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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS 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 2003BC433DB for ; Tue, 2 Mar 2021 12:28:35 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8F7C364F7A for ; Tue, 2 Mar 2021 12:28:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8F7C364F7A Authentication-Results: mail.kernel.org; dmarc=pass (p=none dis=none) header.from=xenproject.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.92322.174202 (Exim 4.92) (envelope-from ) id 1lH48Q-0006YE-33; Tue, 02 Mar 2021 12:28:18 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 92322.174202; Tue, 02 Mar 2021 12:28:18 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lH48Q-0006Y7-04; Tue, 02 Mar 2021 12:28:18 +0000 Received: by outflank-mailman (input) for mailman id 92322; Tue, 02 Mar 2021 12:28:16 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lH48O-0006Y2-D3 for xen-devel@lists.xenproject.org; Tue, 02 Mar 2021 12:28:16 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lH48O-0004SU-8i for xen-devel@lists.xenproject.org; Tue, 02 Mar 2021 12:28:16 +0000 Received: from iwj (helo=mariner.uk.xensource.com) by xenbits.xenproject.org with local-bsmtp (Exim 4.92) (envelope-from ) id 1lH48O-0002ZY-7W for xen-devel@lists.xenproject.org; Tue, 02 Mar 2021 12:28:16 +0000 Received: from iwj by mariner.uk.xensource.com with local (Exim 4.89) (envelope-from ) id 1lH48K-0007Q3-UP; Tue, 02 Mar 2021 12:28:12 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xenproject.org; s=20200302mail; h=References:In-Reply-To:Subject:Cc:To:Date :Message-ID:Content-Transfer-Encoding:Content-Type:MIME-Version:From; bh=qYeYni0fVxOwJMUANxe21QD/smSLcjBLuyfubwGjUUg=; b=rNrK90XRZMxIfrYr5XtoilNAzw AOrnQqC9Q0G90oIHob3IlIo4I2fBLCyKdHQfCcv/PqEEP+0jl4SQTdp9IbNKY4Di8lSNjITFESUMA wy8wrq6d1s8L0tlAmTPhXqmH2iBT65H/bMpAPu/8WZjGF3rvSILW779DuxJFaVuR4Utk=; From: Ian Jackson MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <24638.12124.687863.290191@mariner.uk.xensource.com> Date: Tue, 2 Mar 2021 12:28:12 +0000 To: Jan Beulich Cc: "xen-devel\@lists.xenproject.org" , Andrew Cooper , Wei Liu , Roger Pau =?iso-8859-1?Q?Monn=E9?= , George Dunlap Subject: Re: [PATCH 2/2][4.15?] x86: fix build when NR_CPUS == 1 In-Reply-To: <7b4c0c51-5a3c-b9bb-7c9c-62285095183b@suse.com> References: <1d8d5089-32a9-9c42-5949-8f9cd20f33e0@suse.com> <24637.4165.400955.400473@mariner.uk.xensource.com> <7b4c0c51-5a3c-b9bb-7c9c-62285095183b@suse.com> X-Mailer: VM 8.2.0b under 24.5.1 (i686-pc-linux-gnu) Jan Beulich writes ("Re: [PATCH 2/2][4.15?] x86: fix build when NR_CPUS == 1"): > On 01.03.2021 17:03, Ian Jackson wrote: > > Jan Beulich writes ("[PATCH 2/2][4.15?] x86: fix build when NR_CPUS == 1"): > >> In this case the compiler is recognizing that no valid array indexes > >> remain (in x2apic_cluster()'s access to per_cpu(cpu_2_logical_apicid, > >> ...)), but oddly enough isn't really consistent about the checking it > >> does (see the code comment). > > ... > >> - if (this_cpu == cpu || x2apic_cluster(this_cpu) != x2apic_cluster(cpu)) > >> + if ( this_cpu == cpu ) > >> + continue; > >> + /* > >> + * Guard in particular against the compiler suspecting out-of-bounds > >> + * array accesses below when NR_CPUS=1 (oddly enough with gcc 10 it > >> + * is the 1st of these alone which actually helps, not the 2nd, nor > >> + * are both required together there). > >> + */ > >> + BUG_ON(this_cpu >= NR_CPUS); > >> + BUG_ON(cpu >= NR_CPUS); > >> + if ( x2apic_cluster(this_cpu) != x2apic_cluster(cpu) ) > >> continue; > > > > Is there some particular reason for not putting the BUG_ON before the > > if test ? That would avoid the refactoring. > > I want it to be as close as possible to the place where the issue > is. I also view the refactoring as a good thing, since it allows > a style correction as a side effect. I'm afraid that at this stage of the release I would prefer changes to be as small as reasonably sensible. So unless there is some reason, other than taste, style or formatting, could we please just introduce the new BUG_ON and not also do other refactoring. Ian.