From patchwork Mon Feb 29 12:58:16 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Michal Hocko X-Patchwork-Id: 589935 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id F13251402BF for ; Tue, 1 Mar 2016 00:01:29 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753486AbcB2M6w (ORCPT ); Mon, 29 Feb 2016 07:58:52 -0500 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 Received: by mail-wm0-f65.google.com with SMTP id n186so9933761wmn.0; Mon, 29 Feb 2016 04:58:36 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=8sTM0xjn1d43o1pSE2y341LZtDwzxxoe4SL+sHmtwsQ=; b=a+0K+P895ifjuVBurkdVehsNk8bo56JQAude4sdQcndFvrSj+bigGqlM7fSsogAnoy 3Iqyt40iiUTErXhJJ8+5vrE4DtOoG5x0uy7kmT1rtOWJ28ytVmkKfh4EYybmXVaJGD2A X2CxQ0hoNZ3psCMKoevvhXtOLjMyLDZPyR44geCNdD9j4PavyaAvaDWyQZmhH+Opygkc BYjDK3DJCSoxh7HQM3U5qvNQsUCYRJ/kO+rn+RkTBnlk5JzF52UqSQ78qixAITVNeqZH 9QO3OCeDAKD2R9Yvaq/IGeS2eTTZOt8g9nSkOnTeh5hcEI9RPW3WCOY13x5tIeMBEmkc de2g== X-Gm-Message-State: AD7BkJK+x27Y19IkahEwAL0EwVfqY3uu1ONqhcFJgY6bYypXuL7tPLWSLuL7kuylTUApJQ== X-Received: by 10.194.2.41 with SMTP id 9mr16398023wjr.10.1456750715589; Mon, 29 Feb 2016 04:58:35 -0800 (PST) Received: from tiehlicka.suse.cz (bband-dyn69.95-103-50.t-com.sk. [95.103.50.69]) by smtp.gmail.com with ESMTPSA id lh1sm25728400wjb.20.2016.02.29.04.58.34 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 29 Feb 2016 04:58:35 -0800 (PST) From: Michal Hocko 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 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> X-Mailer: git-send-email 2.7.0 In-Reply-To: <1456750705-7141-1-git-send-email-mhocko@kernel.org> References: <1456750705-7141-1-git-send-email-mhocko@kernel.org> Sender: sparclinux-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: sparclinux@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)); }