1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _ASM_GENERIC_RWSEM_H
3 #define _ASM_GENERIC_RWSEM_H
6 #error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
12 * R/W semaphores originally for PPC using the stuff in lib/rwsem.c.
13 * Adapted largely from include/asm-i386/rwsem.h
14 * by Paul Mackerras <paulus@samba.org>.
18 * the semaphore definition
21 # define RWSEM_ACTIVE_MASK 0xffffffffL
23 # define RWSEM_ACTIVE_MASK 0x0000ffffL
26 #define RWSEM_UNLOCKED_VALUE 0x00000000L
27 #define RWSEM_ACTIVE_BIAS 0x00000001L
28 #define RWSEM_WAITING_BIAS (-RWSEM_ACTIVE_MASK-1)
29 #define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
30 #define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
35 static inline void __down_read(struct rw_semaphore *sem)
37 if (unlikely(atomic_long_inc_return_acquire(&sem->count) <= 0))
38 rwsem_down_read_failed(sem);
41 static inline int __down_read_trylock(struct rw_semaphore *sem)
45 while ((tmp = atomic_long_read(&sem->count)) >= 0) {
46 if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp,
47 tmp + RWSEM_ACTIVE_READ_BIAS)) {
57 static inline void __down_write(struct rw_semaphore *sem)
61 tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
63 if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
64 rwsem_down_write_failed(sem);
67 static inline int __down_write_killable(struct rw_semaphore *sem)
71 tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
73 if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
74 if (IS_ERR(rwsem_down_write_failed_killable(sem)))
79 static inline int __down_write_trylock(struct rw_semaphore *sem)
83 tmp = atomic_long_cmpxchg_acquire(&sem->count, RWSEM_UNLOCKED_VALUE,
84 RWSEM_ACTIVE_WRITE_BIAS);
85 return tmp == RWSEM_UNLOCKED_VALUE;
89 * unlock after reading
91 static inline void __up_read(struct rw_semaphore *sem)
95 tmp = atomic_long_dec_return_release(&sem->count);
96 if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))
101 * unlock after writing
103 static inline void __up_write(struct rw_semaphore *sem)
105 if (unlikely(atomic_long_sub_return_release(RWSEM_ACTIVE_WRITE_BIAS,
111 * downgrade write lock to read lock
113 static inline void __downgrade_write(struct rw_semaphore *sem)
118 * When downgrading from exclusive to shared ownership,
119 * anything inside the write-locked region cannot leak
120 * into the read side. In contrast, anything in the
121 * read-locked region is ok to be re-ordered into the
122 * write side. As such, rely on RELEASE semantics.
124 tmp = atomic_long_add_return_release(-RWSEM_WAITING_BIAS, &sem->count);
126 rwsem_downgrade_wake(sem);
129 #endif /* __KERNEL__ */
130 #endif /* _ASM_GENERIC_RWSEM_H */