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

[Wengang Wang]

在 2016年01月22日 14:52, Jiri Pirko 写道:

Fri, Jan 22, 2016 at 05:21:28AM CET, wen.gang.w...@oracle.com wrote:

在 2016年01月21日 16:35, Jiri Pirko 写道:

Thu, Jan 21, 2016 at 06:32:58AM CET, wen.gang.w...@oracle.com 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.w...@oracle.com>
---
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.

Yep, to make code better. I can do it.

thanks,
wengang

thanks,
wengang