linux-kernel - Re: [PATCH v3 08/14] drm/gem/shmem: Extract drm_gem_shmem_release() from drm_gem_shmem

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Message-Id: <A6150946-73B6-43AE-B12C-B0E692E9E3A5@collabora.com>
Date: Thu, 4 Sep 2025 10:35:05 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Lyude Paul <lyude@...hat.com>
Cc: dri-devel@...ts.freedesktop.org,
 rust-for-linux@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>,
 Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>,
 Miguel Ojeda <ojeda@...nel.org>,
 Alex Gaynor <alex.gaynor@...il.com>,
 Boqun Feng <boqun.feng@...il.com>,
 Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Benno Lossin <lossin@...nel.org>,
 Andreas Hindborg <a.hindborg@...nel.org>,
 Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>,
 Danilo Krummrich <dakr@...nel.org>
Subject: Re: [PATCH v3 08/14] drm/gem/shmem: Extract drm_gem_shmem_release()
 from drm_gem_shmem_free()



> On 29 Aug 2025, at 19:35, Lyude Paul <lyude@...hat.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@...hat.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@...labora.com>