netdev - Re: [PATCH] net: take care of bonding in build_skb_flow

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Message-ID: <20160121083506.GA2251@nanopsycho.orion>
Date:	Thu, 21 Jan 2016 09:35:06 +0100
From:	Jiri Pirko <jiri@...nulli.us>
To:	Wengang Wang <wen.gang.wang@...cle.com>
Cc:	netdev@...r.kernel.org, sd@...asysnail.net,
	jay.vosburgh@...onical.com, zyjzyj2000@...il.com
Subject: Re: [PATCH] net: take care of bonding in build_skb_flow_key (v4)

Thu, Jan 21, 2016 at 06:32:58AM CET, wen.gang.wang@...cle.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.wang@...cle.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. Note that you may have bond over bond or bridge over
bond or other scenarios, which this patch ignores.