[PATCH AUTOSEL 6.11 74/87] dsa: qca8k: Use nested lock to avoid splat

From: Sasha Levin
Date: Sun Nov 24 2024 - 09:33:48 EST


From: Andrew Lunn <andrew@xxxxxxx>

[ 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@xxxxxxx>
Link: https://patch.msgid.link/20241110175955.3053664-1-andrew@xxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
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 f8d8c70642c4f..59b4a7240b583 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
--
2.43.0