1#ifndef _ASM_GENERIC_RWSEM_H
  2#define _ASM_GENERIC_RWSEM_H
  3
  4#ifndef _LINUX_RWSEM_H
  5#error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
  6#endif
  7
  8#ifdef __KERNEL__
  9
 10/*
 11 * R/W semaphores originally for PPC using the stuff in lib/rwsem.c.
 12 * Adapted largely from include/asm-i386/rwsem.h
 13 * by Paul Mackerras <paulus@samba.org>.
 14 */
 15
 16/*
 17 * the semaphore definition
 18 */
 19#ifdef CONFIG_64BIT
 20# define RWSEM_ACTIVE_MASK		0xffffffffL
 21#else
 22# define RWSEM_ACTIVE_MASK		0x0000ffffL
 23#endif
 24
 25#define RWSEM_UNLOCKED_VALUE		0x00000000L
 26#define RWSEM_ACTIVE_BIAS		0x00000001L
 27#define RWSEM_WAITING_BIAS		(-RWSEM_ACTIVE_MASK-1)
 28#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
 29#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
 30
 31/*
 32 * lock for reading
 33 */
 34static inline void __down_read(struct rw_semaphore *sem)
 35{
 36	if (unlikely(atomic_long_inc_return_acquire((atomic_long_t *)&sem->count) <= 0))
 37		rwsem_down_read_failed(sem);
 38}
 39
 40static inline int __down_read_trylock(struct rw_semaphore *sem)
 41{
 42	long tmp;
 43
 44	while ((tmp = atomic_long_read(&sem->count)) >= 0) {
 45		if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp,
 46				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
 47			return 1;
 48		}
 49	}
 50	return 0;
 51}
 52
 53/*
 54 * lock for writing
 55 */
 56static inline void __down_write(struct rw_semaphore *sem)
 57{
 58	long tmp;
 59
 60	tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
 61				     (atomic_long_t *)&sem->count);
 62	if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
 63		rwsem_down_write_failed(sem);
 64}
 65
 66static inline int __down_write_killable(struct rw_semaphore *sem)
 67{
 68	long tmp;
 69
 70	tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
 71				     (atomic_long_t *)&sem->count);
 72	if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
 73		if (IS_ERR(rwsem_down_write_failed_killable(sem)))
 74			return -EINTR;
 75	return 0;
 76}
 77
 78static inline int __down_write_trylock(struct rw_semaphore *sem)
 79{
 80	long tmp;
 81
 82	tmp = atomic_long_cmpxchg_acquire(&sem->count, RWSEM_UNLOCKED_VALUE,
 83		      RWSEM_ACTIVE_WRITE_BIAS);
 84	return tmp == RWSEM_UNLOCKED_VALUE;
 85}
 86
 87/*
 88 * unlock after reading
 89 */
 90static inline void __up_read(struct rw_semaphore *sem)
 91{
 92	long tmp;
 93
 94	tmp = atomic_long_dec_return_release((atomic_long_t *)&sem->count);
 95	if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))
 96		rwsem_wake(sem);
 97}
 98
 99/*
100 * unlock after writing
101 */
102static inline void __up_write(struct rw_semaphore *sem)
103{
104	if (unlikely(atomic_long_sub_return_release(RWSEM_ACTIVE_WRITE_BIAS,
105				 (atomic_long_t *)&sem->count) < 0))
106		rwsem_wake(sem);
107}
108
109/*
110 * downgrade write lock to read lock
111 */
112static inline void __downgrade_write(struct rw_semaphore *sem)
113{
114	long tmp;
115
116	/*
117	 * When downgrading from exclusive to shared ownership,
118	 * anything inside the write-locked region cannot leak
119	 * into the read side. In contrast, anything in the
120	 * read-locked region is ok to be re-ordered into the
121	 * write side. As such, rely on RELEASE semantics.
122	 */
123	tmp = atomic_long_add_return_release(-RWSEM_WAITING_BIAS,
124				     (atomic_long_t *)&sem->count);
125	if (tmp < 0)
126		rwsem_downgrade_wake(sem);
127}
128
129#endif	/* __KERNEL__ */
130#endif	/* _ASM_GENERIC_RWSEM_H */