linux-kernel - [PATCH v2 04/12] drm/gem/shmem: Extract drm_gem_shmem_release() from drm_gem_shmem

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Message-ID: <20250521204654.1610607-5-lyude@redhat.com>
Date: Wed, 21 May 2025 16:29:11 -0400
From: Lyude Paul <lyude@...hat.com>
To: dri-devel@...ts.freedesktop.org,
	rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: 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 <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>
Subject: [PATCH v2 04/12] drm/gem/shmem: Extract drm_gem_shmem_release() from drm_gem_shmem_free()

At the moment the way that freeing gem shmem objects is not ideal for rust
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 f3e88fb579b52..42652be37ba77 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;
 
@@ -207,6 +207,19 @@ 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 ea0785d1700a5..e009022b0bb48 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -101,6 +101,7 @@ 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(struct drm_gem_shmem_object *shmem);
-- 
2.49.0