Re: [PATCH v5 01/11] firmware: raspberrypi: Keep count of all consumers

[Bartosz Golaszewski]

On Mon, Nov 23, 2020 at 7:38 PM Nicolas Saenz Julienne
<nsaenzjulienne@xxxxxxx> wrote:
>
> When unbinding the firmware device we need to make sure it has no
> consumers left. Otherwise we'd leave them with a firmware handle
> pointing at freed memory.
>
> Keep a reference count of all consumers and introduce rpi_firmware_put()
> which will permit automatically decrease the reference count upon
> unbinding consumer drivers.
>
> Suggested-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
> ---
>
> Changes since v3:
> - Use kref instead of waiting on refcount
>
>  drivers/firmware/raspberrypi.c             | 37 +++++++++++++++++++---
>  include/soc/bcm2835/raspberrypi-firmware.h |  2 ++
>  2 files changed, 35 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/firmware/raspberrypi.c b/drivers/firmware/raspberrypi.c
> index 30259dc9b805..ed793aef7851 100644
> --- a/drivers/firmware/raspberrypi.c
> +++ b/drivers/firmware/raspberrypi.c
> @@ -7,6 +7,7 @@
>   */
>
>  #include <linux/dma-mapping.h>
> +#include <linux/kref.h>
>  #include <linux/mailbox_client.h>
>  #include <linux/module.h>
>  #include <linux/of_platform.h>
> @@ -27,6 +28,8 @@ struct rpi_firmware {
>         struct mbox_chan *chan; /* The property channel. */
>         struct completion c;
>         u32 enabled;
> +
> +       struct kref consumers;
>  };
>
>  static DEFINE_MUTEX(transaction_lock);
> @@ -225,12 +228,27 @@ static void rpi_register_clk_driver(struct device *dev)
>                                                 -1, NULL, 0);
>  }
>
> +static void rpi_firmware_delete(struct kref *kref)
> +{
> +       struct rpi_firmware *fw = container_of(kref, struct rpi_firmware,
> +                                              consumers);
> +
> +       mbox_free_channel(fw->chan);
> +       kfree(fw);
> +}
> +
> +void rpi_firmware_put(struct rpi_firmware *fw)
> +{
> +       kref_put(&fw->consumers, rpi_firmware_delete);
> +}
> +EXPORT_SYMBOL_GPL(rpi_firmware_put);
> +
>  static int rpi_firmware_probe(struct platform_device *pdev)
>  {
>         struct device *dev = &pdev->dev;
>         struct rpi_firmware *fw;
>
> -       fw = devm_kzalloc(dev, sizeof(*fw), GFP_KERNEL);

One nit from my side: maybe add a comment here saying that you really
want to use non-managed kzalloc() because you're going to get people
blindly converting it to devm_kzalloc() very soon.

Bartosz

> +       fw = kzalloc(sizeof(*fw), GFP_KERNEL);
>         if (!fw)
>                 return -ENOMEM;
>
> @@ -247,6 +265,7 @@ static int rpi_firmware_probe(struct platform_device *pdev)
>         }
>
>         init_completion(&fw->c);
> +       kref_init(&fw->consumers);
>
>         platform_set_drvdata(pdev, fw);
>
> @@ -275,25 +294,35 @@ static int rpi_firmware_remove(struct platform_device *pdev)
>         rpi_hwmon = NULL;
>         platform_device_unregister(rpi_clk);
>         rpi_clk = NULL;
> -       mbox_free_channel(fw->chan);
> +
> +       rpi_firmware_put(fw);
>
>         return 0;
>  }
>
>  /**
> - * rpi_firmware_get - Get pointer to rpi_firmware structure.
>   * @firmware_node:    Pointer to the firmware Device Tree node.
>   *
> + * The reference to rpi_firmware has to be released with rpi_firmware_put().
> + *
>   * Returns NULL is the firmware device is not ready.
>   */
>  struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node)
>  {
>         struct platform_device *pdev = of_find_device_by_node(firmware_node);
> +       struct rpi_firmware *fw;
>
>         if (!pdev)
>                 return NULL;
>
> -       return platform_get_drvdata(pdev);
> +       fw = platform_get_drvdata(pdev);
> +       if (!fw)
> +               return NULL;
> +
> +       if (!kref_get_unless_zero(&fw->consumers))
> +               return NULL;
> +
> +       return fw;
>  }
>  EXPORT_SYMBOL_GPL(rpi_firmware_get);
>
> diff --git a/include/soc/bcm2835/raspberrypi-firmware.h b/include/soc/bcm2835/raspberrypi-firmware.h
> index cc9cdbc66403..fdfef7fe40df 100644
> --- a/include/soc/bcm2835/raspberrypi-firmware.h
> +++ b/include/soc/bcm2835/raspberrypi-firmware.h
> @@ -140,6 +140,7 @@ int rpi_firmware_property(struct rpi_firmware *fw,
>                           u32 tag, void *data, size_t len);
>  int rpi_firmware_property_list(struct rpi_firmware *fw,
>                                void *data, size_t tag_size);
> +void rpi_firmware_put(struct rpi_firmware *fw);
>  struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node);
>  #else
>  static inline int rpi_firmware_property(struct rpi_firmware *fw, u32 tag,
> @@ -154,6 +155,7 @@ static inline int rpi_firmware_property_list(struct rpi_firmware *fw,
>         return -ENOSYS;
>  }
>
> +static inline void rpi_firmware_put(struct rpi_firmware *fw) { }
>  static inline struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node)
>  {
>         return NULL;
> --
> 2.29.2
>