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

From: Wengang Wang <[email-masked]>
Date: Fri, 22 Jan 2016 12:21:28 +0800

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?

thanks,
wengang