* @timestamp: Timestamp when the fence was signaled.
* @status: Optional, only valid if < 0, must be set before calling
* fence_signal, indicates that the fence has completed with an error.
- * @child_list: list of children fences
- * @active_list: list of active fences
*
* the flags member must be manipulated and read using the appropriate
* atomic ops (bit_*), so taking the spinlock will not be needed most