netdev - [PATCH net 6/7] net: dsa: mt7530: fix kernel bug in mdiobus

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Message-Id: <20220207161553.579933-7-vladimir.oltean@nxp.com>
Date:   Mon,  7 Feb 2022 18:15:52 +0200
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     netdev@...r.kernel.org
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        DENG Qingfang <dqfext@...il.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        UNGLinuxDriver@...rochip.com,
        Oleksij Rempel <linux@...pel-privat.de>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Rafael Richter <rafael.richter@....de>,
        Daniel Klauer <daniel.klauer@....de>
Subject: [PATCH net 6/7] net: dsa: mt7530: fix kernel bug in mdiobus_free() when unbinding

Nobody in this driver calls mdiobus_unregister(), which is necessary if
mdiobus_register() completes successfully. So if the devres callbacks
that free the mdiobus get invoked (this is the case when unbinding the
driver), mdiobus_free() will BUG if the mdiobus is still registered,
which it is.

My speculation is that this is due to the fact that prior to commit
ac3a68d56651 ("net: phy: don't abuse devres in devm_mdiobus_register()")
from June 2020, _devm_mdiobus_free() used to call mdiobus_unregister().
But at the time that the mt7530 support was introduced in May 2021, the
API was already changed. It's therefore likely that the blamed patch was
developed on an older tree, and incorrectly adapted to net-next. This
makes the Fixes: tag correct.

Fix the problem by using the devres variant of mdiobus_register.

Fixes: ba751e28d442 ("net: dsa: mt7530: add interrupt support")
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 drivers/net/dsa/mt7530.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
index bc77a26c825a..f74f25f479ed 100644
--- a/drivers/net/dsa/mt7530.c
+++ b/drivers/net/dsa/mt7530.c
@@ -2074,7 +2074,7 @@ mt7530_setup_mdio(struct mt7530_priv *priv)
 	if (priv->irq)
 		mt7530_setup_mdio_irq(priv);

-	ret = mdiobus_register(bus);
+	ret = devm_mdiobus_register(dev, bus);
 	if (ret) {
 		dev_err(dev, "failed to register MDIO bus: %d\n", ret);
 		if (priv->irq)
-- 
2.25.1