Re: [PATCH 01/10] drm/exec: Add helper to bypass IGNORE_DUPLICATES flag

["Christian König" <christian.koenig@amd.com>]

On 7/3/26 18:31, Natalie Vock wrote:
> TTM is about to switch to drm_exec for locking objects
> in the LRU list. When we're done processing the object, we want to
> unlock it only if the caller doesn't already hold that lock. If
> DRM_EXEC_IGNORE_DUPLICATES is set on the exec object (which callers may
> require for unrelated reasons), we have no way of knowing whether the
> lock is already held.
> 
> To remedy this, add a separate helper that forcefully bypasses the
> IGNORE_DUPLICATES flag for only a single locking operation.
> 
> Signed-off-by: Natalie Vock <natalie.vock@gmx.de>
> ---
>  drivers/gpu/drm/drm_exec.c | 52 ++++++++++++++++++++++++++++++++++------------
>  include/drm/drm_exec.h     |  2 ++
>  2 files changed, 41 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_exec.c b/drivers/gpu/drm/drm_exec.c
> index 7988f5e7d56a3..91de6b4d29df8 100644
> --- a/drivers/gpu/drm/drm_exec.c
> +++ b/drivers/gpu/drm/drm_exec.c
> @@ -190,18 +190,9 @@ static int drm_exec_lock_contended(struct drm_exec *exec)
>  	return ret;
>  }
>  
> -/**
> - * drm_exec_lock_obj - lock a GEM object for use
> - * @exec: the drm_exec object with the state
> - * @obj: the GEM object to lock
> - *
> - * Lock a GEM object for use and grab a reference to it.
> - *
> - * Returns: -EDEADLK if a contention is detected, -EALREADY when object is
> - * already locked (can be suppressed by setting the DRM_EXEC_IGNORE_DUPLICATES
> - * flag), -ENOMEM when memory allocation failed and zero for success.
> - */
> -int drm_exec_lock_obj(struct drm_exec *exec, struct drm_gem_object *obj)
> +static int __drm_exec_lock_obj(struct drm_exec *exec,
> +			       struct drm_gem_object *obj,
> +			       bool always_report_duplicates)

Rename the new parameter to ignore_duplicates.

>  {
>  	int ret;
>  
> @@ -226,7 +217,7 @@ int drm_exec_lock_obj(struct drm_exec *exec, struct drm_gem_object *obj)
>  		return -EDEADLK;
>  	}
>  
> -	if (unlikely(ret == -EALREADY) &&
> +	if (unlikely(ret == -EALREADY) && !always_report_duplicates &&
>  	    exec->flags & DRM_EXEC_IGNORE_DUPLICATES)
>  		return 0;
>  
> @@ -243,8 +234,43 @@ int drm_exec_lock_obj(struct drm_exec *exec, struct drm_gem_object *obj)
>  	dma_resv_unlock(obj->resv);
>  	return ret;
>  }
> +
> +/**
> + * drm_exec_lock_obj - lock a GEM object for use
> + * @exec: the drm_exec object with the state
> + * @obj: the GEM object to lock
> + *
> + * Lock a GEM object for use and grab a reference to it.
> + *
> + * Returns: -EDEADLK if a contention is detected, -EALREADY when object is
> + * already locked (can be suppressed by setting the DRM_EXEC_IGNORE_DUPLICATES
> + * flag), -ENOMEM when memory allocation failed and zero for success.
> + */
> +int drm_exec_lock_obj(struct drm_exec *exec, struct drm_gem_object *obj)
> +{
> +	return __drm_exec_lock_obj(exec, obj, false);

And then use "exec->flags & DRM_EXEC_IGNORE_DUPLICATES" here.

> +}
>  EXPORT_SYMBOL(drm_exec_lock_obj);
>  
> +/**
> + * drm_exec_lock_obj_report_dup - lock a GEM object for use, but always report duplicates
> + * @exec: the drm_exec object with the state
> + * @obj: the GEM object to lock
> + *
> + * Like drm_exec_lock_obj, lock a GEM object for use and grab a reference to it.
> + * Unlike drm_exec_lock_obj, DRM_EXEC_IGNORE_DUPLICATES is ignored and duplicates are
> + * always reported.
> + *
> + * Returns: -EDEADLK if a contention is detected, -EALREADY when object is
> + * already locked, -ENOMEM when memory allocation failed and zero for success.
> + */
> +int drm_exec_lock_obj_report_dup(struct drm_exec *exec,
> +				 struct drm_gem_object *obj)
> +{
> +	return __drm_exec_lock_obj(exec, obj, false);

BTW That here is buggy, it should have been true.

Apart from that looks good to me,
Christian.

> +}
> +EXPORT_SYMBOL(drm_exec_lock_obj_report_dup);
> +
>  /**
>   * drm_exec_unlock_obj - unlock a GEM object in this exec context
>   * @exec: the drm_exec object with the state
> diff --git a/include/drm/drm_exec.h b/include/drm/drm_exec.h
> index 8725ba92ff916..ff80dd2b72240 100644
> --- a/include/drm/drm_exec.h
> +++ b/include/drm/drm_exec.h
> @@ -176,6 +176,8 @@ void drm_exec_init(struct drm_exec *exec, u32 flags, unsigned nr);
>  void drm_exec_fini(struct drm_exec *exec);
>  bool drm_exec_cleanup(struct drm_exec *exec);
>  int drm_exec_lock_obj(struct drm_exec *exec, struct drm_gem_object *obj);
> +int drm_exec_lock_obj_report_dup(struct drm_exec *exec,
> +				 struct drm_gem_object *obj);
>  void drm_exec_unlock_obj(struct drm_exec *exec, struct drm_gem_object *obj);
>  int drm_exec_prepare_obj(struct drm_exec *exec, struct drm_gem_object *obj,
>  			 unsigned int num_fences);
>