netdev - Re: [PATCH net-next] net: phy: avoid NPE if read_page/write

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Date:   Wed, 16 Oct 2019 13:20:35 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Heiner Kallweit <hkallweit1@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        David Miller <davem@...emloft.net>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net: phy: avoid NPE if read_page/write_page
 callbacks are not available

On 10/16/19 12:53 PM, Heiner Kallweit wrote:
> Currently there's a bug in the module subsystem [0] preventing load of
> the PHY driver module on certain systems (as one symptom).
> This results in a NPE on such systems for the following reason:
> Instead of the correct PHY driver the genphy driver is loaded that
> doesn't implement the read_page/write_page callbacks. Every call to
> phy_read_paged() et al will result in a NPE therefore.
> 
> In parallel to fixing the root cause we should make sure that this one
> and maybe similar issues in other subsystems don't result in a NPE
> in phylib. So let's check for the callbacks before using them and warn
> once if they are not available.

Everywhere else in the PHY library we tend to do:

if (!phydev->drv)
	return -EIO;

maybe not the best choice for an error code, but we should be consistent.

Is the issue really that we do have a driver we are bound to, but
somehow we cannot resolve the read_page/write_page callbacks to a valid
function pointer?

> 
> [0] https://marc.info/?t=157072642100001&r=1&w=2
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
> ---
>  drivers/net/phy/phy-core.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/net/phy/phy-core.c b/drivers/net/phy/phy-core.c
> index 9412669b5..0ae1722ba 100644
> --- a/drivers/net/phy/phy-core.c
> +++ b/drivers/net/phy/phy-core.c
> @@ -689,11 +689,17 @@ EXPORT_SYMBOL_GPL(phy_modify_mmd);
>  
>  static int __phy_read_page(struct phy_device *phydev)
>  {
> +	if (WARN_ONCE(!phydev->drv->read_page, "read_page callback not available, PHY driver not loaded?\n"))
> +		return -EOPNOTSUPP;
> +
>  	return phydev->drv->read_page(phydev);
>  }
>  
>  static int __phy_write_page(struct phy_device *phydev, int page)
>  {
> +	if (WARN_ONCE(!phydev->drv->write_page, "write_page callback not available, PHY driver not loaded?\n"))
> +		return -EOPNOTSUPP;
> +
>  	return phydev->drv->write_page(phydev, page);
>  }
>  
> 


-- 
Florian