The commit "drm/vmwgfx: Fix up user_dmabuf refcounting", while fixing a
kernel crash introduced a NULL pointer dereference on older hardware.
Fix this.

Cc: <[email protected]>
Signed-off-by: Thomas Hellstrom <[email protected]>
Reviewed-by: Sinclair Yeh <[email protected]>
Reviewed-by: Brian Paul <[email protected]>
---
 drivers/gpu/drm/vmwgfx/vmwgfx_surface.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c 
b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
index 64b5040..03f63c7 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
@@ -657,7 +657,8 @@ static void vmw_user_surface_base_release(struct 
ttm_base_object **p_base)
        struct vmw_resource *res = &user_srf->srf.res;
 
        *p_base = NULL;
-       ttm_base_object_unref(&user_srf->backup_base);
+       if (user_srf->backup_base)
+               ttm_base_object_unref(&user_srf->backup_base);
        vmw_resource_unreference(&res);
 }
 
-- 
2.1.0

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