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

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Message-ID: <1494564948.7796.128.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Thu, 11 May 2017 21:55:48 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Julian Anastasov <ja@....bg>, 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 Thu, 2017-05-11 at 18:22 -0700, Cong Wang wrote:
> On Thu, May 11, 2017 at 5:07 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> > 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.
> 
> Finally I come up with the attached patch. Please let me know if
> I still miss anything.

You have not addressed my prior feedback, unless I am mistaken ?

fib_route_seq_show() and others do not expect fi->fib_dev suddenly
becoming NULL. 

RCU contract is more complicated than simply adding rcu grace period
before delete.

Thanks.