netdev - Re: [PATCH net-next 4/4] net/sched: act_mirred: Implement ingress actions

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Date:   Mon, 26 Sep 2016 16:43:16 +0200
From:   Hannes Frederic Sowa <hannes@...essinduktion.org>
To:     Florian Westphal <fw@...len.de>,
        Jamal Hadi Salim <jhs@...atatu.com>
Cc:     Shmulik Ladkani <shmulik.ladkani@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        WANG Cong <xiyou.wangcong@...il.com>,
        Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH net-next 4/4] net/sched: act_mirred: Implement ingress
 actions

On 26.09.2016 03:35, Florian Westphal wrote:
> Jamal Hadi Salim <jhs@...atatu.com> wrote:
>> On 16-09-25 02:31 PM, Florian Westphal wrote:
>>> Shmulik Ladkani <shmulik.ladkani@...il.com> wrote:
>>>> We can later address any loop-detection improvements in mirred.
>>>> WDYT?
>>>
>>> You can address this after fixing infamous spinlock recursion hard
>>> lockup (which has existed forever):
>>>
>>> tc qdisc add dev eth0 root handle 1: prio
>>> tc filter add dev eth0 parent 1: protocol ip u32 match u32 0 0 flowid
>>> 1:2 action mirred egress redirect dev eth0
>>>
>>> (only do this on toy vm)
>>>
>>
>> Realize didnt respond to this. Seems very simple to fix:
>> if skb->dev->ifindex and m->tcfm_dev->ifindex are the
>> same, then you can drop the packet.
> 
> Yes, but I think we get same issue when we deal with stacked
> interfaces, and redirect is to e.g. vlan on top of physical device.

We do have the adjacent upper lists in all netdevices, calculating if a
mirred actions would insert the skb on a stacked device above us should
be as easy as querying netdev_has_upper_dev and should be possible to
check that during config time.

> And we have such loops even without tc, for instance when placing
> both veth ends in same bridge :-(

We can't fix that without a ttl in the sk_buff struct.

Bye,
Hannes