[PATCH v5 1/7] drm: fix drmm_mutex_init()

[Thomas Zimmermann]

Hi

Am 17.05.23 um 17:22 schrieb Matthew Auld:
> In mutex_init() lockdep seems to identify a lock by defining a static
> key for each lock class. However if we wrap the whole thing in a
> function the static key will be the same for everything calling that
> function, which looks to be the case for drmm_mutex_init(). This then
> results in impossible lockdep splats since lockdep thinks completely
> unrelated locks are the same lock class. The other issue is that when
> looking at splats we lose the actual lock name, where instead of seeing
> something like xe->mem_access.lock for the name, we just see something
> generic like lock#8.
> 
> Attempt to fix this by converting drmm_mutex_init() into a macro, which
> should ensure that mutex_init() behaves as expected.

If that's what is required, then OK. But even with your commit mesage, I 
find it entirely non-obvious what the problem is. Isn't there a way to 
annotate drmm_mutex_init() so that lockdep treats it like a regular 
mutex_init()?

Best regards
Thomas

> 
> Reported-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> Fixes: e13f13e039dc ("drm: Add DRM-managed mutex_init()")
> Cc: Thomas Zimmermann <tzimmermann at suse.de>
> Cc: Jocelyn Falempe <jfalempe at redhat.com>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Cc: dri-devel at lists.freedesktop.org
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> ---
>   drivers/gpu/drm/drm_managed.c | 26 --------------------------
>   include/drm/drm_managed.h     | 23 ++++++++++++++++++++++-
>   2 files changed, 22 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..01f977e91933 100644
> --- a/include/drm/drm_managed.h
> +++ b/include/drm/drm_managed.h
> @@ -105,6 +105,27 @@ 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);
> +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().
> + */
> +#define drmm_mutex_init(dev, lock) ({					     \
> +	mutex_init(lock);						     \
> +	drmm_add_action_or_reset(dev, __drmm_mutex_release, lock);	     \
> +})									     \
>   
>   #endif

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)
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