netdev - Re: [PATCH 2/2] net: phy: Fix race conditions in the driver

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Message-ID: <20160819132417.GC7343@lunn.ch>
Date:   Fri, 19 Aug 2016 15:24:17 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Kedareswara rao Appana <appana.durga.rao@...inx.com>
Cc:     michal.simek@...inx.com, soren.brinkmann@...inx.com,
        appanad@...inx.com, f.fainelli@...il.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] net: phy: Fix race conditions in the driver

On Fri, Aug 19, 2016 at 06:18:11PM +0530, Kedareswara rao Appana wrote:
> This patch fixes the below race conditions in the driver.
> ---> Fix Opps after unload the driver as a module
> ---> Use spin locks where relevant.
> ---> Take reference on the external phy to prevent issues
> when phy driver is unloaded.

Each one of these should be an individual patch.

> 
> Reported-by: Andrew Lunn <andrew@...n.ch>
> Signed-off-by: Kedareswara rao Appana <appanad@...inx.com>
> ---
>  drivers/net/phy/xilinx_gmii2rgmii.c | 32 +++++++++++++++++++++++++++++++-
>  1 file changed, 31 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/phy/xilinx_gmii2rgmii.c b/drivers/net/phy/xilinx_gmii2rgmii.c
> index 7336fd0..cdd9d95 100644
> --- a/drivers/net/phy/xilinx_gmii2rgmii.c
> +++ b/drivers/net/phy/xilinx_gmii2rgmii.c
> @@ -34,6 +34,7 @@ struct gmii2rgmii {
>  	struct phy_driver *phy_drv;
>  	struct phy_driver conv_phy_drv;
>  	int addr;
> +	spinlock_t phy_lock;

The phy already have a lock.

>  };
>  
>  static int xgmiitorgmii_read_status(struct phy_device *phydev)
> @@ -55,7 +56,7 @@ static int xgmiitorgmii_read_status(struct phy_device *phydev)
>  		val |= BMCR_SPEED1000;
>  	else if (phydev->speed == SPEED_100)
>  		val |= BMCR_SPEED100;
> -	else
> +	else if (phydev->speed == SPEED_10)
>  		val |= BMCR_SPEED10;
  
I said you want to return an error is the PHY is using a speed your
converter cannot support. I don't see an error being raised here.

>  	err = mdiobus_write(phydev->mdio.bus, priv->addr, XILINX_GMII2RGMII_REG,
> @@ -71,6 +72,8 @@ int xgmiitorgmii_probe(struct mdio_device *mdiodev)
>  	struct device *dev = &mdiodev->dev;
>  	struct device_node *np = dev->of_node, *phy_node;
>  	struct gmii2rgmii *priv;
> +	struct mii_bus *bus;
> +	unsigned long flags;
>  
>  	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
>  	if (!priv)
> @@ -88,17 +91,43 @@ int xgmiitorgmii_probe(struct mdio_device *mdiodev)
>  		return -EPROBE_DEFER;
>  	}
>  
> +	spin_lock_init(&priv->phy_lock);
> +
> +	bus = priv->phy_dev->mdio.bus;
> +	if (!try_module_get(bus->owner)) {
> +		dev_err(dev, "failed to get the bus module\n");
> +		return -EIO;
> +	}

The comment at the top says you are taking a reference to the phy.
Here you take a reference to the mdio bus driver???

> +
> +	get_device(&priv->phy_dev->mdio.dev);
> +
>  	priv->addr = mdiodev->addr;
>  	priv->phy_drv = priv->phy_dev->drv;
>  	memcpy(&priv->conv_phy_drv, priv->phy_dev->drv,
>  	       sizeof(struct phy_driver));
>  	priv->conv_phy_drv.read_status = xgmiitorgmii_read_status;
>  	priv->phy_dev->priv = priv;
> +	spin_lock_irqsave(&priv->phy_lock, flags);
>  	priv->phy_dev->drv = &priv->conv_phy_drv;
> +	spin_unlock_irqrestore(&priv->phy_lock, flags);

And how is this spinlock protecting anything? 

> +
> +	dev_set_drvdata(dev, priv);
>  
>  	return 0;
>  }
>  
> +static void xgmiitorgmii_remove(struct mdio_device *mdiodev)
> +{
> +	struct gmii2rgmii *priv = dev_get_drvdata(&mdiodev->dev);
> +	struct mii_bus *bus;
> +
> +	bus = priv->phy_dev->mdio.bus;
> +
> +	put_device(&priv->phy_dev->mdio.dev);
> +	module_put(bus->owner);
> +	phy_disconnect(priv->phy_dev);

Why are you disconnecting the phy?

> +}
> +
>  static const struct of_device_id xgmiitorgmii_of_match[] = {
>  	{ .compatible = "xlnx,gmii-to-rgmii-1.0" },
>  	{},
> @@ -107,6 +136,7 @@ MODULE_DEVICE_TABLE(of, xgmiitorgmii_of_match);
>  
>  static struct mdio_driver xgmiitorgmii_driver = {
>  	.probe	= xgmiitorgmii_probe,
> +	.remove	= xgmiitorgmii_remove,
>  	.mdiodrv.driver = {
>  		.name = "xgmiitorgmii",
>  		.of_match_table = xgmiitorgmii_of_match,
> -- 
> 2.1.2
>