+ /*
+ * Managership is governed by two mutexes - manager_arb and
+ * manager_mutex. manager_arb handles arbitration of manager role.
+ * Anyone who successfully grabs manager_arb wins the arbitration
+ * and becomes the manager. mutex_trylock() on pool->manager_arb
+ * failure while holding pool->lock reliably indicates that someone
+ * else is managing the pool and the worker which failed trylock
+ * can proceed to executing work items. This means that anyone
+ * grabbing manager_arb is responsible for actually performing
+ * manager duties. If manager_arb is grabbed and released without
+ * actual management, the pool may stall indefinitely.
+ *
+ * manager_mutex is used for exclusion of actual management
+ * operations. The holder of manager_mutex can be sure that none
+ * of management operations, including creation and destruction of
+ * workers, won't take place until the mutex is released. Because
+ * manager_mutex doesn't interfere with manager role arbitration,
+ * it is guaranteed that the pool's management, while may be
+ * delayed, won't be disturbed by someone else grabbing
+ * manager_mutex.
+ */