- * Lock is in the transition from CLS_HELD to CLS_CACHED. Lock is in
- * this state only while cl_unuse() is executing against it.
+ * This state is used to mark the lock is being used, or unused.
+ * We need this state because the lock may have several sublocks,
+ * so it's impossible to have an atomic way to bring all sublocks
+ * into CLS_HELD state at use case, or all sublocks to CLS_CACHED
+ * at unuse case.
+ * If a thread is referring to a lock, and it sees the lock is in this
+ * state, it must wait for the lock.
+ * See state diagram for details.