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

On 01/20/2016 02:24 PM, zhuyj wrote:

On 01/20/2016 01:32 PM, Wengang Wang wrote:

quoted

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 <redacted>
---
  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_upper_get_next_dev_rcu is better? I am not sure.

Best Regards!
Zhu Yanjun

quoted

+    }
+    if (master)
+        oif = master->ifindex;
+    else
+        oif = skb->dev->ifindex;
        __build_flow_key(fl4, sk, iph, oif, tos, prot, mark, 0);
  }