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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6E421C76196 for ; Thu, 6 Apr 2023 18:23:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239543AbjDFSXh (ORCPT ); Thu, 6 Apr 2023 14:23:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39410 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229764AbjDFSXf (ORCPT ); Thu, 6 Apr 2023 14:23:35 -0400 Received: from mail-oi1-x22c.google.com (mail-oi1-x22c.google.com [IPv6:2607:f8b0:4864:20::22c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D182959F9 for ; Thu, 6 Apr 2023 11:23:33 -0700 (PDT) Received: by mail-oi1-x22c.google.com with SMTP id bi31so29690837oib.9 for ; Thu, 06 Apr 2023 11:23:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; t=1680805413; x=1683397413; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :sender:from:to:cc:subject:date:message-id:reply-to; bh=pighxnNX/pMr8ZJCiJ5Ab8VkADN3PXqDCYexnTC1HBY=; b=KzwA5MOSWigBpiX5qN7AVADQyzSShWXSvMzfkugV2wpO4KhIwWNcwSyAAlt9KjIPJA PMVqTIuZ49R6FpqY6q8VfI0L/2XwPFJB2DOFM9ru0JOocwZ+RcO1lsArgpgdOmvbZd6B e4krku/rrHgx+FwRdxEnqpXufcXWiifx1bG5qE2RMRGKOGR83NXtvR98SUbohrcavv0f EmX86JXWV4i3DVDD+539SvICvp1iz2EATHLfsRSVuY3RDuOazQfAj1hOIfsMQzhSp3EV UCsMqIfhrfU19zacTsqIvgCzLDJOdmwaE2KNP4qD9/8opQAOYBact/OnUHtG5xwaQ5ol VQYg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680805413; x=1683397413; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :sender:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=pighxnNX/pMr8ZJCiJ5Ab8VkADN3PXqDCYexnTC1HBY=; b=iJBYKDQXn3UZUg6F4Tw91aMcIDjkPvurTAf++XYcsVTTn2vp+qXwIuzJqFltISc+2i Dl7e+oyaOFx8jipnFyZRNNyrqhdN9ZUEGm1bKiUI0Ey3jdVcu/Pe1rxqlAwciBz4Tp8a ISYKRTifb8j3/dpkfNqTFrQgUMlypVURZp8aWdY+I7QCHL7w4DkIx0N64Cya7U5LIN3G jx/sfDnmxaVyg6BJ0w1nVingGHNNRI9SVv5nzsTHUNCZb201fKVfJSVRu1OveK+O29cK m+6HABGg2LWaDKUPLCHFNctYdAKKhqEjBxxcLrfy3cqZL/1HEZfqq1vR9d25g4CpzVpV UDhA== X-Gm-Message-State: AAQBX9fWTNJ6Wo3CC2f5GqPWLnhrgS5lC0xZAW0wHO6SdBo9lr3bp21B 6aXXohU68zDPmhi9l8iV3EHtJydbgRQ= X-Google-Smtp-Source: AKy350bC2J/KFajezUAsS5F6dp3T13DRhm78UZwA4zRmhcplWGX6uFAK1u8kN3TOj65gpxx9fON2dg== X-Received: by 2002:a05:6808:1396:b0:386:c879:d3ae with SMTP id c22-20020a056808139600b00386c879d3aemr4743399oiw.10.1680805413044; Thu, 06 Apr 2023 11:23:33 -0700 (PDT) Received: from ?IPV6:2600:1700:e321:62f0:329c:23ff:fee3:9d7c? ([2600:1700:e321:62f0:329c:23ff:fee3:9d7c]) by smtp.gmail.com with ESMTPSA id a6-20020a056808120600b003874631e249sm944134oil.36.2023.04.06.11.23.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 06 Apr 2023 11:23:32 -0700 (PDT) Sender: Guenter Roeck Message-ID: <1ed73bf7-809f-74e8-559d-e240a2a291c8@roeck-us.net> Date: Thu, 6 Apr 2023 11:23:30 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [PATCH] mm-treewide-redefine-max_order-sanely-fix.txt Content-Language: en-US To: "Kirill A. Shutemov" , Mike Rapoport Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <9460377a-38aa-4f39-ad57-fb73725f92db@roeck-us.net> <20230406072529.vupqyrzqnhyozeyh@box.shutemov.name> <83e6bc46-dfc0-0e95-e69c-5b996af1e50b@roeck-us.net> <20230406151015.yndcm24fyxitvqyc@box.shutemov.name> From: Guenter Roeck In-Reply-To: <20230406151015.yndcm24fyxitvqyc@box.shutemov.name> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/6/23 08:10, Kirill A. Shutemov wrote: > On Thu, Apr 06, 2023 at 06:57:41AM -0700, Guenter Roeck wrote: >> On 4/6/23 00:25, Kirill A. Shutemov wrote: >>> On Wed, Apr 05, 2023 at 10:20:26PM -0700, Guenter Roeck wrote: >>>> Hi, >>>> >>>> On Wed, Mar 15, 2023 at 06:38:00PM +0300, Kirill A. Shutemov wrote: >>>>> fix min() warning >>>>> >>>>> Link: https://lkml.kernel.org/r/20230315153800.32wib3n5rickolvh@box >>>>> Reported-by: kernel test robot >>>>> Link: https://lore.kernel.org/oe-kbuild-all/202303152343.D93IbJmn-lkp@intel.com/ >>>>> Signed-off-by: "Kirill A. Shutemov" >>>>> Cc: "Kirill A. Shutemov" >>>>> Cc: Zi Yan >>>>> Signed-off-by: Andrew Morton >>>> >>>> This patch results in various boot failures (hang) on arm targets >>>> in linux-next. Debug messages reveal the reason. >>>> >>>> ########### MAX_ORDER=10 start=0 __ffs(start)=-1 min()=10 min_t=-1 >>>> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ >>>> >>>> If start==0, __ffs(start) returns 0xfffffff or (as int) -1, which min_t() >>>> interprets as such, while min() apparently uses the returned unsigned long >>>> value. Obviously a negative order isn't received well by the rest of the >>>> code. >>> >>> Actually, __ffs() is not defined for 0. >>> >>> Maybe something like this? >>> >>> diff --git a/mm/memblock.c b/mm/memblock.c >>> index 7911224b1ed3..63603b943bd0 100644 >>> --- a/mm/memblock.c >>> +++ b/mm/memblock.c >>> @@ -2043,7 +2043,11 @@ static void __init __free_pages_memory(unsigned long start, unsigned long end) >>> int order; >>> while (start < end) { >>> - order = min_t(int, MAX_ORDER, __ffs(start)); >>> + /* __ffs() behaviour is undefined for 0 */ >>> + if (start) >>> + order = min_t(int, MAX_ORDER, __ffs(start)); >>> + else >>> + order = MAX_ORDER; >> >> Shouldn't that be >> else >> order = 0; >> ? > > +Mike. > > No. start == 0 is MAX_ORDER-aligned. We want to free the pages in the > largest chunks alignment allows. > Ah, ok. Makes sense. Thanks, Guenter