[PATCH] Revert "drm/tegra: Use dma_buf from GEM object instance"

[Simona Vetter]

On Tue, Jul 15, 2025 at 10:45:39AM +0200, Thomas Zimmermann wrote:
> This reverts commit 482c7e296edc0f594e8869a789a40be53c49bd6a.
> 
> 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 5307dce878d4 ("drm/gem: Acquire references on
> GEM handles for framebuffers") and commit f6bfc9afc751 ("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 at suse.de>

Reviewed-by: Simona Vetter <simona.vetter at ffwll.ch>

> ---
>  drivers/gpu/drm/tegra/gem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
> index 41a285ec889f..8ede07fb7a21 100644
> --- a/drivers/gpu/drm/tegra/gem.c
> +++ b/drivers/gpu/drm/tegra/gem.c
> @@ -526,7 +526,7 @@ void tegra_bo_free_object(struct drm_gem_object *gem)
>  		if (drm_gem_is_imported(gem)) {
>  			dma_buf_unmap_attachment_unlocked(gem->import_attach, bo->sgt,
>  							  DMA_TO_DEVICE);
> -			dma_buf_detach(gem->dma_buf, gem->import_attach);
> +			dma_buf_detach(gem->import_attach->dmabuf, gem->import_attach);
>  		}
>  	}
>  
> -- 
> 2.50.0
> 

-- 
Simona Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch