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

commit ed7d78b2da32198ca4c70172e3b63c6b3e2c570b upstream.

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

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
index 9e190db6cc3702fca890560b02f42f78bfe6fd89..17a4107639b2abc7fd7896e1ec239aad057728b4 100644 (file)
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
@@ -653,7 +653,8 @@ 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);
 }