netdev - Re: [PATCH net] ip[6]: don't register inet[6]dev when dev is down

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Message-ID: <CAM_iQpXMR6RmJX52=7qrGVKopvGCiabS2sUOCf2Dvjhe4wLAzA@mail.gmail.com>
Date:   Thu, 6 Jul 2017 11:16:43 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc:     David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Hongjun Li <hongjun.li@...nd.com>
Subject: Re: [PATCH net] ip[6]: don't register inet[6]dev when dev is down

On Thu, Jul 6, 2017 at 5:08 AM, Nicolas Dichtel
<nicolas.dichtel@...nd.com> wrote:
> Le 06/07/2017 à 00:43, Cong Wang a écrit :
>> On Wed, Jul 5, 2017 at 8:57 AM, Nicolas Dichtel
>> <nicolas.dichtel@...nd.com> wrote:
>>> When a device changes from one netns to another, it's first unregistered,
>>> then the netns reference is updated and the dev is registered in the new
>>> netns. Thus, when a slave moves to another netns, it is first
>>> unregistered. This triggers a NETDEV_UNREGISTER event which is caught by
>>> the bonding driver. The driver calls bond_release(), which calls
>>> dev_set_mtu() and thus triggers NETDEV_CHANGEMTU (the device is still in
>>> the old netns).
>>
>> I think in this special case it is meaningless to send
>> NETDEV_CHANGEMTU, because the device is dying within
>> its old netns, who still cares about its mtu change?
>>
>> Something like the attached patch...
> Yes, your patch seems good and I hesitated with something like this.
> But I don't see a valid case where the inet[6]dev must be created on a down
> interface. I think the patch is valid, even with your patch.

Your patch is more risky because it affects normal CHANGEMTU path,
I am not sure if it is correct to not to add idev when it is down either.

This is a very unusual path, we don't have to take the risk.