Subject: Re: [PATCH] net: take care of bonding in build_skb_flow_key (v3)

From: zhuyj <[email-masked]>
Date: Wed, 20 Jan 2016 14:32:05 +0800

On 01/20/2016 02:29 PM, zhuyj wrote:
> On 01/20/2016 02:24 PM, zhuyj wrote:
>> 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 <[email-masked]>
>>> ---
>>>   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?
>> That is, rtnl_lock is called frequently. Maybe other functions have 
>> little chance to call rtnl_lock.
>
> Maybe this function netdev_master_upper_dev_get_rcu is better? I am 
> not sure.

Maybe this function netdev_master_upper_dev_get_rcu is better? I am not 
sure.

>
>>
>> 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);
>>>   }
>>
>