mon, 14 Oct 2019 15:08:54 +0800
From:   Zhiyuan Hou <zhiyuan2048@...ux.alibaba.com>
To:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        "David S . Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: sched: act_mirred: drop skb's dst_entry in
 ingress redirection


On 2019/10/13 3:34 上午, Sergei Shtylyov wrote:
> Hello!
>
> On 10/12/2019 10:16 AM, Zhiyuan Hou wrote:
>
>> In act_mirred's ingress redirection, if the skb's dst_entry is valid
>> when call function netif_receive_skb, the fllowing l3 stack process
>    Following or flowing?
Sorry, it should be following. I will change it in next version.
>> (ip_rcv_finish_core) will check dst_entry and skip the routing
>> decision. Using the old dst_entry is unexpected and may discard the
>> skb in some case. For example dst->dst_input points to dst_discard.
>>
>> This patch drops the skb's dst_entry before calling netif_receive_skb
>> so that the skb can be made routing decision like a normal ingress
>> skb.
>>
>> Signed-off-by: Zhiyuan Hou<zhiyuan2048@...ux.alibaba.com>
>> ---
>>   net/sched/act_mirred.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c
>> index 9ce073a05414..6108a64c0cd5 100644
>> --- a/net/sched/act_mirred.c
>> +++ b/net/sched/act_mirred.c
> [...]
>> @@ -298,8 +299,10 @@ static int tcf_mirred_act(struct sk_buff *skb, const struct tc_action *a,
>>   
>>   	if (!want_ingress)
>>   		err = dev_queue_xmit(skb2);
>> -	else
>> +	else {
>> +		skb_dst_drop(skb2);
>>   		err = netif_receive_skb(skb2);
>> +	}
>     If you introduce {} in one *if* branch, {} should be added to the other branches as well,
> says CodingStyle.
I will change it in next version . Thanks.
> [...]
>
> MBR, Sergei