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

From: zhuyj <[email-masked]>
Date: Wed, 20 Jan 2016 14:24:06 +0800

On 01/20/2016 01:32 PM, Wengang Wang 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 | 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.

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