39  *  - Bit 1: RWSEM_NONSPINNABLE - Cannot spin on a reader-owned lock
41  * When the rwsem is reader-owned and a spinning writer has timed out,
47  * When a reader acquires a rwsem, it will also puts its task_struct
50  * for a free or reader-owned rwsem, the owner value may contain
51  * information about the last reader that acquires the rwsem.
54  * seems to hang on a reader owned rwsem especially if only one reader
58  * A fast path reader optimistic lock stealing is supported when the rwsem
88  * Bits 8-62 - 55-bit reader count
97  * Bits 8-30 - 23-bit reader count
102  * just in case we need to use up more of the reader bits for other purpose
105  * atomic_long_fetch_add() is used to obtain reader lock, whereas
161  * The task_struct pointer of the last owning reader will be left in
168  * The reader non-spinnable bit is preserved.
185  * Return true if the rwsem is owned by a reader.
204  * is a task pointer in owner of a reader-owned rwsem, it will be the
301  * (2) some of the reader bits are set in count, and
304  * Having some reader bits set is not enough to guarantee a readers owned
447 	 * No reader wakeup if there are too many of them already.  in rwsem_mark_wake()
453 	 * Writers might steal the lock before we grant it to the next reader.  in rwsem_mark_wake()
454 	 * We prefer to do the first reader grant before counting readers  in rwsem_mark_wake()
480 		 * Set it to reader-owned to give spinners an early  in rwsem_mark_wake()
482 		 * The reader nonspinnable bit seen at slowpath entry of  in rwsem_mark_wake()
483 		 * the reader is copied over.  in rwsem_mark_wake()
496 	 * reader phase (first waiter is a reader), all readers are eligible  in rwsem_mark_wake()
502 	 * the reader count may be decremented before it is incremented. It  in rwsem_mark_wake()
505 	 * do an unlock before the reader count increment.  in rwsem_mark_wake()
508 	 *    fully increment the reader count in rwsem.  in rwsem_mark_wake()
541 		 * When we've woken a reader, we no longer need to force  in rwsem_mark_wake()
559 		 * Ensure calling get_task_struct() before setting the reader  in rwsem_mark_wake()
567 		 * after setting the reader waiter to nil.  in rwsem_mark_wake()
575  * This function is called from the out_nolock path of both the reader and
677  *   OWNER_READER: when owner changes and the new owner may be a reader.
801  * Calculate reader-owned rwsem spinning threshold for writer
860 		 * Time-based reader-owned rwsem optimistic spinning  in rwsem_optimistic_spin()
865 			 * the owner state changes from non-reader to reader.  in rwsem_optimistic_spin()
867 			 * 2 reader phases and have the threshold reset at  in rwsem_optimistic_spin()
868 			 * the beginning of the 2nd reader phase.  in rwsem_optimistic_spin()
948  * only be called when the reader count reaches 0.
979  * reader-owned, wake up read lock waiters in queue front or wake up any
982  * This is being called from both reader and writer slow paths.
1022 	 * Reader optimistic lock stealing.  in rwsem_down_read_slowpath()
1030 		 * the first reader.  in rwsem_down_read_slowpath()
1053 		 * by a writer, this reader can exit the slowpath and return  in rwsem_down_read_slowpath()