From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933472AbcI3NKM (ORCPT ); Fri, 30 Sep 2016 09:10:12 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:48147 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932707AbcI3NKD (ORCPT ); Fri, 30 Sep 2016 09:10:03 -0400 Date: Fri, 30 Sep 2016 06:10:00 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Will Deacon , linux-kernel@vger.kernel.org, mingo@kernel.org, dhowells@redhat.com, stern@rowland.harvard.edu Subject: Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability Reply-To: paulmck@linux.vnet.ibm.com References: <20160929155401.GA5097@linux.vnet.ibm.com> <20160929155817.GB5016@twins.programming.kicks-ass.net> <20160929160307.GT13862@arm.com> <20160929164353.GX14933@linux.vnet.ibm.com> <20160930102516.GW5012@twins.programming.kicks-ass.net> <20160930121721.GP14933@linux.vnet.ibm.com> <20160930124542.GX5012@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160930124542.GX5012@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16093013-0004-0000-0000-00001081923C X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00005830; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000186; SDB=6.00763079; UDB=6.00363835; IPR=6.00538236; BA=6.00004774; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00012830; XFM=3.00000011; UTC=2016-09-30 13:10:00 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16093013-0005-0000-0000-00007958C406 Message-Id: <20160930131000.GQ14933@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-09-30_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1609280000 definitions=main-1609300238 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 30, 2016 at 02:45:42PM +0200, Peter Zijlstra wrote: > On Fri, Sep 30, 2016 at 05:17:21AM -0700, Paul E. McKenney wrote: > > On Fri, Sep 30, 2016 at 12:25:16PM +0200, Peter Zijlstra wrote: > > > > So its a pretty dumb thing to do in any case (and yes the kernel does > > > this). Its also entirely expected in my book, that if you generate > > > conflicting writes on a release, ordering is out the window. > > > > > > Why do we need to call this out? Who in his right mind would want to do > > > this and expect anything other than wreckage? > > > > > > Not that we're not having too much 'fun' discussing this,.. but I do > > > wonder why we need to call this out. > > > > You lost me on this one... If no one does this, sure, we can leave it out. > > But if some part of the kernel does rely on this, we should call it out as > > forbidden. And fix the kernel, of course. > > Well, the kernel does this, but doesn't rely on ordering. Do "git grep > zap_locks". Its disgusting, can (and does) fail and generally is a sign > of badly broken code (printk is all that). ;-) ;-) ;-) > > Or am I missing your point? > > My point was, its obvious crack, anybody doing this needs to have his > head examined. Then again, maybe we should just say that :-) I do find that as I get older, emphatically stating the obvious becomes an increasingly large fraction of my role, so agreed. ;-) Thanx, Paul