From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0F7C0C433E6 for ; Thu, 7 Jan 2021 17:45:17 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 89FCD233FB for ; Thu, 7 Jan 2021 17:45:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 89FCD233FB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id E11C36B0193; Thu, 7 Jan 2021 12:45:15 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id DBF5F6B0194; Thu, 7 Jan 2021 12:45:15 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C88416B0195; Thu, 7 Jan 2021 12:45:15 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0018.hostedemail.com [216.40.44.18]) by kanga.kvack.org (Postfix) with ESMTP id ABFB36B0193 for ; Thu, 7 Jan 2021 12:45:15 -0500 (EST) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 6BF0C180AD811 for ; Thu, 7 Jan 2021 17:45:15 +0000 (UTC) X-FDA: 77679705390.15.talk17_3d0722a274ec Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin15.hostedemail.com (Postfix) with ESMTP id 3DF4F1814B0C9 for ; Thu, 7 Jan 2021 17:45:15 +0000 (UTC) X-HE-Tag: talk17_3d0722a274ec X-Filterd-Recvd-Size: 3049 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf19.hostedemail.com (Postfix) with ESMTP for ; Thu, 7 Jan 2021 17:45:14 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 3E703AD78; Thu, 7 Jan 2021 17:45:13 +0000 (UTC) To: Andrea Arcangeli Cc: Hugh Dickins , Andrew Morton , Alex Shi , Minchan Kim , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1607743586-80303-1-git-send-email-alex.shi@linux.alibaba.com> <1607743586-80303-2-git-send-email-alex.shi@linux.alibaba.com> <20210106114620.5c221690f3a9cad7afcc3077@linux-foundation.org> From: Vlastimil Babka Subject: Re: [PATCH] mm/mmap: replace if (cond) BUG() with BUG_ON() Message-ID: Date: Thu, 7 Jan 2021 18:45:12 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 1/7/21 6:36 PM, Andrea Arcangeli wrote: > On Thu, Jan 07, 2021 at 06:28:29PM +0100, Vlastimil Babka wrote: >> On 1/6/21 9:18 PM, Hugh Dickins wrote: >> > On Wed, 6 Jan 2021, Andrea Arcangeli wrote: >> >>=20 >> >> I'd be surprised if the kernel can boot with BUG_ON() defined as "d= o >> >> {}while(0)" so I guess it doesn't make any difference. >> >=20 >> > I had been afraid of that too, when CONFIG_BUG is not set: >> > but I think it's actually "if (cond) do {} while (0)". >>=20 >> It's a maze of configs and arch-specific vs generic headers, but I do = see this >> in include/asm-generic/bug.h: >>=20 >> #else /* !CONFIG_BUG */ >> #ifndef HAVE_ARCH_BUG >> #define BUG() do {} while (1) >> #endif >>=20 >> So seems to me there *are* configurations possible where side-effects = are indeed >> thrown away, right? >=20 > But this not BUG_ON,=20 Oh, you're right, I got lost in the maze. > and that is an infinite loop while(1), not an And I overlooked that "1" too. So that AFAICS means *both* VM_BUG_ON and VM_WARN_ON behave differently w= rt side-effects when disabled than BUG_ON and WARN_ON. > optimization away as in while (0) that I was suggesting to just throw > away cond and make it a noop. BUG() is actually the thing to use to > move functional stuff out of BUG_ON so it's not going to be causing > issues if it just loops. >=20 > This overall feels mostly an aesthetically issue. >=20 > Thanks, > Andrea >=20