From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1753205AbdK3QjU (ORCPT <rfc822;w@1wt.eu>);
        Thu, 30 Nov 2017 11:39:20 -0500
Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:37240 "EHLO
        mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL)
        by vger.kernel.org with ESMTP id S1752820AbdK3QjR (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 30 Nov 2017 11:39:17 -0500
Date: Thu, 30 Nov 2017 08:39:09 -0800
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Alan Stern <stern@rowland.harvard.edu>,
        Daniel Lustig <dlustig@nvidia.com>,
        Andrea Parri <parri.andrea@gmail.com>,
        Luc Maranget <luc.maranget@inria.fr>,
        Jade Alglave <j.alglave@ucl.ac.uk>, Boqun Feng <boqun.feng@gmail.com>,
        Nicholas Piggin <npiggin@gmail.com>, Will Deacon <will.deacon@arm.com>,
        David Howells <dhowells@redhat.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Kernel development list <linux-kernel@vger.kernel.org>
Subject: Re: Unlock-lock questions and the Linux Kernel Memory Model
Reply-To: paulmck@linux.vnet.ibm.com
References: <6b068a40-75bb-4152-b1ec-9ef3beacbdd5@nvidia.com>
 <Pine.LNX.4.44L0.1711301017130.1380-100000@iolanthe.rowland.org>
 <20171130161401.GP3624@linux.vnet.ibm.com>
 <20171130162501.cx5ha7nispozlf34@hirez.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20171130162501.cx5ha7nispozlf34@hirez.programming.kicks-ass.net>
User-Agent: Mutt/1.5.21 (2010-09-15)
X-TM-AS-GCONF: 00
x-cbid: 17113016-0024-0000-0000-000002FAB07C
X-IBM-SpamModules-Scores: 
X-IBM-SpamModules-Versions: BY=3.00008128; HX=3.00000241; KW=3.00000007;
 PH=3.00000004; SC=3.00000242; SDB=6.00953455; UDB=6.00481759; IPR=6.00733530;
 BA=6.00005722; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000;
 ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00018269; XFM=3.00000015;
 UTC=2017-11-30 16:39:13
X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused
x-cbparentid: 17113016-0025-0000-0000-0000462F06C9
Message-Id: <20171130163909.GQ3624@linux.vnet.ibm.com>
X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-11-30_05:,,
 signatures=0
X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501
 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0
 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0
 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000
 definitions=main-1711300217
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, Nov 30, 2017 at 05:25:01PM +0100, Peter Zijlstra wrote:
> On Thu, Nov 30, 2017 at 08:14:01AM -0800, Paul E. McKenney wrote:
> > > (Also, technically speaking, the litmus test doesn't have any release 
> > > operations, so no release sequence...)
> > 
> > True!  But if you translated it into C11, you would probably turn the
> > smp_wmb() followed by write into a store release, which would get you
> > a release sequence.
> 
> 	smp_wmb()
> 	WRITE_ONCE(*y, 1);
> 
> does not a RELEASE make.

Agreed, but it also does not C11 make.  There is no pure write barrier
in C11.

							Thanx, Paul