netdev - [PATCH net-next v1] dsa: qca8k: Use nested lock to avoid splat

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Message-Id: <20241110175955.3053664-1-andrew@lunn.ch>
Date: Sun, 10 Nov 2024 18:59:55 +0100
From: Andrew Lunn <andrew@...n.ch>
To: <edumazet@...gle.com>,
	<kuba@...nel.org>,
	<pabeni@...hat.com>,
	<davem@...emloft.net>
Cc: netdev <netdev@...r.kernel.org>,
	ansuelsmth@...il.com,
	Vladimir Oltean <vladimir.oltean@....com>,
	Andrew Lunn <andrew@...n.ch>
Subject: [PATCH net-next v1] dsa: qca8k: Use nested lock to avoid splat

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>
---
 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 f8d8c70642c4..59b4a7240b58 100644
--- a/drivers/net/dsa/qca/qca8k-8xxx.c
+++ b/drivers/net/dsa/qca/qca8k-8xxx.c
@@ -673,7 +673,7 @@ 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
-- 
2.45.2