From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751351AbdEaPV4 (ORCPT ); Wed, 31 May 2017 11:21:56 -0400 Received: from mx2.suse.de ([195.135.220.15]:47435 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751011AbdEaPVy (ORCPT ); Wed, 31 May 2017 11:21:54 -0400 Date: Wed, 31 May 2017 17:21:51 +0200 From: Michal Hocko To: Nick Desaulniers Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, mgorman@techsingularity.net, vbabka@suse.cz, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [Patch v2] mm/vmscan: fix unsequenced modification and access warning Message-ID: <20170531152151.GT27783@dhcp22.suse.cz> References: <20170510071511.GA31466@dhcp22.suse.cz> <20170510082734.2055-1-nick.desaulniers@gmail.com> <20170510083844.GG31466@dhcp22.suse.cz> <20170516082746.GA2481@dhcp22.suse.cz> <20170526044343.autu63rpfigbzhyi@lostoracle.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170526044343.autu63rpfigbzhyi@lostoracle.net> 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 25-05-17 21:43:43, Nick Desaulniers wrote: > On Tue, May 16, 2017 at 10:27:46AM +0200, Michal Hocko wrote: > > I guess it is worth reporting this to clang bugzilla. Could you take > > care of that Nick? > > >From https://bugs.llvm.org//show_bug.cgi?id=33065#c5 > it seems that this is indeed a sequence bug in the previous version of > this code and not a compiler bug. You can read that response for the > properly-cited wording but my TL;DR/understanding is for the given code: > > struct foo bar = { > .a = (c = 0), > .b = c, > }; > > That the compiler is allowed to reorder the initializations of bar.a and > bar.b, so what the value of c here might not be what you expect. This is interesting because what I hear from our gcc people is something different. I am not in a possition to argue here, though. -- Michal Hocko SUSE Labs