2e927c6422
sh and xtensa seem to be the only architectures which use explicit
memory barriers for rw_semaphore operations even though they are not
really needed because there is the full memory barrier is always implied
by atomic_{inc,dec,add,sub}_return() resp. cmpxchg(). Remove them.
Signed-off-by: Michal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Zankel <chris@zankel.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Signed-off-by: Jason Low <jason.low2@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-alpha@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: linux-ia64@vger.kernel.org
Cc: linux-s390@vger.kernel.org
Cc: linux-sh@vger.kernel.org
Cc: linux-xtensa@linux-xtensa.org
Cc: sparclinux@vger.kernel.org
Link: http://lkml.kernel.org/r/1460041951-22347-3-git-send-email-mhocko@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
118 lines
2.4 KiB
C
118 lines
2.4 KiB
C
/*
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* include/asm-sh/rwsem.h: R/W semaphores for SH using the stuff
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* in lib/rwsem.c.
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*/
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#ifndef _ASM_SH_RWSEM_H
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#define _ASM_SH_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 0x00000000
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#define RWSEM_ACTIVE_BIAS 0x00000001
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#define RWSEM_ACTIVE_MASK 0x0000ffff
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#define RWSEM_WAITING_BIAS (-0x00010000)
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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 (atomic_inc_return((atomic_t *)(&sem->count)) <= 0)
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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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int tmp;
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while ((tmp = sem->count) >= 0) {
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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(struct rw_semaphore *sem)
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{
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int tmp;
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tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
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(atomic_t *)(&sem->count));
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if (tmp != RWSEM_ACTIVE_WRITE_BIAS)
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rwsem_down_write_failed(sem);
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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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int 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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int tmp;
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tmp = atomic_dec_return((atomic_t *)(&sem->count));
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if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
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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 (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
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(atomic_t *)(&sem->count)) < 0)
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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(int delta, struct rw_semaphore *sem)
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{
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atomic_add(delta, (atomic_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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int tmp;
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tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
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if (tmp < 0)
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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 int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
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{
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return atomic_add_return(delta, (atomic_t *)(&sem->count));
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}
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#endif /* __KERNEL__ */
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#endif /* _ASM_SH_RWSEM_H */
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