125 lines
2.7 KiB
C
125 lines
2.7 KiB
C
/*
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* rwsem.h: R/W semaphores implemented using CAS
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*
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* Written by David S. Miller (davem@redhat.com), 2001.
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* Derived from asm-i386/rwsem.h
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*/
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#ifndef _SPARC64_RWSEM_H
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#define _SPARC64_RWSEM_H
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#ifndef _LINUX_RWSEM_H
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#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
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#endif
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#ifdef __KERNEL__
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#define RWSEM_UNLOCKED_VALUE 0x00000000L
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#define RWSEM_ACTIVE_BIAS 0x00000001L
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#define RWSEM_ACTIVE_MASK 0xffffffffL
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#define RWSEM_WAITING_BIAS (-RWSEM_ACTIVE_MASK-1)
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#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
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#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
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/*
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* lock for reading
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*/
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static inline void __down_read(struct rw_semaphore *sem)
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{
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if (unlikely(atomic64_inc_return((atomic64_t *)(&sem->count)) <= 0L))
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rwsem_down_read_failed(sem);
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}
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static inline int __down_read_trylock(struct rw_semaphore *sem)
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{
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long tmp;
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while ((tmp = sem->count) >= 0L) {
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if (tmp == cmpxchg(&sem->count, tmp,
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tmp + RWSEM_ACTIVE_READ_BIAS)) {
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return 1;
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}
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}
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return 0;
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}
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/*
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* lock for writing
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*/
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static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
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{
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long tmp;
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tmp = atomic64_add_return(RWSEM_ACTIVE_WRITE_BIAS,
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(atomic64_t *)(&sem->count));
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if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
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rwsem_down_write_failed(sem);
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}
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static inline void __down_write(struct rw_semaphore *sem)
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{
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__down_write_nested(sem, 0);
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}
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static inline int __down_write_trylock(struct rw_semaphore *sem)
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{
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long tmp;
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tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
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RWSEM_ACTIVE_WRITE_BIAS);
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return tmp == RWSEM_UNLOCKED_VALUE;
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}
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/*
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* unlock after reading
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*/
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static inline void __up_read(struct rw_semaphore *sem)
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{
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long tmp;
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tmp = atomic64_dec_return((atomic64_t *)(&sem->count));
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if (unlikely(tmp < -1L && (tmp & RWSEM_ACTIVE_MASK) == 0L))
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rwsem_wake(sem);
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}
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/*
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* unlock after writing
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*/
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static inline void __up_write(struct rw_semaphore *sem)
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{
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if (unlikely(atomic64_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
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(atomic64_t *)(&sem->count)) < 0L))
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rwsem_wake(sem);
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}
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/*
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* implement atomic add functionality
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*/
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static inline void rwsem_atomic_add(long delta, struct rw_semaphore *sem)
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{
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atomic64_add(delta, (atomic64_t *)(&sem->count));
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}
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/*
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* downgrade write lock to read lock
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*/
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static inline void __downgrade_write(struct rw_semaphore *sem)
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{
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long tmp;
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tmp = atomic64_add_return(-RWSEM_WAITING_BIAS, (atomic64_t *)(&sem->count));
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if (tmp < 0L)
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rwsem_downgrade_wake(sem);
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}
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/*
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* implement exchange and add functionality
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*/
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static inline long rwsem_atomic_update(long delta, struct rw_semaphore *sem)
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{
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return atomic64_add_return(delta, (atomic64_t *)(&sem->count));
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}
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#endif /* __KERNEL__ */
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#endif /* _SPARC64_RWSEM_H */
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