netdev - Re: ordering of call to unbind() in usbnet

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Date:   Thu, 31 Mar 2022 11:20:50 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     Oleksij Rempel <o.rempel@...gutronix.de>,
        Lukas Wunner <lukas@...ner.de>
CC:     Andrew Lunn <andrew@...n.ch>, Oliver Neukum <oneukum@...e.com>,
        Oleksij Rempel <linux@...pel-privat.de>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: ordering of call to unbind() in usbnet_disconnect



On 27.03.22 10:37, Oleksij Rempel wrote:
> On Sat, Mar 26, 2022 at 02:04:30PM +0100, Lukas Wunner wrote:
>> On Sat, Mar 26, 2022 at 01:49:28PM +0100, Andrew Lunn wrote:
>>> On Sat, Mar 26, 2022 at 01:39:29PM +0100, Lukas Wunner wrote:
>>>
>>>> On probe, they first attach the PHY, then register the netdev.
>>>> On remove, they detach the PHY, then unregister the netdev.
>>>>
>>>> Is it legal to detach the PHY from a registered (potentially running)
>>>> netdev? It looks wrong to me.
>>> I think the network stack guarantee that the close() method is called
>>> before unregister completes. It is a common pattern to attach the PHY
>>> in open() and detach it in close(). The stack itself should not be
>>> using the PHY when it is down, the exception being IOCTL handlers
>>> which people often get wrong.
>> But the PHY is detached from a *running* netdev *before* that netdev
>> is unregistered (and closed).  Is that really legal?
> IMO, it reflects, more or less, the reality of devices with SFP modules.
> The PHY can be physically removed from running netdev. At same time,
> netdev should be registered and visible for the user, even if PHY is not
> physically attached.
>
>
Hi,

this makes sense, but the relevance to the question of how to do an
unplug of the whole device is indirect, isn't it? I am afraid, putting my
maintainer's hat on, I have to point on that we have a stable tree for
which we will need some solution.

Nor can usbnet exclusively cater to device that expose their PHY
over MDIO. (or at all really). Intuitively I must say that exactly reversing
the order of probe() in disconnect() is kind of the default.
If there is a need to deviate from that, of course we will acomodate that,
but making this the exclusive order is another matter.

I really get that you want to discuss this matter exhaustively, but we
need to
come to some kind of conclusion.

    Regards
        Oliver