netdev - Re: [PATCH] net: take care of bonding in build_skb_flow

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Date:	Wed, 20 Jan 2016 17:47:11 +0800
From:	Wengang Wang <wen.gang.wang@...cle.com>
To:	zhuyj <zyjzyj2000@...il.com>, netdev@...r.kernel.org
Cc:	jay.vosburgh@...onical.com
Subject: Re: [PATCH] net: take care of bonding in build_skb_flow_key (v3)



在 2016年01月20日 15:54, zhuyj 写道:
> On 01/20/2016 03:38 PM, Wengang Wang wrote:
>>
>>
>> 在 2016年01月20日 14:24, zhuyj 写道:
>>> On 01/20/2016 01:32 PM, Wengang Wang wrote:
>>>> In a bonding setting, we determines fragment size according to MTU and
>>>> PMTU associated to the bonding master. If the slave finds the fragment
>>>> size is too big, it drops the fragment and calls ip_rt_update_pmtu(),
>>>> passing _skb_ and _pmtu_, trying to update the path MTU.
>>>> Problem is that the target device that function ip_rt_update_pmtu 
>>>> actually
>>>> tries to update is the slave (skb->dev), not the master. Thus since no
>>>> PMTU change happens on master, the fragment size for later packets 
>>>> doesn't
>>>> change so all later fragments/packets are dropped too.
>>>>
>>>> The fix is letting build_skb_flow_key() take care of the transition of
>>>> device index from bonding slave to the master. That makes the 
>>>> master become
>>>> the target device that ip_rt_update_pmtu tries to update PMTU to.
>>>>
>>>> Signed-off-by: Wengang Wang <wen.gang.wang@...cle.com>
>>>> ---
>>>>   net/ipv4/route.c | 13 ++++++++++++-
>>>>   1 file changed, 12 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
>>>> index 85f184e..c59fb0d 100644
>>>> --- a/net/ipv4/route.c
>>>> +++ b/net/ipv4/route.c
>>>> @@ -523,10 +523,21 @@ static void build_skb_flow_key(struct flowi4 
>>>> *fl4, const struct sk_buff *skb,
>>>>                      const struct sock *sk)
>>>>   {
>>>>       const struct iphdr *iph = ip_hdr(skb);
>>>> -    int oif = skb->dev->ifindex;
>>>> +    struct net_device *master = NULL;
>>>>       u8 tos = RT_TOS(iph->tos);
>>>>       u8 prot = iph->protocol;
>>>>       u32 mark = skb->mark;
>>>> +    int oif;
>>>> +
>>>> +    if (skb->dev->flags & IFF_SLAVE) {
>>>> +        rtnl_lock();
>>>> +        master = netdev_master_upper_dev_get(skb->dev);
>>>> +        rtnl_unlock();
>>> update_pmtu is called very frequently. Is it appropriate to use 
>>> rtnl_lock here?
>> By "very frequently", how frequently it is expected? And what 
>> situation can cause that?
>> For my case, the update_pmtu is called only once.
> ip_tunnel_xmit
>
Can you please explain with more details?

thanks,
wengang


> Zhu Yanjun
>
>>
>> thanks,
>> wengang
>>
>>> That is, rtnl_lock is called frequently. Maybe other functions have 
>>> little chance to call rtnl_lock.
>>>
>>> Best Regards!
>>> Zhu Yanjun
>>>> +    }
>>>> +    if (master)
>>>> +        oif = master->ifindex;
>>>> +    else
>>>> +        oif = skb->dev->ifindex;
>>>>         __build_flow_key(fl4, sk, iph, oif, tos, prot, mark, 0);
>>>>   }
>>>
>>
>