[PATCH] drm/managed: Define drmm_mutex_init() as a macro to fix lockdep

[Matthew Auld]

On Fri, 19 May 2023 at 09:55, Boris Brezillon
<boris.brezillon at collabora.com> wrote:
>
> drmm_mutex_init() needs to be defined as a macro if we want
> lockdep to classify locks properly. If we don't do that, all locks
> will be considered as belonging to the same lock class, leading to
> false positive deadlock reports.
>
> Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>
> Reported-by: Sarah Walker <sarah.walker at imgtec.com>

Yeah, we also encountered the same issue. Patch is here:
https://patchwork.freedesktop.org/patch/537605/?series=117891&rev=2

> ---
>  drivers/gpu/drm/drm_managed.c | 26 --------------------------
>  include/drm/drm_managed.h     | 30 +++++++++++++++++++++++++++++-
>  2 files changed, 29 insertions(+), 27 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_managed.c b/drivers/gpu/drm/drm_managed.c
> index 4cf214de50c4..71c49819a7a2 100644
> --- a/drivers/gpu/drm/drm_managed.c
> +++ b/drivers/gpu/drm/drm_managed.c
> @@ -263,29 +263,3 @@ void drmm_kfree(struct drm_device *dev, void *data)
>         free_dr(dr_match);
>  }
>  EXPORT_SYMBOL(drmm_kfree);
> -
> -static void drmm_mutex_release(struct drm_device *dev, void *res)
> -{
> -       struct mutex *lock = res;
> -
> -       mutex_destroy(lock);
> -}
> -
> -/**
> - * drmm_mutex_init - &drm_device-managed mutex_init()
> - * @dev: DRM device
> - * @lock: lock to be initialized
> - *
> - * Returns:
> - * 0 on success, or a negative errno code otherwise.
> - *
> - * This is a &drm_device-managed version of mutex_init(). The initialized
> - * lock is automatically destroyed on the final drm_dev_put().
> - */
> -int drmm_mutex_init(struct drm_device *dev, struct mutex *lock)
> -{
> -       mutex_init(lock);
> -
> -       return drmm_add_action_or_reset(dev, drmm_mutex_release, lock);
> -}
> -EXPORT_SYMBOL(drmm_mutex_init);
> diff --git a/include/drm/drm_managed.h b/include/drm/drm_managed.h
> index 359883942612..87ffb92a16ba 100644
> --- a/include/drm/drm_managed.h
> +++ b/include/drm/drm_managed.h
> @@ -105,6 +105,34 @@ char *drmm_kstrdup(struct drm_device *dev, const char *s, gfp_t gfp);
>
>  void drmm_kfree(struct drm_device *dev, void *data);
>
> -int drmm_mutex_init(struct drm_device *dev, struct mutex *lock);
> +/* Private function, don't use. */
> +static inline void __drmm_mutex_release(struct drm_device *dev, void *res)
> +{
> +       struct mutex *lock = res;
> +
> +       mutex_destroy(lock);
> +}
> +
> +/**
> + * drmm_mutex_init - &drm_device-managed mutex_init()
> + * @dev: DRM device
> + * @lock: lock to be initialized
> + *
> + * Returns:
> + * 0 on success, or a negative errno code otherwise.
> + *
> + * This is a &drm_device-managed version of mutex_init(). The initialized
> + * lock is automatically destroyed on the final drm_dev_put().
> + *
> + * This needs to be defined as a macro to let lockdep classify locks
> + * properly. If we don't do that, all locks will be considered as
> + * belonging to the same lock class, leading to false positive lockdep
> + * reports.
> + */
> +#define drmm_mutex_init(dev, lock) \
> +       ({\
> +               mutex_init(lock); \
> +               drmm_add_action_or_reset(dev, __drmm_mutex_release, lock); \
> +       })
>
>  #endif
> --
> 2.40.1
>