130 строки
3.0 KiB
C
130 строки
3.0 KiB
C
#ifndef _ASM_GENERIC_RWSEM_H
|
|
#define _ASM_GENERIC_RWSEM_H
|
|
|
|
#ifndef _LINUX_RWSEM_H
|
|
#error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
|
|
#endif
|
|
|
|
#ifdef __KERNEL__
|
|
|
|
/*
|
|
* R/W semaphores originally for PPC using the stuff in lib/rwsem.c.
|
|
* Adapted largely from include/asm-i386/rwsem.h
|
|
* by Paul Mackerras <paulus@samba.org>.
|
|
*/
|
|
|
|
/*
|
|
* the semaphore definition
|
|
*/
|
|
#ifdef CONFIG_64BIT
|
|
# define RWSEM_ACTIVE_MASK 0xffffffffL
|
|
#else
|
|
# define RWSEM_ACTIVE_MASK 0x0000ffffL
|
|
#endif
|
|
|
|
#define RWSEM_UNLOCKED_VALUE 0x00000000L
|
|
#define RWSEM_ACTIVE_BIAS 0x00000001L
|
|
#define RWSEM_WAITING_BIAS (-RWSEM_ACTIVE_MASK-1)
|
|
#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
|
|
#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
|
|
|
|
/*
|
|
* lock for reading
|
|
*/
|
|
static inline void __down_read(struct rw_semaphore *sem)
|
|
{
|
|
if (unlikely(atomic_long_inc_return_acquire(&sem->count) <= 0))
|
|
rwsem_down_read_failed(sem);
|
|
}
|
|
|
|
static inline int __down_read_trylock(struct rw_semaphore *sem)
|
|
{
|
|
long tmp;
|
|
|
|
while ((tmp = atomic_long_read(&sem->count)) >= 0) {
|
|
if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp,
|
|
tmp + RWSEM_ACTIVE_READ_BIAS)) {
|
|
return 1;
|
|
}
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* lock for writing
|
|
*/
|
|
static inline void __down_write(struct rw_semaphore *sem)
|
|
{
|
|
long tmp;
|
|
|
|
tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
|
|
&sem->count);
|
|
if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
|
|
rwsem_down_write_failed(sem);
|
|
}
|
|
|
|
static inline int __down_write_killable(struct rw_semaphore *sem)
|
|
{
|
|
long tmp;
|
|
|
|
tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,
|
|
&sem->count);
|
|
if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
|
|
if (IS_ERR(rwsem_down_write_failed_killable(sem)))
|
|
return -EINTR;
|
|
return 0;
|
|
}
|
|
|
|
static inline int __down_write_trylock(struct rw_semaphore *sem)
|
|
{
|
|
long tmp;
|
|
|
|
tmp = atomic_long_cmpxchg_acquire(&sem->count, RWSEM_UNLOCKED_VALUE,
|
|
RWSEM_ACTIVE_WRITE_BIAS);
|
|
return tmp == RWSEM_UNLOCKED_VALUE;
|
|
}
|
|
|
|
/*
|
|
* unlock after reading
|
|
*/
|
|
static inline void __up_read(struct rw_semaphore *sem)
|
|
{
|
|
long tmp;
|
|
|
|
tmp = atomic_long_dec_return_release(&sem->count);
|
|
if (unlikely(tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0))
|
|
rwsem_wake(sem);
|
|
}
|
|
|
|
/*
|
|
* unlock after writing
|
|
*/
|
|
static inline void __up_write(struct rw_semaphore *sem)
|
|
{
|
|
if (unlikely(atomic_long_sub_return_release(RWSEM_ACTIVE_WRITE_BIAS,
|
|
&sem->count) < 0))
|
|
rwsem_wake(sem);
|
|
}
|
|
|
|
/*
|
|
* downgrade write lock to read lock
|
|
*/
|
|
static inline void __downgrade_write(struct rw_semaphore *sem)
|
|
{
|
|
long tmp;
|
|
|
|
/*
|
|
* When downgrading from exclusive to shared ownership,
|
|
* anything inside the write-locked region cannot leak
|
|
* into the read side. In contrast, anything in the
|
|
* read-locked region is ok to be re-ordered into the
|
|
* write side. As such, rely on RELEASE semantics.
|
|
*/
|
|
tmp = atomic_long_add_return_release(-RWSEM_WAITING_BIAS, &sem->count);
|
|
if (tmp < 0)
|
|
rwsem_downgrade_wake(sem);
|
|
}
|
|
|
|
#endif /* __KERNEL__ */
|
|
#endif /* _ASM_GENERIC_RWSEM_H */
|