* node being deleted may be visited once or not at all. Other nodes
* will be visited once.)
*
+ * - If the cmap is changing, it is not safe to quiesce while iterating.
+ * Even if the changes are done by the same thread that's performing the
+ * iteration (Corollary: it is not safe to call cmap_remove() and quiesce
+ * in the loop body).
+ *
*
* Example
* =======