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

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Message-ID: <1494348962.7796.88.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Tue, 09 May 2017 09:56:02 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     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 Tue, 2017-05-09 at 09:44 -0700, Cong Wang wrote:

> 
> Eric, how did you produce it?
> I guess it's because of nh_dev which is the only netdevice pointer inside
> fib_info. Let me take a deeper look.
> 

Nothing particular, I am using kexec to boot new kernels, and all my
attempts with your patch included demonstrated the issue.

eth0 is a bonding device, it might matter, I do not know.

We also have some tunnels, but unfortunately I can not provide a setup
that you could use on say a VM.

I can send you the .config if this can help

> >>
> >> I am assuming you are quite confident it is this change?
> >
> > At least, reverting the patch resolves the issue for me.
> >
> > Keeping fib (and their reference to netdev) is apparently too much,
> > we probably need to implement a refcount on the metrics themselves,
> > being stand alone objects.
> 
> I don't disagree, just that it may need to change too much code which
> goes beyond a stable candidate.

Well, your choice, but dealing with a full blown fib and its
dependencies look fragile to me.