[PATCH v2] drm/gem: Internally test import_attach for imported objects

[Thomas Zimmermann <tzimmermann@suse.de>]

Test struct drm_gem_object.import_attach.dmabuf to detect imported
objects. Warn if the stored state is inconsistent.

During object clenaup, the dma_buf field might be NULL. Testing it in
an object's free callback then incorrectly does a cleanup as for native
objects. Happens for calls to drm_mode_destroy_dumb_ioctl() that
clears the dma_buf field in drm_gem_object_exported_dma_buf_free().

v2:
- use import_attach.dmabuf instead of dma_buf (Christian)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: b57aa47d39e9 ("drm/gem: Test for imported GEM buffers with helper")
Reported-by: Andy Yan <andyshrk@163.com>
Closes: https://lore.kernel.org/dri-devel/38d09d34.4354.196379aa560.Coremail.andyshrk@163.com/
Tested-by: Andy Yan <andyshrk@163.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Anusha Srivatsa <asrivats@redhat.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: David Airlie <airlied@gmail.com>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
---
 include/drm/drm_gem.h | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index 9b71f7a9f3f8..464b9c7feec0 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -579,6 +579,21 @@ static inline bool drm_gem_object_is_shared_for_memory_stats(struct drm_gem_obje
 	return (obj->handle_count > 1) || obj->dma_buf;
 }
 
+/**
+ * drm_gem_owns_dma_buf() - Tests if GEM object backs a DMA-buffer object
+ * @obj: the GEM object
+ * @obj: the DMA buffer
+ *
+ * Returns:
+ * True if the DMA buffer refers to the GEM object's buffer.
+ */
+static inline bool drm_gem_owns_dma_buf(const struct drm_gem_object *obj,
+					const struct dma_buf *dma_buf)
+{
+	/* The dma-buf's priv field points to the original GEM object. */
+	return dma_buf->priv == obj;
+}
+
 /**
  * drm_gem_is_imported() - Tests if GEM object's buffer has been imported
  * @obj: the GEM object
@@ -588,8 +603,15 @@ static inline bool drm_gem_object_is_shared_for_memory_stats(struct drm_gem_obje
  */
 static inline bool drm_gem_is_imported(const struct drm_gem_object *obj)
 {
-	/* The dma-buf's priv field points to the original GEM object. */
-	return obj->dma_buf && (obj->dma_buf->priv != obj);
+	const struct dma_buf *dma_buf = NULL;
+
+	if (!obj->import_attach)
+		return false;
+
+	dma_buf = obj->import_attach->dmabuf;
+
+	/* Warn if we somehow reimported our own buffer. */
+	return !drm_WARN_ON_ONCE(obj->dev, !dma_buf || drm_gem_owns_dma_buf(obj, dma_buf));
 }
 
 #ifdef CONFIG_LOCKDEP
-- 
2.49.0