2 * The owner field of the rw_semaphore structure will be set to
3 * RWSEM_READ_OWNED when a reader grabs the lock. A writer will clear
4 * the owner field when it unlocks. A reader, on the other hand, will
5 * not touch the owner field when it unlocks.
7 * In essence, the owner field now has the following 3 states:
9 * - lock is free or the owner hasn't set the field yet
10 * 2) RWSEM_READER_OWNED
11 * - lock is currently or previously owned by readers (lock is free
12 * or not set by owner yet)
13 * 3) Other non-zero value
14 * - a writer owns the lock
16 #define RWSEM_READER_OWNED ((struct task_struct *)1UL)
18 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
19 static inline void rwsem_set_owner(struct rw_semaphore *sem)
24 static inline void rwsem_clear_owner(struct rw_semaphore *sem)
29 static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
32 * We check the owner value first to make sure that we will only
33 * do a write to the rwsem cacheline when it is really necessary
34 * to minimize cacheline contention.
36 if (sem->owner != RWSEM_READER_OWNED)
37 sem->owner = RWSEM_READER_OWNED;
40 static inline bool rwsem_owner_is_writer(struct task_struct *owner)
42 return owner && owner != RWSEM_READER_OWNED;
45 static inline bool rwsem_owner_is_reader(struct task_struct *owner)
47 return owner == RWSEM_READER_OWNED;
50 static inline void rwsem_set_owner(struct rw_semaphore *sem)
54 static inline void rwsem_clear_owner(struct rw_semaphore *sem)
58 static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)