Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755470AbaFSNbK (ORCPT ); Thu, 19 Jun 2014 09:31:10 -0400 Received: from mail-qc0-f176.google.com ([209.85.216.176]:56272 "EHLO mail-qc0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753506AbaFSNbI (ORCPT ); Thu, 19 Jun 2014 09:31:08 -0400 Date: Thu, 19 Jun 2014 09:31:04 -0400 From: Tejun Heo To: Lai Jiangshan Cc: cl@linux-foundation.org, kmo@daterainc.com, linux-kernel@vger.kernel.org, "Paul E. McKenney" Subject: Re: [PATCH v2 6/6] percpu-refcount: implement percpu_ref_reinit() and percpu_ref_is_zero() Message-ID: <20140619133104.GH11042@htj.dyndns.org> References: <1403053685-28240-1-git-send-email-tj@kernel.org> <1403053685-28240-7-git-send-email-tj@kernel.org> <20140619022055.GD20100@mtj.dyndns.org> <53A25286.1030003@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53A25286.1030003@cn.fujitsu.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 19, 2014 at 11:01:26AM +0800, Lai Jiangshan wrote: > > + /* > > + * Restore per-cpu operation. smp_store_release() is paired with > > + * smp_load_acquire() in __pcpu_ref_alive() and guarantees that the > > s/smp_load_acquire()/smp_read_barrier_depends()/ Will update. > s/smp_store_release()/smp_mb()/ if you accept my next comment. > > > + * zeroing is visible to all percpu accesses which can see the > > + * following PCPU_REF_DEAD clearing. > > + */ > > + for_each_possible_cpu(cpu) > > + *per_cpu_ptr(pcpu_count, cpu) = 0; > > + > > + smp_store_release(&ref->pcpu_count_ptr, > > + ref->pcpu_count_ptr & ~PCPU_REF_DEAD); > > I think it would be better if smp_mb() is used. smp_wmb() would be better here. We don't need the reader side. > it is documented that smp_read_barrier_depends() and smp_mb() are paired. > Not smp_read_barrier_depends() and smp_store_release(). I don't know. I thought about doing that but the RCU accessors are pairing store_release with read_barrier_depends, so I don't think the particular paring is problematic and store_release is better at documenting what's being barriered. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/