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

[Christian König]

Am 15.04.25 um 11:20 schrieb Thomas Zimmermann:
> Test struct drm_gem_object.import_attach to detect imported objects
> during cleanup. At that point, the imported DMA buffer might have
> already been released and the dma_buf field is NULL. The object's
> free callback then does a cleanup as for native objects.

I don't think that this is a good idea.

The DMA-buf is separately reference counted through the import attachment.

> Happens for calls to drm_mode_destroy_dumb_ioctl() that eventually
> clear the dma_buf field in drm_gem_object_exported_dma_buf_free().

That is for exported DMA-buf and should *NEVER* be used for imported ones.

Regards,
Christian.

>
> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> Fixes: b57aa47d39e9 ("drm/gem: Test for imported GEM buffers with helper")
> Reported-by: Andy Yan <andyshrk at 163.com>
> Closes: https://lore.kernel.org/dri-devel/38d09d34.4354.196379aa560.Coremail.andyshrk@163.com/
> Tested-by: Andy Yan <andyshrk at 163.com>
> Cc: Thomas Zimmermann <tzimmermann at suse.de>
> Cc: Anusha Srivatsa <asrivats at redhat.com>
> Cc: Christian König <christian.koenig at amd.com>
> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Cc: Maxime Ripard <mripard at kernel.org>
> Cc: David Airlie <airlied at gmail.com>
> Cc: Simona Vetter <simona at ffwll.ch>
> Cc: Sumit Semwal <sumit.semwal at linaro.org>
> Cc: "Christian König" <christian.koenig at amd.com>
> Cc: dri-devel at lists.freedesktop.org
> Cc: linux-media at vger.kernel.org
> Cc: linaro-mm-sig at lists.linaro.org
> ---
>  include/drm/drm_gem.h | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
> index 9b71f7a9f3f8..f09b8afcf86d 100644
> --- a/include/drm/drm_gem.h
> +++ b/include/drm/drm_gem.h
> @@ -589,7 +589,13 @@ 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);
> +	return (obj->dma_buf && (obj->dma_buf->priv != obj)) ||
> +	       /*
> +		* TODO: During object release, the dma-buf might already
> +		*       be gone. For now keep testing import_attach, but
> +		*       this should be removed at some point.
> +		*/
> +	       obj->import_attach;
>  }
>  
>  #ifdef CONFIG_LOCKDEP