linux-kernel - [PATCH AUTOSEL 6.1 42/48] dsa: qca8k: Use nested lock to avoid splat

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Message-ID: <20241124134950.3348099-42-sashal@kernel.org>
Date: Sun, 24 Nov 2024 08:49:05 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Andrew Lunn <andrew@...n.ch>,
	Jakub Kicinski <kuba@...nel.org>,
	Sasha Levin <sashal@...nel.org>,
	olteanv@...il.com,
	davem@...emloft.net,
	edumazet@...gle.com,
	pabeni@...hat.com,
	florian.fainelli@...adcom.com,
	alsi@...g-olufsen.dk,
	ansuelsmth@...il.com,
	michal.vokac@...ft.com,
	javier.carrasco.cruz@...il.com,
	rmk+kernel@...linux.org.uk,
	netdev@...r.kernel.org
Subject: [PATCH AUTOSEL 6.1 42/48] dsa: qca8k: Use nested lock to avoid splat

From: Andrew Lunn <andrew@...n.ch>

[ Upstream commit 078e0d596f7b5952dad8662ace8f20ed2165e2ce ]

qca8k_phy_eth_command() is used to probe the child MDIO bus while the
parent MDIO is locked. This causes lockdep splat, reporting a possible
deadlock. It is not an actually deadlock, because different locks are
used. By making use of mutex_lock_nested() we can avoid this false
positive.

Signed-off-by: Andrew Lunn <andrew@...n.ch>
Link: https://patch.msgid.link/20241110175955.3053664-1-andrew@lunn.ch
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/net/dsa/qca/qca8k-8xxx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/dsa/qca/qca8k-8xxx.c b/drivers/net/dsa/qca/qca8k-8xxx.c
index 641692f716f86..47e9b2c303831 100644
--- a/drivers/net/dsa/qca/qca8k-8xxx.c
+++ b/drivers/net/dsa/qca/qca8k-8xxx.c
@@ -551,7 +551,7 @@ qca8k_phy_eth_command(struct qca8k_priv *priv, bool read, int phy,
 	 * We therefore need to lock the MDIO bus onto which the switch is
 	 * connected.
 	 */
-	mutex_lock(&priv->bus->mdio_lock);
+	mutex_lock_nested(&priv->bus->mdio_lock, MDIO_MUTEX_NESTED);
 
 	/* Actually start the request:
 	 * 1. Send mdio master packet
-- 
2.43.0