netdev - Re: [PATCH 5.10] net: mdio: fix unbalanced fwnode reference count in mdio_device

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Message-ID: <6e7347df-f1cf-e058-cc94-3112bf110b70@est.tech>
Date: Mon, 9 Feb 2026 09:16:01 +0100 (CET)
From: David Nyström <david.nystrom@....tech>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
cc: David Nyström <david.nystrom@....tech>, 
    stable@...r.kernel.org, Sasha Levin <sashal@...nel.org>, 
    netdev@...r.kernel.org
Subject: Re: [PATCH 5.10] net: mdio: fix unbalanced fwnode reference count
 in mdio_device_release()



On Tue, 3 Feb 2026, Greg Kroah-Hartman wrote:

> 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@...dio@...700c0/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@...wei.com>
>> Reviewed-by: Yang Yingliang <yangyingliang@...wei.com>
>> Reviewed-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
>> Link: https://lore.kernel.org/r/20221203073441.3885317-1-zengheng4@huawei.com
>> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
>> Signed-off-by: David Nyström <david.nystrom@....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@....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
>

Oops,
This patch was work-in-progress and should not have been sent your way.
Wont happen again.

Br,
David