netdev - Re: [PATCH RESEND v3 5/9] of_mdio: fix MDIO phy device refcounting

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Message-ID: <CAL_JsqKhALmq-YyUZYKVzUpUW3oLeMN0edk6uDGhzHt7Qqe+iA@mail.gmail.com>
Date:	Thu, 24 Sep 2015 17:21:34 -0500
From:	Rob Herring <robh@...nel.org>
To:	Russell King <rmk+kernel@....linux.org.uk>
Cc:	Florian Fainelli <f.fainelli@...il.com>,
	David Miller <davem@...emloft.net>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Frank Rowand <frowand.list@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	Iyappan Subramanian <isubramanian@....com>,
	Keyur Chudgar <kchudgar@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
	Li Yang <leoli@...escale.com>,
	Michal Simek <michal.simek@...inx.com>,
	netdev <netdev@...r.kernel.org>,
	Robert Richter <rric@...nel.org>,
	Soren Brinkmann <soren.brinkmann@...inx.com>,
	Sunil Goutham <sgoutham@...ium.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND v3 5/9] of_mdio: fix MDIO phy device refcounting

On Thu, Sep 24, 2015 at 2:36 PM, Russell King
<rmk+kernel@....linux.org.uk> wrote:
> bus_find_device() is defined as:
>
>  * This is similar to the bus_for_each_dev() function above, but it
>  * returns a reference to a device that is 'found' for later use, as
>  * determined by the @match callback.
>
> and it does indeed return a reference-counted pointer to the device:
>
>         while ((dev = next_device(&i)))
>                 if (match(dev, data) && get_device(dev))
>                                         ^^^^^^^^^^^^^^^
>                         break;
>         klist_iter_exit(&i);
>         return dev;
>
> What that means is that when we're done with the struct device, we must
> drop that reference.  Neither of_phy_connect() nor of_phy_attach() did
> this when phy_connect_direct() or phy_attach_direct() failed.
>
> With our previous patch, phy_connect_direct() and phy_attach_direct()
> take a new refcount on the phy device when successful, so we can drop
> our local reference immediatley after these functions, whether or not
> they succeeded.
>
> Signed-off-by: Russell King <rmk+kernel@....linux.org.uk>

Acked-by: Rob Herring <robh@...nel.org>

> ---
>  drivers/of/of_mdio.c | 27 +++++++++++++++++++++++----
>  1 file changed, 23 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/of/of_mdio.c b/drivers/of/of_mdio.c
> index 1350fa25cdb0..a87a868fed64 100644
> --- a/drivers/of/of_mdio.c
> +++ b/drivers/of/of_mdio.c
> @@ -197,7 +197,8 @@ static int of_phy_match(struct device *dev, void *phy_np)
>   * of_phy_find_device - Give a PHY node, find the phy_device
>   * @phy_np: Pointer to the phy's device tree node
>   *
> - * Returns a pointer to the phy_device.
> + * If successful, returns a pointer to the phy_device with the embedded
> + * struct device refcount incremented by one, or NULL on failure.
>   */
>  struct phy_device *of_phy_find_device(struct device_node *phy_np)
>  {
> @@ -217,7 +218,9 @@ EXPORT_SYMBOL(of_phy_find_device);
>   * @hndlr: Link state callback for the network device
>   * @iface: PHY data interface type
>   *
> - * Returns a pointer to the phy_device if successful.  NULL otherwise
> + * If successful, returns a pointer to the phy_device with the embedded
> + * struct device refcount incremented by one, or NULL on failure. The
> + * refcount must be dropped by calling phy_disconnect() or phy_detach().
>   */
>  struct phy_device *of_phy_connect(struct net_device *dev,
>                                   struct device_node *phy_np,
> @@ -225,13 +228,19 @@ struct phy_device *of_phy_connect(struct net_device *dev,
>                                   phy_interface_t iface)
>  {
>         struct phy_device *phy = of_phy_find_device(phy_np);
> +       int ret;
>
>         if (!phy)
>                 return NULL;
>
>         phy->dev_flags = flags;
>
> -       return phy_connect_direct(dev, phy, hndlr, iface) ? NULL : phy;
> +       ret = phy_connect_direct(dev, phy, hndlr, iface);
> +
> +       /* refcount is held by phy_connect_direct() on success */
> +       put_device(&phy->dev);
> +
> +       return ret ? NULL : phy;
>  }
>  EXPORT_SYMBOL(of_phy_connect);
>
> @@ -241,17 +250,27 @@ EXPORT_SYMBOL(of_phy_connect);
>   * @phy_np: Node pointer for the PHY
>   * @flags: flags to pass to the PHY
>   * @iface: PHY data interface type
> + *
> + * If successful, returns a pointer to the phy_device with the embedded
> + * struct device refcount incremented by one, or NULL on failure. The
> + * refcount must be dropped by calling phy_disconnect() or phy_detach().
>   */
>  struct phy_device *of_phy_attach(struct net_device *dev,
>                                  struct device_node *phy_np, u32 flags,
>                                  phy_interface_t iface)
>  {
>         struct phy_device *phy = of_phy_find_device(phy_np);
> +       int ret;
>
>         if (!phy)
>                 return NULL;
>
> -       return phy_attach_direct(dev, phy, flags, iface) ? NULL : phy;
> +       ret = phy_attach_direct(dev, phy, flags, iface);
> +
> +       /* refcount is held by phy_attach_direct() on success */
> +       put_device(&phy->dev);
> +
> +       return ret ? NULL : phy;
>  }
>  EXPORT_SYMBOL(of_phy_attach);
>
> --
> 2.1.0
>
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