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

From: Wengang Wang <[email-masked]>
Date: Thu, 21 Jan 2016 10:40:34 +0800

在 2016年01月20日 17:56, zhuyj 写道:
> On 01/20/2016 05:47 PM, Wengang Wang wrote:
>>
>>
>> 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 <[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?
>>>> 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?
>
> dev_queue_xmit->ipip_tunnel_xmit->ip_tunnel_xmit->tnl_update_pmtu-> 
> skb_dst(skb)->ops->update_pmtu
For ipip,  yes seems update_pmtu is called in line for each call of 
queue_xmit.  Do you know if it's a good configuration for ipip + bonding?
Other's comment and suggestion?

thanks,
wengang