[PATCH v2 2/7] Revert "drm/vmwgfx: Use dma_buf from GEM object instance"

[Thomas Zimmermann]

This reverts commit aec8a40228acb385d60feec59b54573d307e60f3.

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 <tzimmerm...@suse.de>
Reviewed-by: Simona Vetter <simona.vet...@ffwll.ch>
---
 drivers/gpu/drm/vmwgfx/vmwgfx_gem.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c 
b/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c
index 7057d852951b..eedf1fe60be7 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c
@@ -85,10 +85,10 @@ static int vmw_gem_vmap(struct drm_gem_object *obj, struct 
iosys_map *map)
        int ret;
 
        if (drm_gem_is_imported(obj)) {
-               ret = dma_buf_vmap(obj->dma_buf, map);
+               ret = dma_buf_vmap(obj->import_attach->dmabuf, map);
                if (!ret) {
                        if (drm_WARN_ON(obj->dev, map->is_iomem)) {
-                               dma_buf_vunmap(obj->dma_buf, map);
+                               dma_buf_vunmap(obj->import_attach->dmabuf, map);
                                return -EIO;
                        }
                }
@@ -102,7 +102,7 @@ static int vmw_gem_vmap(struct drm_gem_object *obj, struct 
iosys_map *map)
 static void vmw_gem_vunmap(struct drm_gem_object *obj, struct iosys_map *map)
 {
        if (drm_gem_is_imported(obj))
-               dma_buf_vunmap(obj->dma_buf, map);
+               dma_buf_vunmap(obj->import_attach->dmabuf, map);
        else
                drm_gem_ttm_vunmap(obj, map);
 }
-- 
2.50.0