netdev - Re: [PATCH net] ipv6: make ip6_create_rt_rcu return ip6_null

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Date:   Tue, 19 Mar 2019 09:19:56 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Wei Wang <weiwan@...gle.com>, David Ahern <dsa@...ulusnetworks.com>
Cc:     Xin Long <lucien.xin@...il.com>,
        network dev <netdev@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH net] ipv6: make ip6_create_rt_rcu return ip6_null_entry
 instead of NULL

Hi,

On Mon, 2019-03-18 at 14:30 -0700, Wei Wang wrote:
> On Mon, Mar 18, 2019 at 12:48 PM David Ahern <dsa@...ulusnetworks.com> wrote:
> > On 3/18/19 12:36 PM, Xin Long wrote:
> > > diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> > > index 4ef4bbd..754777d 100644
> > > --- a/net/ipv6/route.c
> > > +++ b/net/ipv6/route.c
> > > @@ -1040,13 +1040,17 @@ static struct rt6_info *ip6_create_rt_rcu(struct fib6_info *rt)
> > >       struct rt6_info *nrt;
> > > 
> > >       if (!fib6_info_hold_safe(rt))
> > > -             return NULL;
> > > +             goto fallback;
> > > 
> > >       nrt = ip6_dst_alloc(dev_net(dev), dev, flags);
> > > -     if (nrt)
> > > +     if (nrt) {
> > >               ip6_rt_copy_init(nrt, rt);
> > > -     else
> > > +     } else {
> > >               fib6_info_release(rt);
> > > +fallback:
> > > +             nrt = dev_net(dev)->ipv6.ip6_null_entry;
> > > +             dst_hold(&nrt->dst);
> > > +     }
> > > 
> > >       return nrt;
> > >  }
> > 
> > It seems appropriate for ip6_create_rt_rcu to always return an rt6_info
> > given its use and v6 design. Since ip6_dst_alloc can also fail
> > (e.g.,
> > exceed gc_thresh) the fallback case should apply to both.
> 
> Agree. We should take care of ip6_dst_alloc() as well.

AFAICS, if ip6_dst_alloc() fails/returns a NULL ptr, with this patch we
do enter the fallback path (and return a valid rt6_info). I think your
concerns are already addressed, what I'm missing ?!?

Thanks,

Paolo