[PATCH v2 7/7] Revert "drm/gem-dma: Use dma_buf from GEM object instance"

[Thomas Zimmermann]

This reverts commit e8afa1557f4f963c9a511bd2c6074a941c308685.

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/drm_gem_dma_helper.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_gem_dma_helper.c b/drivers/gpu/drm/drm_gem_dma_helper.c
index b7f033d4352a..4f0320df858f 100644
--- a/drivers/gpu/drm/drm_gem_dma_helper.c
+++ b/drivers/gpu/drm/drm_gem_dma_helper.c
@@ -230,7 +230,7 @@ void drm_gem_dma_free(struct drm_gem_dma_object *dma_obj)
 
 	if (drm_gem_is_imported(gem_obj)) {
 		if (dma_obj->vaddr)
-			dma_buf_vunmap_unlocked(gem_obj->dma_buf, &map);
+			dma_buf_vunmap_unlocked(gem_obj->import_attach->dmabuf, &map);
 		drm_prime_gem_destroy(gem_obj, dma_obj->sgt);
 	} else if (dma_obj->vaddr) {
 		if (dma_obj->map_noncoherent)
-- 
2.50.0