> On 29 Aug 2025, at 19:35, Lyude Paul <lyude@redhat.com> wrote:
>
> At the moment the way that freeing gem shmem objects is not ideal for rust
This does not read very well IMHO.
> bindings. drm_gem_shmem_free() releases all of the associated memory with a
> gem shmem object with kfree(), which means that for us to correctly release
> a gem shmem object in rust we have to manually drop all of the contents of
> our gem object structure in-place by hand before finally calling
> drm_gem_shmem_free() to release the shmem resources and the allocation for
> the gem object.
>
> Since the only reason this is an issue is because of drm_gem_shmem_free()
> calling kfree(), we can fix this by splitting drm_gem_shmem_free() out into
> itself and drm_gem_shmem_release(), where drm_gem_shmem_release() releases
> the various gem shmem resources without freeing the structure itself. With
> this, we can safely re-acquire the KBox for the gem object's memory
> allocation and let rust handle cleaning up all of the other struct members
> automatically.
>
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> ---
> drivers/gpu/drm/drm_gem_shmem_helper.c | 23 ++++++++++++++++++-----
> include/drm/drm_gem_shmem_helper.h | 1 +
> 2 files changed, 19 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index b20a7b75c7228..50594cf8e17cc 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -175,13 +175,13 @@ struct drm_gem_shmem_object *drm_gem_shmem_create_with_mnt(struct drm_device *de
> EXPORT_SYMBOL_GPL(drm_gem_shmem_create_with_mnt);
>
> /**
> - * drm_gem_shmem_free - Free resources associated with a shmem GEM object
> - * @shmem: shmem GEM object to free
> + * drm_gem_shmem_release - Release resources associated with a shmem GEM object.
> + * @shmem: shmem GEM object
> *
> - * This function cleans up the GEM object state and frees the memory used to
> - * store the object itself.
> + * This function cleans up the GEM object state, but does not free the memory used to store the
> + * object itself. This function is meant to be a dedicated helper for the Rust GEM bindings.
> */
> -void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
> +void drm_gem_shmem_release(struct drm_gem_shmem_object *shmem)
> {
> struct drm_gem_object *obj = &shmem->base;
>
> @@ -208,6 +208,19 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
> }
>
> drm_gem_object_release(obj);
> +}
> +EXPORT_SYMBOL_GPL(drm_gem_shmem_release);
> +
> +/**
> + * drm_gem_shmem_free - Free resources associated with a shmem GEM object
> + * @shmem: shmem GEM object to free
> + *
> + * This function cleans up the GEM object state and frees the memory used to
> + * store the object itself.
> + */
> +void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
> +{
> + drm_gem_shmem_release(shmem);
> kfree(shmem);
> }
> EXPORT_SYMBOL_GPL(drm_gem_shmem_free);
> diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
> index 235dc33127b9a..589f7bfe7506e 100644
> --- a/include/drm/drm_gem_shmem_helper.h
> +++ b/include/drm/drm_gem_shmem_helper.h
> @@ -112,6 +112,7 @@ struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t
> struct drm_gem_shmem_object *drm_gem_shmem_create_with_mnt(struct drm_device *dev,
> size_t size,
> struct vfsmount *gemfs);
> +void drm_gem_shmem_release(struct drm_gem_shmem_object *shmem);
> void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem);
>
> void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem);
> --
> 2.50.0
>
>
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>