From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: [PATCH 02/11] locking, rwsem: drop explicit memory barriers Date: Mon, 29 Feb 2016 13:58:16 +0100 Message-ID: <1456750705-7141-3-git-send-email-mhocko@kernel.org> References: <1456750705-7141-1-git-send-email-mhocko@kernel.org> Return-path: In-Reply-To: <1456750705-7141-1-git-send-email-mhocko@kernel.org> Sender: linux-ia64-owner@vger.kernel.org To: LKML Cc: Peter Zijlstra , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , "David S. Miller" , Tony Luck , Andrew Morton , Chris Zankel , Max Filippov , x86@kernel.org, linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-arch@vger.kernel.org, Michal Hocko List-Id: linux-arch.vger.kernel.org From: Michal Hocko 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 --- arch/sh/include/asm/rwsem.h | 14 ++------------ arch/xtensa/include/asm/rwsem.h | 14 ++------------ 2 files changed, 4 insertions(+), 24 deletions(-) diff --git a/arch/sh/include/asm/rwsem.h b/arch/sh/include/asm/rwsem.h index a5104bebd1eb..f6c951c7a875 100644 --- a/arch/sh/include/asm/rwsem.h +++ b/arch/sh/include/asm/rwsem.h @@ -24,9 +24,7 @@ */ static inline void __down_read(struct rw_semaphore *sem) { - if (atomic_inc_return((atomic_t *)(&sem->count)) > 0) - smp_wmb(); - else + if (atomic_inc_return((atomic_t *)(&sem->count)) <= 0) rwsem_down_read_failed(sem); } @@ -37,7 +35,6 @@ 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; } } @@ -53,9 +50,7 @@ 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); } @@ -65,7 +60,6 @@ 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; } @@ -76,7 +70,6 @@ static inline void __up_read(struct rw_semaphore *sem) { int tmp; - smp_wmb(); tmp = atomic_dec_return((atomic_t *)(&sem->count)); if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0) rwsem_wake(sem); @@ -87,7 +80,6 @@ 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); @@ -108,7 +100,6 @@ 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); @@ -119,7 +110,6 @@ 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)); } 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)); } -- 2.7.0 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f65.google.com ([74.125.82.65]:33251 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752623AbcB2M6i (ORCPT ); Mon, 29 Feb 2016 07:58:38 -0500 From: Michal Hocko Subject: [PATCH 02/11] locking, rwsem: drop explicit memory barriers Date: Mon, 29 Feb 2016 13:58:16 +0100 Message-ID: <1456750705-7141-3-git-send-email-mhocko@kernel.org> In-Reply-To: <1456750705-7141-1-git-send-email-mhocko@kernel.org> References: <1456750705-7141-1-git-send-email-mhocko@kernel.org> Sender: linux-arch-owner@vger.kernel.org List-ID: To: LKML Cc: Peter Zijlstra , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , "David S. Miller" , Tony Luck , Andrew Morton , Chris Zankel , Max Filippov , x86@kernel.org, linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-arch@vger.kernel.org, Michal Hocko Message-ID: <20160229125816.J6vnlFCCa5CEjGld8t8IUfLvBfLSeu22bOj26z71Cn4@z> From: Michal Hocko 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 --- arch/sh/include/asm/rwsem.h | 14 ++------------ arch/xtensa/include/asm/rwsem.h | 14 ++------------ 2 files changed, 4 insertions(+), 24 deletions(-) diff --git a/arch/sh/include/asm/rwsem.h b/arch/sh/include/asm/rwsem.h index a5104bebd1eb..f6c951c7a875 100644 --- a/arch/sh/include/asm/rwsem.h +++ b/arch/sh/include/asm/rwsem.h @@ -24,9 +24,7 @@ */ static inline void __down_read(struct rw_semaphore *sem) { - if (atomic_inc_return((atomic_t *)(&sem->count)) > 0) - smp_wmb(); - else + if (atomic_inc_return((atomic_t *)(&sem->count)) <= 0) rwsem_down_read_failed(sem); } @@ -37,7 +35,6 @@ 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; } } @@ -53,9 +50,7 @@ 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); } @@ -65,7 +60,6 @@ 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; } @@ -76,7 +70,6 @@ static inline void __up_read(struct rw_semaphore *sem) { int tmp; - smp_wmb(); tmp = atomic_dec_return((atomic_t *)(&sem->count)); if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0) rwsem_wake(sem); @@ -87,7 +80,6 @@ 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); @@ -108,7 +100,6 @@ 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); @@ -119,7 +110,6 @@ 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)); } 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)); } -- 2.7.0