[PATCH v3 3/7] Revert "drm/etnaviv: Use dma_buf from GEM object instance"

[Thomas Zimmermann]

This reverts commit e91eb3ae415472b28211d7fed07fa283845b311e.

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>
Acked-by: Christian König <christian.koenig at amd.com>
---
 drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c b/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
index 917ad527c961..40a50c60dfff 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
@@ -65,7 +65,7 @@ static void etnaviv_gem_prime_release(struct etnaviv_gem_object *etnaviv_obj)
 	struct iosys_map map = IOSYS_MAP_INIT_VADDR(etnaviv_obj->vaddr);
 
 	if (etnaviv_obj->vaddr)
-		dma_buf_vunmap_unlocked(etnaviv_obj->base.dma_buf, &map);
+		dma_buf_vunmap_unlocked(etnaviv_obj->base.import_attach->dmabuf, &map);
 
 	/* Don't drop the pages for imported dmabuf, as they are not
 	 * ours, just free the array we allocated:
@@ -82,7 +82,7 @@ static void *etnaviv_gem_prime_vmap_impl(struct etnaviv_gem_object *etnaviv_obj)
 
 	lockdep_assert_held(&etnaviv_obj->lock);
 
-	ret = dma_buf_vmap(etnaviv_obj->base.dma_buf, &map);
+	ret = dma_buf_vmap(etnaviv_obj->base.import_attach->dmabuf, &map);
 	if (ret)
 		return NULL;
 	return map.vaddr;
-- 
2.50.0