+ * rcu_stress_count: Histogram of "ages" of structures seen by readers. If any
+ * entries past the first two are non-zero, RCU is broken. The age of a newly
+ * allocated structure is zero, it becomes one when removed from reader
+ * visibility, and is incremented once per grace period subsequently -- and is
+ * freed after passing through (RCU_STRESS_PIPE_LEN-2) grace periods. Since
+ * this tests only has one true writer (there are fake writers), only buckets at
+ * indexes 0 and 1 should be none-zero.
+ *