netdev - Re: [PATCH 2/2] net: phy: Ensure the MDIO bus module is held

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Message-ID: <CAGVrzcarnqLRnr97FRB-GVKwQLebpYtV7DXHp2ZTmm1gVfY30Q@mail.gmail.com>
Date:	Wed, 23 Jul 2014 11:22:20 -0700
From:	Florian Fainelli <f.fainelli@...il.com>
To:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
Cc:	netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Gregory Clement <gregory.clement@...e-electrons.com>
Subject: Re: [PATCH 2/2] net: phy: Ensure the MDIO bus module is held

2014-07-22 17:16 GMT-07:00 Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>:
> This commit adds proper module_{get,put} to prevent the MDIO bus module
> from being unloaded while the phydev is connected. By doing so, we fix
> a kernel panic produced when a MDIO driver is removed, but the phydev
> that relies on it is attached and running.
>
> Signed-off-by: Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
> ---
>  drivers/net/phy/phy_device.c | 23 ++++++++++++++++++++---
>  1 file changed, 20 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index 35d753d..a10dc47 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -575,6 +575,7 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
>                       u32 flags, phy_interface_t interface)
>  {
>         struct device *d = &phydev->dev;
> +       struct module *bus_module;
>         int err;
>
>         /* Assume that if there is no driver, that it doesn't
> @@ -599,6 +600,14 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
>                 return -EBUSY;
>         }
>
> +       /* Increment the bus module reference count */
> +       bus_module = phydev->bus->dev.driver ?
> +                    phydev->bus->dev.driver->owner : NULL;
> +       if (!try_module_get(bus_module)) {
> +               dev_err(&dev->dev, "failed to get the bus module\n");
> +               return -EIO;
> +       }
> +
>         phydev->attached_dev = dev;
>         dev->phydev = phydev;
>
> @@ -614,10 +623,14 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
>          */
>         err = phy_init_hw(phydev);
>         if (err)
> -               phy_detach(phydev);
> -       else
> -               phy_resume(phydev);
> +               goto err_module_put;
>
> +       phy_resume(phydev);
> +       return err;
> +
> +err_module_put:
> +       module_put(bus_module);
> +       phy_detach(phydev);

Since we are calling phy_detach() which is also attempting to do a
module_put(), does not that result in one too many calls to
module_put() on error path?

>         return err;
>  }
>  EXPORT_SYMBOL(phy_attach_direct);
> @@ -664,6 +677,10 @@ EXPORT_SYMBOL(phy_attach);
>  void phy_detach(struct phy_device *phydev)
>  {
>         int i;
> +
> +       if (phydev->bus->dev.driver)
> +               module_put(phydev->bus->dev.driver->owner);
> +
>         phydev->attached_dev->phydev = NULL;
>         phydev->attached_dev = NULL;
>         phy_suspend(phydev);
> --
> 2.0.1
>



-- 
Florian
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