Re: [PATCH] gpio: don't use same lockdep class for all devm_gpiochip_add_data users

[Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>]

On Fri, Jul 31, 2020 at 2:39 PM Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx> wrote:
>
> Commit 959bc7b22bd2 ("gpio: Automatically add lockdep keys") documents
> in its commits message its intention to "create a unique class key for
> each driver".
>
> It does so by having gpiochip_add_data add in-place the definition of
> two static lockdep classes for LOCKDEP use. That way, every caller of
> the macro adds their gpiochip with unique lockdep classes.
>
> There are many indirect callers of gpiochip_add_data, however, via
> use of devm_gpiochip_add_data. devm_gpiochip_add_data has external
> linkage and all its users will share the same lockdep classes, which
> probably is not intended.
>
> Fix this by replicating the gpio_chip_add_data statics-in-macro for
> the devm_ version as well.
>
> Fixes: 959bc7b22bd2 ("gpio: Automatically add lockdep keys")
> Signed-off-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx>
> ---
> This doesn't fix any particular problem I ran into, but the code
> looked buggy, at least to my lockdep-user-not-developer eyes.
> ---
>  drivers/gpio/gpiolib-devres.c | 13 ++++++++-----
>  include/linux/gpio/driver.h   | 13 +++++++++++--
>  2 files changed, 19 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib-devres.c b/drivers/gpio/gpiolib-devres.c
> index 5c91c4365da1..7dbce4c4ebdf 100644
> --- a/drivers/gpio/gpiolib-devres.c
> +++ b/drivers/gpio/gpiolib-devres.c
> @@ -487,10 +487,12 @@ static void devm_gpio_chip_release(struct device *dev, void *res)
>  }
>
>  /**
> - * devm_gpiochip_add_data() - Resource managed gpiochip_add_data()
> + * devm_gpiochip_add_data_with_key() - Resource managed gpiochip_add_data_with_key()
>   * @dev: pointer to the device that gpio_chip belongs to.
>   * @gc: the GPIO chip to register
>   * @data: driver-private data associated with this chip
> + * @lock_key: lockdep class for IRQ lock
> + * @request_key: lockdep class for IRQ request
>   *
>   * Context: potentially before irqs will work
>   *
> @@ -501,8 +503,9 @@ static void devm_gpio_chip_release(struct device *dev, void *res)
>   * gc->base is invalid or already associated with a different chip.
>   * Otherwise it returns zero as a success code.
>   */
> -int devm_gpiochip_add_data(struct device *dev, struct gpio_chip *gc,
> -                          void *data)
> +int devm_gpiochip_add_data_with_key(struct device *dev, struct gpio_chip *gc, void *data,
> +                                   struct lock_class_key *lock_key,
> +                                   struct lock_class_key *request_key)
>  {
>         struct gpio_chip **ptr;
>         int ret;
> @@ -512,7 +515,7 @@ int devm_gpiochip_add_data(struct device *dev, struct gpio_chip *gc,
>         if (!ptr)
>                 return -ENOMEM;
>
> -       ret = gpiochip_add_data(gc, data);
> +       ret = gpiochip_add_data_with_key(gc, data, lock_key, request_key);
>         if (ret < 0) {
>                 devres_free(ptr);
>                 return ret;
> @@ -523,4 +526,4 @@ int devm_gpiochip_add_data(struct device *dev, struct gpio_chip *gc,
>
>         return 0;
>  }
> -EXPORT_SYMBOL_GPL(devm_gpiochip_add_data);
> +EXPORT_SYMBOL_GPL(devm_gpiochip_add_data_with_key);
> diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
> index c4f272af7af5..e6217d8e2e9f 100644
> --- a/include/linux/gpio/driver.h
> +++ b/include/linux/gpio/driver.h
> @@ -509,8 +509,16 @@ extern int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
>                 gpiochip_add_data_with_key(gc, data, &lock_key, \
>                                            &request_key);         \
>         })
> +#define devm_gpiochip_add_data(dev, gc, data) ({ \
> +               static struct lock_class_key lock_key;  \
> +               static struct lock_class_key request_key;         \
> +               devm_gpiochip_add_data_with_key(dev, gc, data, &lock_key, \
> +                                          &request_key);         \
> +       })
>  #else
>  #define gpiochip_add_data(gc, data) gpiochip_add_data_with_key(gc, data, NULL, NULL)
> +#define devm_gpiochip_add_data(dev, gc, data) \
> +       devm_gpiochip_add_data_with_key(dev, gc, data, NULL, NULL)
>  #endif /* CONFIG_LOCKDEP */
>
>  static inline int gpiochip_add(struct gpio_chip *gc)
> @@ -518,8 +526,9 @@ static inline int gpiochip_add(struct gpio_chip *gc)
>         return gpiochip_add_data(gc, NULL);
>  }
>  extern void gpiochip_remove(struct gpio_chip *gc);
> -extern int devm_gpiochip_add_data(struct device *dev, struct gpio_chip *gc,
> -                                 void *data);
> +extern int devm_gpiochip_add_data_with_key(struct device *dev, struct gpio_chip *gc, void *data,
> +                                          struct lock_class_key *lock_key,
> +                                          struct lock_class_key *request_key);
>
>  extern struct gpio_chip *gpiochip_find(void *data,
>                               int (*match)(struct gpio_chip *gc, void *data));
> --
> 2.27.0
>

Looks good to me and the previous code indeed looks buggy.

Reviewed-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>