From mboxrd@z Thu Jan 1 00:00:00 1970 From: Davidlohr Bueso Subject: Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper acquire/release barrier Date: Wed, 15 Jun 2016 09:56:59 -0700 Message-ID: <20160615165659.GC2094@linux-80c1.suse> References: <1465944489-43440-1-git-send-email-Waiman.Long@hpe.com> <1465944489-43440-2-git-send-email-Waiman.Long@hpe.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Return-path: Content-Disposition: inline In-Reply-To: <1465944489-43440-2-git-send-email-Waiman.Long@hpe.com> Sender: linux-kernel-owner@vger.kernel.org List-Archive: List-Post: To: Waiman Long Cc: Peter Zijlstra , Ingo Molnar , 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, Jason Low , Dave Chinner , Scott J Norton , Douglas Hatch List-ID: On Tue, 14 Jun 2016, Waiman Long wrote: >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. > >Signed-off-by: Waiman Long >--- > kernel/locking/osq_lock.c | 4 ++-- > 1 files changed, 2 insertions(+), 2 deletions(-) > >diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c >index 05a3785..7dd4ee5 100644 >--- a/kernel/locking/osq_lock.c >+++ b/kernel/locking/osq_lock.c >@@ -115,7 +115,7 @@ bool osq_lock(struct optimistic_spin_queue *lock) > * cmpxchg in an attempt to undo our queueing. > */ > >- while (!READ_ONCE(node->locked)) { >+ while (!smp_load_acquire(&node->locked)) { Hmm this being a polling path, that barrier can get pretty expensive and last I checked it was unnecessary: 036cc30c6b6 (locking/osq: No need for load/acquire when acquire-polling) Thanks, Davidlohr