Re: [PATCH 5.10] net: mdio: fix unbalanced fwnode reference count in mdio_device_release()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Fri, Jan 16, 2026 at 11:14:45AM +0100, David Nyström wrote:
> [ Upstream commit cb37617687f2bfa5b675df7779f869147c9002bd ]
> 
> There is warning report about of_node refcount leak
> while probing mdio device:
> 
> OF: ERROR: memory leak, expected refcount 1 instead of 2,
> of_node_get()/of_node_put() unbalanced - destroy cset entry:
> attach overlay node /spi/soc@0/mdio@710700c0/ethernet@4
> 
> In of_mdiobus_register_device(), we increase fwnode refcount
> by fwnode_handle_get() before associating the of_node with
> mdio device, but it has never been decreased in normal path.
> Since that, in mdio_device_release(), it needs to call
> fwnode_handle_put() in addition instead of calling kfree()
> directly.
> 
> After above, just calling mdio_device_free() in the error handle
> path of of_mdiobus_register_device() is enough to keep the
> refcount balanced.
> 
> (cherry picked from commit cb37617687f2bfa5b675df7779f869147c9002bd)
> 
> Fixes: a9049e0c513c ("mdio: Add support for mdio drivers.")
> Signed-off-by: Zeng Heng <zengheng4@huawei.com>
> Reviewed-by: Yang Yingliang <yangyingliang@huawei.com>
> Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> Link: https://lore.kernel.org/r/20221203073441.3885317-1-zengheng4@huawei.com
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> Signed-off-by: David Nyström <david.nystrom@est.tech>
> ---
> This series backports 1 commit(s) to the 5.10 stable tree.
> ---
>  drivers/net/mdio/of_mdio.c    | 3 ++-
>  drivers/net/phy/mdio_device.c | 2 ++
>  2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/mdio/of_mdio.c b/drivers/net/mdio/of_mdio.c
> index b254127cea50..355c3ee21cd7 100644
> --- a/drivers/net/mdio/of_mdio.c
> +++ b/drivers/net/mdio/of_mdio.c
> @@ -168,8 +168,9 @@ static int of_mdiobus_register_device(struct mii_bus *mdio,
>  	/* All data is now stored in the mdiodev struct; register it. */
>  	rc = mdio_device_register(mdiodev);
>  	if (rc) {
> +		device_set_node(&mdiodev->dev, NULL);
> +		fwnode_handle_put(fwnode);
>  		mdio_device_free(mdiodev);
> -		of_node_put(child);
>  		return rc;
>  	}
>  
> diff --git a/drivers/net/phy/mdio_device.c b/drivers/net/phy/mdio_device.c
> index 797c41f5590e..f72d18ee2792 100644
> --- a/drivers/net/phy/mdio_device.c
> +++ b/drivers/net/phy/mdio_device.c
> @@ -21,6 +21,7 @@
>  #include <linux/slab.h>
>  #include <linux/string.h>
>  #include <linux/unistd.h>
> +#include <linux/property.h>
>  
>  void mdio_device_free(struct mdio_device *mdiodev)
>  {
> @@ -30,6 +31,7 @@ EXPORT_SYMBOL(mdio_device_free);
>  
>  static void mdio_device_release(struct device *dev)
>  {
> +	fwnode_handle_put(dev->fwnode);
>  	kfree(to_mdio_device(dev));
>  }
>  
> 
> ---
> base-commit: f964b940099f9982d723d4c77988d4b0dda9c165
> change-id: 20260115-backport_cb37617687f2_20260115100804-bb6cefe39d44
> 
> Best regards,
> --  
> David Nyström <david.nystrom@est.tech>
> 

Breaks the build, how did you test this:

drivers/net/mdio/of_mdio.c: In function ‘of_mdiobus_register_device’:
drivers/net/mdio/of_mdio.c:172:35: error: ‘fwnode’ undeclared (first use in this function); did you mean ‘inode’?
  172 |                 fwnode_handle_put(fwnode);
      |                                   ^~~~~~
      |                                   inode