netdev - Re: [PATCH net 2/2] vlan: move dev_put into vlan_dev

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Date:   Wed, 9 Feb 2022 21:49:51 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Xin Long <lucien.xin@...il.com>,
        network dev <netdev@...r.kernel.org>,
        davem <davem@...emloft.net>,
        Ziyang Xuan <william.xuanziyang@...wei.com>
Subject: Re: [PATCH net 2/2] vlan: move dev_put into vlan_dev_uninit

On Wed, Feb 9, 2022 at 9:28 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Thu, 10 Feb 2022 11:40:42 +0800 Xin Long wrote:
> > > I think better fix would be to rewrite netdev_run_todo() to free the
> > > netdevs in any order they become ready. That's gonna solve any
> > > dependency problems and may even speed things up.
> >
> > What about I keep dev_put() in dev->priv_destructor()/vlan_dev_free() for
> > vlan as before, and fix this problem by using for_each_netdev_reverse()
> > in __rtnl_kill_links()?
> > It will make sense as the late added dev should be deleted early when
> > rtnl_link_unregister a rtnl_link_ops.
>
> Feels like sooner or later we'll run into a scenario when reversing will
> cause a problem. Or some data structure will stop preserving the order.
>
> Do you reckon rewriting netdev_run_todo() will be a lot of effort or
> it's too risky?

This is doable, and risky ;)

BTW, I have the plan of generalizing blackhole_netdev for IPv6,
meaning that we could perhaps get rid of the dependency
about loopback dev, being the last device in a netns being dismantled.