+ /*
+ * Paired with the wmb in mempool_alloc(). The preceding read is
+ * for @element and the following @pool->curr_nr. This ensures
+ * that the visible value of @pool->curr_nr is from after the
+ * allocation of @element. This is necessary for fringe cases
+ * where @element was passed to this task without going through
+ * barriers.
+ *
+ * For example, assume @p is %NULL at the beginning and one task
+ * performs "p = mempool_alloc(...);" while another task is doing
+ * "while (!p) cpu_relax(); mempool_free(p, ...);". This function
+ * may end up using curr_nr value which is from before allocation
+ * of @p without the following rmb.
+ */
+ smp_rmb();
+
+ /*
+ * For correctness, we need a test which is guaranteed to trigger
+ * if curr_nr + #allocated == min_nr. Testing curr_nr < min_nr
+ * without locking achieves that and refilling as soon as possible
+ * is desirable.
+ *
+ * Because curr_nr visible here is always a value after the
+ * allocation of @element, any task which decremented curr_nr below
+ * min_nr is guaranteed to see curr_nr < min_nr unless curr_nr gets
+ * incremented to min_nr afterwards. If curr_nr gets incremented
+ * to min_nr after the allocation of @element, the elements
+ * allocated after that are subject to the same guarantee.
+ *
+ * Waiters happen iff curr_nr is 0 and the above guarantee also
+ * ensures that there will be frees which return elements to the
+ * pool waking up the waiters.
+ */