netdev - Re: [PATCH net] net/ipv6: do not copy DST

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Message-ID: <CAPNVh5f3_GPpvV6nequZ8JNBhMVVOpEsJQ_XRfTN-+eaMPOWpw@mail.gmail.com>
Date:   Mon, 17 Sep 2018 09:11:35 -0700
From:   Peter Oskolkov <posk@...gle.com>
To:     dsahern@...il.com
Cc:     davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH net] net/ipv6: do not copy DST_NOCOUNT flag on rt init

On Thu, Sep 13, 2018 at 9:11 PM David Ahern <dsahern@...il.com> wrote:
>
> On 9/13/18 1:38 PM, Peter Oskolkov wrote:
>
> > diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> > index 3eed045c65a5..a3902f805305 100644
> > --- a/net/ipv6/route.c
> > +++ b/net/ipv6/route.c
> > @@ -946,7 +946,7 @@ static void ip6_rt_init_dst_reject(struct rt6_info *rt, struct fib6_info *ort)
> >
> >  static void ip6_rt_init_dst(struct rt6_info *rt, struct fib6_info *ort)
> >  {
> > -     rt->dst.flags |= fib6_info_dst_flags(ort);
> > +     rt->dst.flags |= fib6_info_dst_flags(ort) & ~DST_NOCOUNT;
>
> I think my mistake is setting dst.flags in ip6_rt_init_dst. Flags
> argument is passed to ip6_dst_alloc which is always invoked before
> ip6_rt_copy_init is called which is the only caller of ip6_rt_init_dst.

ip6_rt_cache_alloc calls ip6_dst_alloc with zero as flags; and only
one flag is copied later (DST_HOST) outside of ip6_rt_init_dst().
If the flag assignment is completely removed from ip6_rt_init_dst(),
then DST_NOPOLICY flag will be lost.

Which may be OK, but is more than what this patch tries to solve (do not
copy DST_NOCOUNT flag).

>
> >
> >       if (ort->fib6_flags & RTF_REJECT) {
> >               ip6_rt_init_dst_reject(rt, ort);
> >
>