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

[Thomas Zimmermann]

Hi

Am 15.04.25 um 11:39 schrieb 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.

I understand that it's not ideal, but testing for import_attach to be 
set is what we currently do throughout drivers. Putting this behind an 
interface is already a step forward.

>
>> 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.

Did you look at the discussion at the Closes tag? Where else could 
dma-buf be cleared?

Best regards
Thomas

>
> 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

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)