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

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Message-ID: <20220317210345.GA32093@wunner.de>
Date:   Thu, 17 Mar 2022 22:03:45 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     Oliver Neukum <oneukum@...e.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Oleksij Rempel <o.rempel@...gutronix.de>,
        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 Thu, Mar 17, 2022 at 04:53:34PM +0100, Oliver Neukum wrote:
> On 15.03.22 14:28, Andrew Lunn wrote:
> >>>> It was linked to unregistered/freed
> >>>> netdev. This is why my patch changing the order to call phy_disconnect()
> >>>> first and then unregister_netdev().
> >>> Unregistered yes, but freed no.  Here's the order before 2c9d6c2b871d:
> >>>
> >>>   usbnet_disconnect()
> >>>     unregister_netdev()
> >>>     ax88772_unbind()
> >>>       phy_disconnect()
> >>>     free_netdev()
> >>>
> >>> Is it illegal to disconnect a PHY from an unregistered, but not yet freed
> >>> net_device?
> > There are drivers which unregistering and then calling
> > phy_disconnect. In general that should be a valid pattern. But more
> > MAC drivers actually connect the PHY on open and disconnect it on
> > close. So it is less well used.
> 
> this is an interesting discussion, but what practical conclusion
> do we draw from it? Is it necessary to provide both orders
> of notifying the subdriver, or isn't it?

As far as I'm concerned, more time for analysis is needed
to understand what the issues really are and how to solve them.

Commit a049a30fc27c (for a different USB Ethernet driver -- smsc95xx.c)
seems to imply that unregistering the netdev before phy_disconnect()
doesn't work.

Thanks,

Lukas