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

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Message-ID: <8f59f82c-e1eb-f8f5-a646-189c0eac94cf@suse.com>
Date:   Thu, 31 Mar 2022 11:59:44 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     Lukas Wunner <lukas@...ner.de>, Oliver Neukum <oneukum@...e.com>
CC:     Oleksij Rempel <o.rempel@...gutronix.de>,
        Andrew Lunn <andrew@...n.ch>,
        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 31.03.22 11:30, Lukas Wunner wrote:
> I propose the below patch.  If you could provide more details on the
> regressions you've reported (+ ideally bugzilla links), I'll be happy
> to include them in the commit message.  Thanks!
There is no bugzilla, but the report can be found:
https://lore.kernel.org/netdev/CAG48ez0MHBbENX5gCdHAUXZ7h7s20LnepBF-pa5M=7Bi-jZrEA@mail.gmail.com/
>
> The commit made binding and unbinding of USB Ethernet asymmetrical:
> Before, usbnet_probe() first invoked the ->bind() callback and then
> register_netdev().  usbnet_disconnect() mirrored that by first invoking
> unregister_netdev() and then ->unbind().
>
> Since the commit, the order in usbnet_disconnect() is reversed and no
> longer mirrors usbnet_probe().
>
> One consequence is that a PHY disconnected (and stopped) in ->unbind()
> is afterwards stopped once more by unregister_netdev() as it closes the
> netdev before unregistering.  That necessitates a contortion in ->stop()
> because the PHY may only be stopped if it hasn't already been
> disconnected.
>
> Reverting the commit allows making the call to phy_stop() unconditional
> in ->stop() and also fixes the issues reported by Oliver.
Very well, but what prevents reintroducing the isssue this revert's
target was to fix?

    Regards
        Oliver