netdev - Re: [PATCH net] net: mdiobus: remove unneccessary fwnode_handle

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Message-ID: <Y4gUQC+Gh4b/lr5f@lunn.ch>
Date:   Thu, 1 Dec 2022 03:41:04 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Yang Yingliang <yangyingliang@...wei.com>
Cc:     netdev@...r.kernel.org, hkallweit1@...il.com,
        linux@...linux.org.uk, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, ioana.ciornei@....com,
        calvin.johnson@....nxp.com, grant.likely@....com,
        zengheng4@...wei.com
Subject: Re: [PATCH net] net: mdiobus: remove unneccessary
 fwnode_handle_put() in the error path

On Wed, Nov 30, 2022 at 05:17:59PM +0800, Yang Yingliang wrote:
> If phy_device_register() or fwnode_mdiobus_phy_device_register()
> fail, phy_device_free() is called, the device refcount is decreased
> to 0, then fwnode_handle_put() is called in phy_device_release(),
> so the fwnode_handle_put() in the error path can be removed to avoid
> double put.
> 
> Fixes: cdde1560118f ("net: mdiobus: fix unbalanced node reference count")
> Reported-by: Zeng Heng <zengheng4@...wei.com>
> Tested-by: Zeng Heng <zengheng4@...wei.com>
> Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
> ---
>  drivers/net/mdio/fwnode_mdio.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/mdio/fwnode_mdio.c b/drivers/net/mdio/fwnode_mdio.c
> index eb344f6d4a7b..e584abda585b 100644
> --- a/drivers/net/mdio/fwnode_mdio.c
> +++ b/drivers/net/mdio/fwnode_mdio.c
> @@ -97,10 +97,8 @@ int fwnode_mdiobus_phy_device_register(struct mii_bus *mdio,
>  	 * register it
>  	 */
>  	rc = phy_device_register(phy);
> -	if (rc) {
> -		fwnode_handle_put(child);
> +	if (rc)
>  		return rc;
> -	}

The current code is:

        /* Associate the fwnode with the device structure so it
         * can be looked up later
         */
        fwnode_handle_get(child);
        device_set_node(&phy->mdio.dev, child);

        /* All data is now stored in the phy struct;
         * register it
         */
        rc = phy_device_register(phy);
        if (rc) {
                fwnode_handle_put(child);
                return rc;
        }

The fwnode_handle_put(child) balances the earlier
fwnode_handle_get(child).

The code will look wrong without this balance. Please find a better
fix which actually looks correct.

    Andrew