Subject: Re: [PATCH] net: take care of bonding in build_skb_flow_key (v4)

From: zhuyj <[email-masked]>
Date: Tue, 26 Jan 2016 15:45:52 +0800

On 01/22/2016 02:52 PM, Jiri Pirko wrote:
> Fri, Jan 22, 2016 at 05:21:28AM CET, [email-masked] wrote:
>>
>> 在 2016年01月21日 16:35, Jiri Pirko 写道:
>>> Thu, Jan 21, 2016 at 06:32:58AM CET, [email-masked] 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 | 9 +++++++++
>>>> 1 file changed, 9 insertions(+)
>>>>
>>>> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
>>>> index 85f184e..7e766b5 100644
>>>> --- a/net/ipv4/route.c
>>>> +++ b/net/ipv4/route.c
>>>> @@ -524,10 +524,19 @@ static void build_skb_flow_key(struct flowi4 *fl4, const struct sk_buff *skb,
>>>> {
>>>> 	const struct iphdr *iph = ip_hdr(skb);
>>>> 	int oif = skb->dev->ifindex;
>>>> +	struct net_device *master;
>>>> 	u8 tos = RT_TOS(iph->tos);
>>>> 	u8 prot = iph->protocol;
>>>> 	u32 mark = skb->mark;
>>>>
>>>> +	if (netif_is_bond_slave(skb->dev)) {
>>>> +		rcu_read_lock();
>>>> +		master = netdev_master_upper_dev_get_rcu(skb->dev);
>>>> +		if (master)
>>>> +			oif = master->ifindex;
>>>> +		rcu_read_unlock();
>>>> +	}
>>> This is certainly not correct as it should not be bond-specific but
>>> rather generic.
>> Then what you would suggest to fix it?
>>> Note that you may have bond over bond or bridge over
>>> bond or other scenarios, which this patch ignores.
>> I don't think bond over bond is a good configuration. Do you have a real use
>> case for that configuration?
> Stacking of multiple master devices is absolutelly common.
>
> You have to go in the upper tree all the way up, for all master device
> types.
I am not sure that the following can work or not.
Just a test patch.

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 85f184e..12b4982 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -523,10 +523,19 @@ 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 = skb->dev->ifindex;
+
+       if (skb->dev->flags & IFF_SLAVE) {
+               rcu_read_lock();
+               master = skb_dst(skb)->dev;
+               if (master)
+                       oif = master->ifindex;
+               rcu_read_unlock();
+       }

         __build_flow_key(fl4, sk, iph, oif, tos, prot, mark, 0);
  }

Thanks a lot.
Zhu Yanjun
>> thanks,
>> wengang