From: Michal Hocko <mhocko@kernel.org> To: LKML <linux-kernel@vger.kernel.org> Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>, Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>, "David S. Miller" <davem@davemloft.net>, Tony Luck <tony.luck@intel.com>, Andrew Morton <akpm@linux-foundation.org>, Chris Zankel <chris@zankel.net>, Max Filippov <jcmvbkbc@gmail.com>, 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 <mhocko@suse.com> Subject: [RFC 02/12] locking, rwsem: drop explicit memory barriers Date: Tue, 02 Feb 2016 20:19:19 +0000 [thread overview] Message-ID: <1454444369-2146-3-git-send-email-mhocko@kernel.org> (raw) In-Reply-To: <1454444369-2146-1-git-send-email-mhocko@kernel.org> From: Michal Hocko <mhocko@suse.com> 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> --- 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
WARNING: multiple messages have this Message-ID (diff)
From: Michal Hocko <mhocko@kernel.org> To: LKML <linux-kernel@vger.kernel.org> Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>, Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>, "David S. Miller" <davem@davemloft.net>, Tony Luck <tony.luck@intel.com>, Andrew Morton <akpm@linux-foundation.org>, Chris Zankel <chris@zankel.net>, Max Filippov <jcmvbkbc@gmail.com>, 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 <mhocko@suse.com> Subject: [RFC 02/12] locking, rwsem: drop explicit memory barriers Date: Tue, 2 Feb 2016 21:19:19 +0100 [thread overview] Message-ID: <1454444369-2146-3-git-send-email-mhocko@kernel.org> (raw) In-Reply-To: <1454444369-2146-1-git-send-email-mhocko@kernel.org> From: Michal Hocko <mhocko@suse.com> 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> --- 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
next prev parent reply other threads:[~2016-02-02 20:19 UTC|newest] Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-02-02 20:19 [RFC 0/12] introduce down_write_killable for rw_semaphore Michal Hocko 2016-02-02 20:19 ` Michal Hocko 2016-02-02 20:19 ` [RFC 01/12] locking, rwsem: get rid of __down_write_nested Michal Hocko 2016-02-02 20:19 ` Michal Hocko 2016-02-02 20:19 ` Michal Hocko [this message] 2016-02-02 20:19 ` [RFC 02/12] locking, rwsem: drop explicit memory barriers Michal Hocko 2016-02-02 20:19 ` [RFC 03/12] locking, rwsem: introduce basis for down_write_killable Michal Hocko 2016-02-02 20:19 ` Michal Hocko 2016-02-02 20:19 ` [RFC 04/12] alpha, rwsem: provide __down_write_killable Michal Hocko 2016-02-02 20:19 ` Michal Hocko 2016-02-02 20:19 ` [RFC 05/12] ia64, " Michal Hocko 2016-02-02 20:19 ` Michal Hocko 2016-02-02 20:19 ` [RFC 06/12] s390, " Michal Hocko 2016-02-02 20:19 ` Michal Hocko 2016-02-02 20:19 ` [RFC 07/12] sh, " Michal Hocko 2016-02-02 20:19 ` Michal Hocko 2016-02-03 11:19 ` Sergei Shtylyov 2016-02-03 11:19 ` Sergei Shtylyov 2016-02-03 12:11 ` Michal Hocko 2016-02-03 12:11 ` Michal Hocko 2016-02-02 20:19 ` [RFC 08/12] sparc, " Michal Hocko 2016-02-02 20:19 ` Michal Hocko 2016-02-02 20:19 ` [RFC 09/12] xtensa, " Michal Hocko 2016-02-02 20:19 ` Michal Hocko 2016-02-02 20:19 ` [RFC 10/12] x86, rwsem: simplify __down_write Michal Hocko 2016-02-02 20:19 ` Michal Hocko 2016-02-03 8:10 ` Ingo Molnar 2016-02-03 8:10 ` Ingo Molnar 2016-02-03 12:10 ` Michal Hocko 2016-02-03 12:10 ` Michal Hocko 2016-06-03 16:13 ` Peter Zijlstra 2016-06-03 16:13 ` Peter Zijlstra 2016-06-03 22:34 ` Peter Zijlstra 2016-06-03 22:34 ` Peter Zijlstra 2016-06-09 14:40 ` David Howells 2016-06-09 14:40 ` David Howells 2016-06-09 17:36 ` Peter Zijlstra 2016-06-09 17:36 ` Peter Zijlstra 2016-06-10 16:39 ` Paul E. McKenney 2016-06-10 16:39 ` Paul E. McKenney 2016-02-02 20:19 ` [RFC 11/12] x86, rwsem: provide __down_write_killable Michal Hocko 2016-02-02 20:19 ` Michal Hocko 2016-02-17 16:41 ` [RFC 11/12 v1] " Michal Hocko 2016-02-17 16:41 ` Michal Hocko 2016-02-17 16:41 ` Michal Hocko 2016-02-17 16:41 ` Michal Hocko 2016-02-02 20:19 ` [RFC 12/12] locking, rwsem: provide down_write_killable Michal Hocko 2016-02-02 20:19 ` Michal Hocko 2016-02-19 12:15 ` [RFC 0/12] introduce down_write_killable for rw_semaphore Michal Hocko 2016-02-19 12:15 ` Michal Hocko 2016-03-09 12:18 ` Ingo Molnar 2016-03-09 12:18 ` Ingo Molnar 2016-03-09 12:56 ` Michal Hocko 2016-03-09 12:56 ` Michal Hocko 2016-03-09 13:17 ` Ingo Molnar 2016-03-09 13:17 ` Ingo Molnar 2016-03-09 13:28 ` Michal Hocko 2016-03-09 13:28 ` Michal Hocko 2016-03-09 13:43 ` Ingo Molnar 2016-03-09 13:43 ` Ingo Molnar 2016-03-09 14:41 ` Michal Hocko 2016-03-09 14:41 ` Michal Hocko 2016-03-10 10:24 ` Ingo Molnar 2016-03-10 10:24 ` Ingo Molnar
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