From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: [RFC PATCH-tip/locking/core v3 01/10] locking/osq: Make lock/unlock proper acquire/release barrier Date: Fri, 17 Jun 2016 11:41:27 -0400 Message-ID: <1466178096-5623-2-git-send-email-Waiman.Long@hpe.com> References: <1466178096-5623-1-git-send-email-Waiman.Long@hpe.com> Return-path: In-Reply-To: <1466178096-5623-1-git-send-email-Waiman.Long@hpe.com> Sender: linux-doc-owner@vger.kernel.org To: Peter Zijlstra , Ingo Molnar Cc: linux-kernel@vger.kernel.org, x86@kernel.org, linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, Davidlohr Bueso , Jason Low , Dave Chinner , Jonathan Corbet , Scott J Norton , Douglas Hatch , Waiman Long List-Id: linux-arch.vger.kernel.org The osq_lock() and osq_unlock() function may not provide the necessary acquire and release barrier in some cases. This patch makes sure that the proper barriers are provided when osq_lock() is successful or when osq_unlock() is called. The change on the unlock side is more for documentation purpose than is actually needed. Suggested-by: Peter Zijlstra (Intel) Signed-off-by: Waiman Long --- kernel/locking/osq_lock.c | 7 ++++++- 1 files changed, 6 insertions(+), 1 deletions(-) diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 05a3785..d957b90 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -124,6 +124,11 @@ bool osq_lock(struct optimistic_spin_queue *lock) cpu_relax_lowlatency(); } + /* + * Add an acquire memory barrier for pairing with the release barrier + * in unlock. + */ + smp_acquire__after_ctrl_dep(); return true; unqueue: @@ -198,7 +203,7 @@ void osq_unlock(struct optimistic_spin_queue *lock) * Second most likely case. */ node = this_cpu_ptr(&osq_node); - next = xchg(&node->next, NULL); + next = xchg_release(&node->next, NULL); if (next) { WRITE_ONCE(next->locked, 1); return; -- 1.7.1 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from g4t3428.houston.hpe.com ([15.241.140.76]:28648 "EHLO g4t3428.houston.hpe.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933745AbcFQPmN (ORCPT ); Fri, 17 Jun 2016 11:42:13 -0400 From: Waiman Long Subject: [RFC PATCH-tip/locking/core v3 01/10] locking/osq: Make lock/unlock proper acquire/release barrier Date: Fri, 17 Jun 2016 11:41:27 -0400 Message-ID: <1466178096-5623-2-git-send-email-Waiman.Long@hpe.com> In-Reply-To: <1466178096-5623-1-git-send-email-Waiman.Long@hpe.com> References: <1466178096-5623-1-git-send-email-Waiman.Long@hpe.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Peter Zijlstra , Ingo Molnar Cc: linux-kernel@vger.kernel.org, x86@kernel.org, linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, Davidlohr Bueso , Jason Low , Dave Chinner , Jonathan Corbet , Scott J Norton , Douglas Hatch , Waiman Long Message-ID: <20160617154127.NckXWFEUNDLbgtjfDQuEPJPjbixRTc7dO0mbv3IQUh0@z> The osq_lock() and osq_unlock() function may not provide the necessary acquire and release barrier in some cases. This patch makes sure that the proper barriers are provided when osq_lock() is successful or when osq_unlock() is called. The change on the unlock side is more for documentation purpose than is actually needed. Suggested-by: Peter Zijlstra (Intel) Signed-off-by: Waiman Long --- kernel/locking/osq_lock.c | 7 ++++++- 1 files changed, 6 insertions(+), 1 deletions(-) diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 05a3785..d957b90 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -124,6 +124,11 @@ bool osq_lock(struct optimistic_spin_queue *lock) cpu_relax_lowlatency(); } + /* + * Add an acquire memory barrier for pairing with the release barrier + * in unlock. + */ + smp_acquire__after_ctrl_dep(); return true; unqueue: @@ -198,7 +203,7 @@ void osq_unlock(struct optimistic_spin_queue *lock) * Second most likely case. */ node = this_cpu_ptr(&osq_node); - next = xchg(&node->next, NULL); + next = xchg_release(&node->next, NULL); if (next) { WRITE_ONCE(next->locked, 1); return; -- 1.7.1