netdev - Re: [PATCH net 0/2] Fix mdiobus users with devres

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Date:   Tue, 21 Sep 2021 09:32:49 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     netdev <netdev@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Wolfram Sang <wsa@...nel.org>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>, linux-spi@...r.kernel.org,
        Alvin Šipraga <alsi@...g-olufsen.dk>,
        Lino Sanfilippo <LinoSanfilippo@....de>
Subject: Re: [PATCH net 0/2] Fix mdiobus users with devres

On Mon, Sep 20, 2021 at 11:42 PM Vladimir Oltean
<vladimir.oltean@....com> wrote:
>
> Commit ac3a68d56651 ("net: phy: don't abuse devres in
> devm_mdiobus_register()") by Bartosz Golaszewski has introduced two
> classes of potential bugs by making the devres callback of
> devm_mdiobus_alloc stop calling mdiobus_unregister.
>
> The exact buggy circumstances are presented in the individual commit
> messages. I have searched the tree for other occurrences, but at the
> moment:
>
> - for issue (a) I have no concrete proof that other buses except SPI and
>   I2C suffer from it, and the only SPI or I2C device drivers that call
>   of_mdiobus_alloc are the DSA drivers that leave a NULL
>   ds->slave_mii_bus and a non-NULL ds->ops->phy_read, aka ksz9477,
>   ksz8795, lan9303_i2c, vsc73xx-spi.
>
> - for issue (b), all drivers which call of_mdiobus_alloc either use
>   of_mdiobus_register too, or call mdiobus_unregister sometime within
>   the ->remove path.
>
> Although at this point I've seen enough strangeness caused by this
> "device_del during ->shutdown" that I'm just going to copy the SPI and
> I2C subsystem maintainers to this patch series, to get their feedback
> whether they've had reports about things like this before. I don't think
> other buses behave in this way, it forces SPI and I2C devices to have to
> protect themselves from a really strange set of issues.
>
> Vladimir Oltean (2):
>   net: dsa: don't allocate the slave_mii_bus using devres
>   net: dsa: realtek: register the MDIO bus under devres
>
>  drivers/net/dsa/realtek-smi-core.c |  2 +-
>  net/dsa/dsa2.c                     | 12 +++++++++---
>  2 files changed, 10 insertions(+), 4 deletions(-)
>
> --
> 2.25.1
>

Hi Vladimir,

Thanks for the detailed description and sorry for the trouble this
caused. I will revisit this and go through the drivers using those
functions again and possibly come up with some improvement.

Acked-by: Bartosz Golaszewski <brgl@...ev.pl>

Bartosz