From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753117AbbJFQWJ (ORCPT ); Tue, 6 Oct 2015 12:22:09 -0400 Received: from terminus.zytor.com ([198.137.202.10]:34970 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752440AbbJFQWH (ORCPT ); Tue, 6 Oct 2015 12:22:07 -0400 Date: Tue, 6 Oct 2015 09:18:47 -0700 From: tip-bot for Davidlohr Bueso Message-ID: Cc: akpm@linux-foundation.org, paulmck@linux.vnet.ibm.com, dave@stgolabs.net, tglx@linutronix.de, will.deacon@arm.com, peterz@infradead.org, hpa@zytor.com, torvalds@linux-foundation.org, dbueso@suse.de, linux-kernel@vger.kernel.org, mingo@kernel.org Reply-To: dave@stgolabs.net, will.deacon@arm.com, tglx@linutronix.de, paulmck@linux.vnet.ibm.com, akpm@linux-foundation.org, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, mingo@kernel.org, dbueso@suse.de, hpa@zytor.com, peterz@infradead.org In-Reply-To: <1443643395-17016-3-git-send-email-dave@stgolabs.net> References: <1443643395-17016-3-git-send-email-dave@stgolabs.net> To: linux-tip-commits@vger.kernel.org Subject: [tip:locking/core] locking/mutex: Use acquire/release semantics Git-Commit-ID: 81a43adae3b943193fb3afd20a36a7482332f964 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 81a43adae3b943193fb3afd20a36a7482332f964 Gitweb: http://git.kernel.org/tip/81a43adae3b943193fb3afd20a36a7482332f964 Author: Davidlohr Bueso AuthorDate: Wed, 30 Sep 2015 13:03:12 -0700 Committer: Ingo Molnar CommitDate: Tue, 6 Oct 2015 17:28:20 +0200 locking/mutex: Use acquire/release semantics As of 654672d4ba1 (locking/atomics: Add _{acquire|release|relaxed}() variants of some atomic operations) and 6d79ef2d30e (locking, asm-generic: Add _{relaxed|acquire|release}() variants for 'atomic_long_t'), weakly ordered archs can benefit from more relaxed use of barriers when locking and unlocking, instead of regular full barrier semantics. While currently only arm64 supports such optimizations, updating corresponding locking primitives serves for other archs to immediately benefit as well, once the necessary machinery is implemented of course. Signed-off-by: Davidlohr Bueso Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Thomas Gleixner Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Paul E.McKenney Cc: Peter Zijlstra Cc: Will Deacon Cc: linux-kernel@vger.kernel.org Link: http://lkml.kernel.org/r/1443643395-17016-3-git-send-email-dave@stgolabs.net Signed-off-by: Ingo Molnar --- include/asm-generic/mutex-dec.h | 8 ++++---- include/asm-generic/mutex-xchg.h | 10 +++++----- kernel/locking/mutex.c | 9 +++++---- 3 files changed, 14 insertions(+), 13 deletions(-) diff --git a/include/asm-generic/mutex-dec.h b/include/asm-generic/mutex-dec.h index d4f9fb4..fd694cf 100644 --- a/include/asm-generic/mutex-dec.h +++ b/include/asm-generic/mutex-dec.h @@ -20,7 +20,7 @@ static inline void __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *)) { - if (unlikely(atomic_dec_return(count) < 0)) + if (unlikely(atomic_dec_return_acquire(count) < 0)) fail_fn(count); } @@ -35,7 +35,7 @@ __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *)) static inline int __mutex_fastpath_lock_retval(atomic_t *count) { - if (unlikely(atomic_dec_return(count) < 0)) + if (unlikely(atomic_dec_return_acquire(count) < 0)) return -1; return 0; } @@ -56,7 +56,7 @@ __mutex_fastpath_lock_retval(atomic_t *count) static inline void __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *)) { - if (unlikely(atomic_inc_return(count) <= 0)) + if (unlikely(atomic_inc_return_release(count) <= 0)) fail_fn(count); } @@ -80,7 +80,7 @@ __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *)) static inline int __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *)) { - if (likely(atomic_cmpxchg(count, 1, 0) == 1)) + if (likely(atomic_cmpxchg_acquire(count, 1, 0) == 1)) return 1; return 0; } diff --git a/include/asm-generic/mutex-xchg.h b/include/asm-generic/mutex-xchg.h index f169ec0..a6b4a7b 100644 --- a/include/asm-generic/mutex-xchg.h +++ b/include/asm-generic/mutex-xchg.h @@ -31,7 +31,7 @@ __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *)) * to ensure that any waiting tasks are woken up by the * unlock slow path. */ - if (likely(atomic_xchg(count, -1) != 1)) + if (likely(atomic_xchg_acquire(count, -1) != 1)) fail_fn(count); } @@ -46,7 +46,7 @@ __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *)) static inline int __mutex_fastpath_lock_retval(atomic_t *count) { - if (unlikely(atomic_xchg(count, 0) != 1)) + if (unlikely(atomic_xchg_acquire(count, 0) != 1)) if (likely(atomic_xchg(count, -1) != 1)) return -1; return 0; @@ -67,7 +67,7 @@ __mutex_fastpath_lock_retval(atomic_t *count) static inline void __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *)) { - if (unlikely(atomic_xchg(count, 1) != 0)) + if (unlikely(atomic_xchg_release(count, 1) != 0)) fail_fn(count); } @@ -91,7 +91,7 @@ __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *)) static inline int __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *)) { - int prev = atomic_xchg(count, 0); + int prev = atomic_xchg_acquire(count, 0); if (unlikely(prev < 0)) { /* @@ -105,7 +105,7 @@ __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *)) * owner's unlock path needlessly, but that's not a problem * in practice. ] */ - prev = atomic_xchg(count, prev); + prev = atomic_xchg_acquire(count, prev); if (prev < 0) prev = 0; } diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 4cccea6..0551c21 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -277,7 +277,7 @@ static inline int mutex_can_spin_on_owner(struct mutex *lock) static inline bool mutex_try_to_acquire(struct mutex *lock) { return !mutex_is_locked(lock) && - (atomic_cmpxchg(&lock->count, 1, 0) == 1); + (atomic_cmpxchg_acquire(&lock->count, 1, 0) == 1); } /* @@ -529,7 +529,8 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, * Once more, try to acquire the lock. Only try-lock the mutex if * it is unlocked to reduce unnecessary xchg() operations. */ - if (!mutex_is_locked(lock) && (atomic_xchg(&lock->count, 0) == 1)) + if (!mutex_is_locked(lock) && + (atomic_xchg_acquire(&lock->count, 0) == 1)) goto skip_wait; debug_mutex_lock_common(lock, &waiter); @@ -553,7 +554,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, * non-negative in order to avoid unnecessary xchg operations: */ if (atomic_read(&lock->count) >= 0 && - (atomic_xchg(&lock->count, -1) == 1)) + (atomic_xchg_acquire(&lock->count, -1) == 1)) break; /* @@ -867,7 +868,7 @@ static inline int __mutex_trylock_slowpath(atomic_t *lock_count) spin_lock_mutex(&lock->wait_lock, flags); - prev = atomic_xchg(&lock->count, -1); + prev = atomic_xchg_acquire(&lock->count, -1); if (likely(prev == 1)) { mutex_set_owner(lock); mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);