netdev - [PATCH net] net: phy: add a note about refcounting

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Message-Id: <E1mwj8r-00FjNH-Ix@rmk-PC.armlinux.org.uk>
Date:   Mon, 13 Dec 2021 11:05:13 +0000
From:   "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>
To:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH net] net: phy: add a note about refcounting

Recently, a patch has been submitted to "fix" the refcounting for a DT
node in of_mdiobus_link_mdiodev(). This is not a leaked refcount. The
refcount is passed to the new device.

Sadly, coccicheck identifies this location as a leaked refcount, which
means we're likely to keep getting patches to "fix" this. However,
fixing this will cause breakage. Add a comment to state that the lack
of of_node_put() here is intentional.

Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
---
 drivers/net/phy/mdio_bus.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
index c204067f1890..c198722e4871 100644
--- a/drivers/net/phy/mdio_bus.c
+++ b/drivers/net/phy/mdio_bus.c
@@ -460,6 +460,9 @@ static void of_mdiobus_link_mdiodev(struct mii_bus *bus,
 
 		if (addr == mdiodev->addr) {
 			device_set_node(dev, of_fwnode_handle(child));
+			/* The refcount on "child" is passed to the mdio
+			 * device. Do _not_ use of_node_put(child) here.
+			 */
 			return;
 		}
 	}
-- 
2.30.2