linux-kernel - Re: [PATCH] net: dsa: microchip: fix mdio parent bus reference leak

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Message-ID: <20251123113643.cf2kc7i5cvdkkaf2@skbuf>
Date: Sun, 23 Nov 2025 13:36:43 +0200
From: Vladimir Oltean <olteanv@...il.com>
To: Ma Ke <make24@...as.ac.cn>
Cc: woojung.huh@...rochip.com, UNGLinuxDriver@...rochip.com, andrew@...n.ch,
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, o.rempel@...gutronix.de, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] net: dsa: microchip: fix mdio parent bus reference leak

On Fri, Nov 21, 2025 at 12:20:00PM +0800, Ma Ke wrote:
> In ksz_mdio_register(), when of_mdio_find_bus() is called to get the
> parent MDIO bus, it increments the reference count of the underlying
> device. However, the reference are not released in error paths or
> during switch teardown, causing a reference leak.
> 
> Add put_device() in the error path of ksz_mdio_register() and
> ksz_teardown() to release the parent bus.
> 
> Found by code review.
> 
> Cc: stable@...r.kernel.org
> Fixes: 9afaf0eec2ab ("net: dsa: microchip: Refactor MDIO handling for side MDIO access")
> Signed-off-by: Ma Ke <make24@...as.ac.cn>
> ---
>  drivers/net/dsa/microchip/ksz_common.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c
> index 933ae8dc6337..49c0420a6df8 100644
> --- a/drivers/net/dsa/microchip/ksz_common.c
> +++ b/drivers/net/dsa/microchip/ksz_common.c
> @@ -2795,6 +2795,11 @@ static int ksz_mdio_register(struct ksz_device *dev)
>  	}
>  
>  put_mdio_node:
> +	if (ret && dev->parent_mdio_bus) {
> +		put_device(&dev->parent_mdio_bus->dev);
> +		dev->parent_mdio_bus = NULL;
> +	}
> +
>  	of_node_put(mdio_np);
>  	of_node_put(parent_bus_node);
>  
> @@ -3110,6 +3115,11 @@ static void ksz_teardown(struct dsa_switch *ds)
>  		ksz_irq_free(&dev->girq);
>  	}
>  
> +	if (dev->parent_mdio_bus) {
> +		put_device(&dev->parent_mdio_bus->dev);
> +		dev->parent_mdio_bus = NULL;
> +	}
> +
>  	if (dev->dev_ops->teardown)
>  		dev->dev_ops->teardown(ds);
>  }
> -- 
> 2.17.1
> 

Thank you for the patch.

I see 2 problems:

1. I'm not sure that releasing the reference to the parent_mdio_bus
   device is compatible with devres, since the MDIO bus created by
   ksz_mdio_register() will continue to exist after we release the
   parent_mdio_bus reference. I think it would be better to remove
   devres, introduce ksz_mdio_unregister(), and only release the
   reference once our MDIO bus is unregistered.

2. Error path handling is incomplete:

	ret = ksz_mdio_register(dev);
	if (ret < 0) {
		dev_err(dev->dev, "failed to register the mdio");
		goto out_ptp_clock_unregister;
	}

	ret = ksz_dcb_init(dev);
	if (ret)
		goto out_ptp_clock_unregister; // needs to call ksz_mdio_unregister()