drm/vmwgfx: Fix kernel NULL pointer dereference on older hardware

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: <stable@vger.kernel.org>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
index 64b50409fa07..03f63c749c02 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);
 }