netdev - [PATCH stable 4.9] net: mdio-mux: fix unbalanced put

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Date:   Wed, 17 Nov 2021 10:03:08 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     stable@...r.kernel.org
Cc:     Corentin Labbe <clabbe.montjoie@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        "David S . Miller" <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        netdev@...r.kernel.org (open list:ETHERNET PHY LIBRARY),
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH stable 4.9] net: mdio-mux: fix unbalanced put_device

From: Corentin Labbe <clabbe.montjoie@...il.com>

commit 60f786525032432af1b7d9b8935cb12936244ccd upstream

mdio_mux_uninit() call put_device (unconditionally) because of
of_mdio_find_bus() in mdio_mux_init.
But of_mdio_find_bus is only called if mux_bus is empty.
If mux_bus is set, mdio_mux_uninit will print a "refcount_t: underflow"
trace.

This patch add a get_device in the other branch of "if (mux_bus)".

Signed-off-by: Corentin Labbe <clabbe.montjoie@...il.com>
Reviewed-by: Andrew Lunn <andrew@...n.ch>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
---
Note: this patch did not get any fixes tag, but it does fix issues
introduced by  fdf3b78df4d2 ("mdio: mux: Correct mdio_mux_init error
path issues").

Thanks!

 drivers/net/phy/mdio-mux.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/net/phy/mdio-mux.c b/drivers/net/phy/mdio-mux.c
index 599ce24c514f..456b64248e5d 100644
--- a/drivers/net/phy/mdio-mux.c
+++ b/drivers/net/phy/mdio-mux.c
@@ -117,6 +117,7 @@ int mdio_mux_init(struct device *dev,
 	} else {
 		parent_bus_node = NULL;
 		parent_bus = mux_bus;
+		get_device(&parent_bus->dev);
 	}
 
 	pb = devm_kzalloc(dev, sizeof(*pb), GFP_KERNEL);
@@ -182,9 +183,7 @@ int mdio_mux_init(struct device *dev,
 
 	devm_kfree(dev, pb);
 err_pb_kz:
-	/* balance the reference of_mdio_find_bus() took */
-	if (!mux_bus)
-		put_device(&parent_bus->dev);
+	put_device(&parent_bus->dev);
 err_parent_bus:
 	of_node_put(parent_bus_node);
 	return ret_val;
@@ -202,7 +201,6 @@ void mdio_mux_uninit(void *mux_handle)
 		cb = cb->next;
 	}
 
-	/* balance the reference of_mdio_find_bus() in mdio_mux_init() took */
 	put_device(&pb->mii_bus->dev);
 }
 EXPORT_SYMBOL_GPL(mdio_mux_uninit);
-- 
2.25.1