netdev - Re: [Patch net] ipv4: restore rt->fi for reference counting

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Message-ID: <CAM_iQpW0fJJXPS=FoTf-o4f5-mOC=mZYNP8=uqiUOmvX+CDwWw@mail.gmail.com>
Date:   Thu, 11 May 2017 17:07:15 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Julian Anastasov <ja@....bg>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [Patch net] ipv4: restore rt->fi for reference counting

On Wed, May 10, 2017 at 12:51 PM, Julian Anastasov <ja@....bg> wrote:
>         Oh, well, the sockets can hold cached dst.
> But if the promise is that rt->fi is used only as
> reference to metrics we have to find a way to drop
> the dev references at NETDEV_UNREGISTER time. If you
> set nh_dev to NULL then all lookups should check it
> for != NULL. The sockets will not walk NHs via rt->fi,
> i.e. the route lookups will get valid res.fi from trees,
> so it may work in this way.
>

So, if I understand you correctly it is safe to NULL'ing
nh_dev in NETDEV_UNREGISTER_FINAL, right?

If still not, how about transfer nh_dev's to loopback_dev
too in NETDEV_UNREGISTER? Like we transfer dst->dev.

I don't want to touch the fast path to check for NULL, as
it will change more code and slow down performance.

Thanks.