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

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Date:   Tue, 21 Sep 2021 00:42:07 +0300
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     netdev@...r.kernel.org
Cc:     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>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Wolfram Sang <wsa@...nel.org>, 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: [PATCH net 0/2] Fix mdiobus users with devres

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