Bonding driver has bad load balancing for forwarded traffic, 3.7+

["Vitaly V. Bursov" <vitalyb@telenet.dn.ua>]

Hello,

I have a bonding device (mode=802.3ad xmit_hash_policy=layer2+3 miimon=300) and
for kernels <3.7 forwarded IPv4 traffic distributed fine across multiple physical
links. Ethernet cards are Intel 82576 with igb driver (various versions).

3.7 and 3.8 kernels tend to fully utilize only one link and leave the others almost idling.

Replacing bond_xmit_hash_policy_* functions with older ones (3.6 kernel) looks like
resolves the issue (but I haven't tested it thoroughly).

So, I added
         printk(KERN_INFO "hash_policy: protocol = %d, skb_network_header_len = %d, %d %d\n",
             skb->protocol, skb_network_header_len(skb),
             skb_headlen(skb), skb_network_offset(skb));
to bond_xmit_hash_policy_l23() of bond_main.c

and got this:
[   65.280831] hash_policy: protocol = 8, skb_network_header_len = 0, 74 14
[   65.280835] hash_policy: protocol = 8, skb_network_header_len = 0, 74 14
[   65.280839] hash_policy: protocol = 8, skb_network_header_len = 0, 74 14
[   65.280843] hash_policy: protocol = 8, skb_network_header_len = 0, 74 14
[   65.280847] hash_policy: protocol = 8, skb_network_header_len = 0, 74 14
[   65.280851] hash_policy: protocol = 8, skb_network_header_len = 0, 74 14

It's clear that the new check condition (skb_network_header_len(skb) >= sizeof(*iph))
fails here and hash policy fallbacks to l2 balancing.

I have no idea how to fix this besides removing this check completely, any
help would be appreciated.

-- 
Thanks
Vitaly