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Revert "drm/virtio: Use dma_buf from GEM object instance"

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This reverts commit 415cb45895.

The dma_buf field in struct drm_gem_object is not stable over the
object instance's lifetime. The field becomes NULL when user space
releases the final GEM handle on the buffer object. This resulted
in a NULL-pointer deref.

Workarounds in commit 5307dce878 ("drm/gem: Acquire references on
GEM handles for framebuffers") and commit f6bfc9afc7 ("drm/framebuffer:
Acquire internal references on GEM handles") only solved the problem
partially. They especially don't work for buffer objects without a DRM
framebuffer associated.

Hence, this revert to going back to using .import_attach->dmabuf.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Zack Rusin <zack.rusin@broadcom.com>
Link: https://lore.kernel.org/r/20250715155934.150656-3-tzimmermann@suse.de
This commit is contained in:
Thomas Zimmermann
2025-07-15 17:58:11 +02:00
parent 15f77764e9
commit 0ecfb8ddb9
1 changed files with 3 additions and 2 deletions
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5
drivers/gpu/drm/virtio/virtgpu_prime.c
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@@ -204,15 +204,16 @@ static void virtgpu_dma_buf_free_obj(struct drm_gem_object *obj)
{
struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(obj);
struct virtio_gpu_device *vgdev = obj->dev->dev_private;
struct dma_buf_attachment *attach = obj->import_attach;
if (drm_gem_is_imported(obj)) {
struct dma_buf *dmabuf = obj->dma_buf;
struct dma_buf *dmabuf = attach->dmabuf;
dma_resv_lock(dmabuf->resv, NULL);
virtgpu_dma_buf_unmap(bo);
dma_resv_unlock(dmabuf->resv);
dma_buf_detach(dmabuf, obj->import_attach);
dma_buf_detach(dmabuf, attach);
dma_buf_put(dmabuf);
}