1#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 
 
 
 
 
 
 
 2static inline void rwsem_set_owner(struct rw_semaphore *sem)
 3{
 4	sem->owner = current;
 5}
 6
 7static inline void rwsem_clear_owner(struct rw_semaphore *sem)
 8{
 9	sem->owner = NULL;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
10}
11
 
 
 
 
12#else
13static inline void rwsem_set_owner(struct rw_semaphore *sem)
14{
15}
16
17static inline void rwsem_clear_owner(struct rw_semaphore *sem)
 
 
 
 
18{
19}
20#endif

 1/*
 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.
 6 *
 7 * In essence, the owner field now has the following 3 states:
 8 *  1) 0
 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
15 */
16#define RWSEM_READER_OWNED	((struct task_struct *)1UL)
17
18#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
19/*
20 * All writes to owner are protected by WRITE_ONCE() to make sure that
21 * store tearing can't happen as optimistic spinners may read and use
22 * the owner value concurrently without lock. Read from owner, however,
23 * may not need READ_ONCE() as long as the pointer value is only used
24 * for comparison and isn't being dereferenced.
25 */
26static inline void rwsem_set_owner(struct rw_semaphore *sem)
27{
28	WRITE_ONCE(sem->owner, current);
29}
30
31static inline void rwsem_clear_owner(struct rw_semaphore *sem)
32{
33	WRITE_ONCE(sem->owner, NULL);
34}
35
36static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
37{
38	/*
39	 * We check the owner value first to make sure that we will only
40	 * do a write to the rwsem cacheline when it is really necessary
41	 * to minimize cacheline contention.
42	 */
43	if (sem->owner != RWSEM_READER_OWNED)
44		WRITE_ONCE(sem->owner, RWSEM_READER_OWNED);
45}
46
47static inline bool rwsem_owner_is_writer(struct task_struct *owner)
48{
49	return owner && owner != RWSEM_READER_OWNED;
50}
51
52static inline bool rwsem_owner_is_reader(struct task_struct *owner)
53{
54	return owner == RWSEM_READER_OWNED;
55}
56#else
57static inline void rwsem_set_owner(struct rw_semaphore *sem)
58{
59}
60
61static inline void rwsem_clear_owner(struct rw_semaphore *sem)
62{
63}
64
65static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
66{
67}
68#endif