Re: [PATCH v3] udp reuseport: fix packet of same flow hashed to different socket

[Eric Dumazet]

On Sun, 2016-06-12 at 20:43 +0800, Su Xuemin wrote:
> From: "Su, Xuemin" <suxm@xxxxxxxxxxxxxxxxxx>
...

> Signed-off-by: Su, Xuemin <suxm@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> ---

First, I want to thank you for this very high quality submission,
especially if this is your first linux kernel patch.

I have one additional comment to make :



>  		if (score > badness) {
>  			reuseport = sk->sk_reuseport;
> @@ -556,14 +510,20 @@ struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr,
>  					  daddr, hnum, dif,
>  					  hslot2, slot2, skb);
>  		if (!result) {
> +			unsigned int old = hash2;
>  			hash2 = udp4_portaddr_hash(net, htonl(INADDR_ANY), hnum);
> +
> +			/* avoid search the same slot again. */
> +			if (unlikely(old == hash2))
> +				return result;
> +

Technically speaking, what matters is the slot, not the hash value
(32bit)

So I would save in old, slot2

>  			slot2 = hash2 & udptable->mask;

And here perform the check
			if (unlikely(slot2 != old_slot))
				return result;

>  			hslot2 = &udptable->hash2[slot2];
>  			if (hslot->count < hslot2->count)
>  				goto begin;


(Same remark applies in IPv6)

Thanks !