From 2e927c6422fea5ce36b24b00c2c84f2e9ead31b6 Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Thu, 7 Apr 2016 17:12:22 +0200 Subject: locking/rwsem: Drop explicit memory barriers 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 Cc: Andrew Morton Cc: Chris Zankel Cc: David S. Miller Cc: Linus Torvalds Cc: Max Filippov Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Signed-off-by: Davidlohr Bueso Cc: Signed-off-by: Jason Low Cc: Thomas Gleixner Cc: Tony Luck 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 --- arch/xtensa/include/asm/rwsem.h | 14 ++------------ 1 file changed, 2 insertions(+), 12 deletions(-) (limited to 'arch/xtensa') diff --git a/arch/xtensa/include/asm/rwsem.h b/arch/xtensa/include/asm/rwsem.h index 249619e7e7f2..593483f6e1ff 100644 --- a/arch/xtensa/include/asm/rwsem.h +++ b/arch/xtensa/include/asm/rwsem.h @@ -29,9 +29,7 @@ */ static inline void __down_read(struct rw_semaphore *sem) { - if (atomic_add_return(1,(atomic_t *)(&sem->count)) > 0) - smp_wmb(); - else + if (atomic_add_return(1,(atomic_t *)(&sem->count)) <= 0) rwsem_down_read_failed(sem); } @@ -42,7 +40,6 @@ static inline int __down_read_trylock(struct rw_semaphore *sem) while ((tmp = sem->count) >= 0) { if (tmp == cmpxchg(&sem->count, tmp, tmp + RWSEM_ACTIVE_READ_BIAS)) { - smp_wmb(); return 1; } } @@ -58,9 +55,7 @@ static inline void __down_write(struct rw_semaphore *sem) tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS, (atomic_t *)(&sem->count)); - if (tmp == RWSEM_ACTIVE_WRITE_BIAS) - smp_wmb(); - else + if (tmp != RWSEM_ACTIVE_WRITE_BIAS) rwsem_down_write_failed(sem); } @@ -70,7 +65,6 @@ static inline int __down_write_trylock(struct rw_semaphore *sem) tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE, RWSEM_ACTIVE_WRITE_BIAS); - smp_wmb(); return tmp == RWSEM_UNLOCKED_VALUE; } @@ -81,7 +75,6 @@ static inline void __up_read(struct rw_semaphore *sem) { int tmp; - smp_wmb(); tmp = atomic_sub_return(1,(atomic_t *)(&sem->count)); if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0) rwsem_wake(sem); @@ -92,7 +85,6 @@ static inline void __up_read(struct rw_semaphore *sem) */ static inline void __up_write(struct rw_semaphore *sem) { - smp_wmb(); if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS, (atomic_t *)(&sem->count)) < 0) rwsem_wake(sem); @@ -113,7 +105,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem) { int tmp; - smp_wmb(); tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count)); if (tmp < 0) rwsem_downgrade_wake(sem); @@ -124,7 +115,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem) */ static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem) { - smp_mb(); return atomic_add_return(delta, (atomic_t *)(&sem->count)); } -- cgit v1.2.3