netdev - Re: [PATCH v2] net: mdio: fix unbalanced fwnode reference count in mdio_device

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Message-ID: <71ae37d6-b5cf-d407-be4b-0c8b3c9f01d7@kylinos.cn>
Date: Wed, 27 Nov 2024 11:14:06 +0800
From: luoxuanqiang <luoxuanqiang@...inos.cn>
To: Zeng Heng <zengheng4@...wei.com>, hkallweit1@...il.com,
 edumazet@...gle.com, pabeni@...hat.com, kuba@...nel.org,
 davem@...emloft.net, andrew@...n.ch, f.fainelli@...il.com,
 linux@...linux.org.uk
Cc: liwei391@...wei.com, netdev@...r.kernel.org
Subject: Re: [PATCH v2] net: mdio: fix unbalanced fwnode reference count in
 mdio_device_release()

Hi Heng,

在 2024/11/22 15:59, luoxuanqiang 写道:
> Hi Heng,
>
> 在 2022/12/3 15:34, Zeng Heng 写道:
>> 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.
>>
>> Fixes: a9049e0c513c ("mdio: Add support for mdio drivers.")
>> Signed-off-by: Zeng Heng <zengheng4@...wei.com>
>> Reviewed-by: Yang Yingliang <yangyingliang@...wei.com>
>> ---
>>   changes in v2:
>>    - Add operation about setting device node as NULL-pointer.
>>      There is no practical changes.
>>    - Add reviewed-by tag.
>> ---
>>   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 796e9c7857d0..510822d6d0d9 100644
>> --- a/drivers/net/mdio/of_mdio.c
>> +++ b/drivers/net/mdio/of_mdio.c
>> @@ -68,8 +68,9 @@ 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);
> According to my understanding, the process flow of mdio_device_free() is
> as follows:
> mdio_device_free()
>     -> put_device()
>         ->kobject_put()
>             ->kobject_release()
>                 ->device_release()
>                     ->mdio_device_release()
>                     //Here, it will be called once fwnode_handle_put();
>
> Why is it necessary to add fwnode_handle_put(fwnode) again here? In the
> body of your email, you described that mdio_device_free() is sufficient
> to keep refcount balanced, and it was not added in the v1.
> Could you please explain the reason for this?
> I am looking forward to your response :)
>
> Thanks
> Xuanqiang
I noticed that I had missed the fact that you had already disconnected
the relationship between dev and node by calling
device_set_node(&mdiodev->dev, NULL). Even though it would go through
fwnode_handle_put() again, it would not have any effect.

Thanks
>>           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 250742ffdfd9..044828d081d2 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));
>>   }
>