netdev - Re: [PATCH] net: Fix device name resolving crash in default_device

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Date:   Sun, 17 Jun 2018 12:58:44 -0600
From:   David Ahern <dsahern@...il.com>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, daniel@...earbox.net,
        jakub.kicinski@...ronome.com, ast@...nel.org,
        linux@...musvillemoes.dk, john.fastabend@...il.com,
        brouer@...hat.com
Subject: Re: [PATCH] net: Fix device name resolving crash in
 default_device_exit()

On 6/15/18 3:44 AM, Kirill Tkhai wrote:
> Hm, but is this a likely case, when real device is moved to net ns, so it
> requires moving to init_net back? It seems the most devices moved to !init_net
> are virtual and they just destroyed in default_device_exit_batch(). Or we have
> more devices to care here?
> 
> I don't much want to insert here something like below:
> 
> 	if (__dev_get_by_name(&init_net, dev->name))
> 		snprintf(fb_name, IFNAMSIZ, "dev%d", dev->ifindex);
> 	err = dev_change_net_namespace(dev, &init_net, "dev%d");
> 
> because dev_change_net_namespace() is generic interface and it's used not only here,
> and this will crumble the code in corner cases.
> 
> Maybe you have better ideas about this?

There are a lot of use cases these days (e.g., switch NOS) with 1000's
(10's of 1000's) of netdevices. On top of that support for port netdevs
in a namespace to create virtual switches needs to happen (and I suspect
will happen in the next few years). That becomes one example where
netdevices representing physical ports can be pushed back to init_net.

That said, not many easy options at the moment for the bug you are fixing.

Further, panic'ing a node because the move back to init_net fails is
just wrong.