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

Bartosz Golaszewski
2020-12-03T08:06:24Z

On Mon, Nov 23, 2020 at 7:38 PM Nicolas Saenz Julienne
<nsaenzjulienne@suse.de> 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@pengutronix.de>
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> ---
>
> 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
>