Subject: Re: [PATCH V4 net 2/2] net: fix tcp reset packet flowlabel for ipv6

From: Shaohua Li <[email-masked]>
Date: Mon, 31 Jul 2017 16:00:02 -0700

On Mon, Jul 31, 2017 at 03:35:02PM -0700, Cong Wang wrote:
> On Mon, Jul 31, 2017 at 3:19 PM, Shaohua Li <[email-masked]> wrote:
> >  static inline __be32 ip6_make_flowlabel(struct net *net, struct sk_buff *skb,
> >                                         __be32 flowlabel, bool autolabel,
> > -                                       struct flowi6 *fl6)
> > +                                       struct flowi6 *fl6, u32 hash)
> >  {
> > -       u32 hash;
> > -
> >         /* @flowlabel may include more than a flow label, eg, the traffic class.
> >          * Here we want only the flow label value.
> >          */
> > @@ -788,7 +786,8 @@ static inline __be32 ip6_make_flowlabel(struct net *net, struct sk_buff *skb,
> >              net->ipv6.sysctl.auto_flowlabels != IP6_AUTO_FLOW_LABEL_FORCED))
> >                 return flowlabel;
> >
> > -       hash = skb_get_hash_flowi6(skb, fl6);
> > +       if (skb)
> > +               hash = skb_get_hash_flowi6(skb, fl6);
> 
> 
> Why not just move skb_get_hash_flowi6() to its caller?
> This check is not necessary. If you don't want to touch
> existing callers, you can just introduce a wrapper:
> 
> 
> static inline __be32 ip6_make_flowlabel(struct net *net, struct sk_buff *skb,
>                                         __be32 flowlabel, bool autolabel,
>                                         struct flowi6 *fl6)
> {
>   u32 hash = skb_get_hash_flowi6(skb, fl6);
>   return __ip6_make_flowlabel(net, flowlabel, autolabel, hash);
> }

this will always call skb_get_hash_flowi6 for the fast path even auto flowlabel
is disabled. I thought we should avoid this.

> 
> And your code can just call:
> 
> __ip6_make_flowlabel(net, flowlabel, autolabel, sk->sk_txhash);