From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933266AbcI3Mp5 (ORCPT ); Fri, 30 Sep 2016 08:45:57 -0400 Received: from merlin.infradead.org ([205.233.59.134]:50776 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932673AbcI3Mpt (ORCPT ); Fri, 30 Sep 2016 08:45:49 -0400 Date: Fri, 30 Sep 2016 14:45:42 +0200 From: Peter Zijlstra To: "Paul E. McKenney" 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 Message-ID: <20160930124542.GX5012@twins.programming.kicks-ass.net> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160930121721.GP14933@linux.vnet.ibm.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 :-)