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

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

[Andrew Lunn]

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@lunn.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

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

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Sun, 10 Nov 2024 18:59:55 +0100 you wrote:
> 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@lunn.ch>
> 
> [...]

Here is the summary with links:
  - [net-next,v1] dsa: qca8k: Use nested lock to avoid splat
    https://git.kernel.org/netdev/net-next/c/078e0d596f7b

You are awesome, thank you!
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