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,DKIM_SIGNED, DKIM_VALID,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 238ABC433E1 for ; Tue, 21 Jul 2020 22:58:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E94C720720 for ; Tue, 21 Jul 2020 22:58:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=gmx.net header.i=@gmx.net header.b="dXnaMdbw" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728092AbgGUW6s (ORCPT ); Tue, 21 Jul 2020 18:58:48 -0400 Received: from mout.gmx.net ([212.227.15.18]:56065 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726555AbgGUW6r (ORCPT ); Tue, 21 Jul 2020 18:58:47 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1595372323; bh=DyKo7ZHGl5liUSaw85fLhX1JG7toYiDUyfvOxs9oFcA=; h=X-UI-Sender-Class:Subject:To:References:From:Date:In-Reply-To; b=dXnaMdbwg2QcJtbm6SbafW9P/cETgNHIE7Tcw/iqx/mF1BF2ITeB7ecLYmmfr8CMp y2eUbYjQ5rJBoqBN1y0PH9kSQp+rbYAonopKErRTnYKLdLZXe4vY3P74XdtqZfwIKZ WJL6BTNZ92y17JZ1J91jmGcwZzUGs/o0e3hn/pyI= X-UI-Sender-Class: 01bb95c1-4bf8-414a-932a-4f6e2808ef9c Received: from [0.0.0.0] ([149.28.201.231]) by mail.gmx.com (mrgmx005 [212.227.17.184]) with ESMTPSA (Nemesis) id 1N6bk4-1ktnGm1NZm-0186jz; Wed, 22 Jul 2020 00:58:42 +0200 Subject: Re: [PATCH 1/2] btrfs-progs: convert: Prevent bit overflow for cctx->total_bytes To: dsterba@suse.cz, Qu Wenruo , linux-btrfs@vger.kernel.org, Christian Zangl References: <20200720125109.93970-1-wqu@suse.com> <20200720160945.GH3703@twin.jikos.cz> <20200721095826.GJ3703@twin.jikos.cz> <0d3eb6c1-f88a-e7cd-7d12-92bce0f2025c@suse.com> <20200721135533.GL3703@twin.jikos.cz> From: Qu Wenruo Autocrypt: addr=quwenruo.btrfs@gmx.com; prefer-encrypt=mutual; keydata= mQENBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB AAG0IlF1IFdlbnJ1byA8cXV3ZW5ydW8uYnRyZnNAZ214LmNvbT6JAVQEEwEIAD4CGwMFCwkI BwIGFQgJCgsCBBYCAwECHgECF4AWIQQt33LlpaVbqJ2qQuHCPZHzoSX+qAUCWdWCnQUJCWYC bgAKCRDCPZHzoSX+qAR8B/94VAsSNygx1C6dhb1u1Wp1Jr/lfO7QIOK/nf1PF0VpYjTQ2au8 ihf/RApTna31sVjBx3jzlmpy+lDoPdXwbI3Czx1PwDbdhAAjdRbvBmwM6cUWyqD+zjVm4RTG rFTPi3E7828YJ71Vpda2qghOYdnC45xCcjmHh8FwReLzsV2A6FtXsvd87bq6Iw2axOHVUax2 FGSbardMsHrya1dC2jF2R6n0uxaIc1bWGweYsq0LXvLcvjWH+zDgzYCUB0cfb+6Ib/ipSCYp 3i8BevMsTs62MOBmKz7til6Zdz0kkqDdSNOq8LgWGLOwUTqBh71+lqN2XBpTDu1eLZaNbxSI ilaVuQENBFnVga8BCACqU+th4Esy/c8BnvliFAjAfpzhI1wH76FD1MJPmAhA3DnX5JDORcga CbPEwhLj1xlwTgpeT+QfDmGJ5B5BlrrQFZVE1fChEjiJvyiSAO4yQPkrPVYTI7Xj34FnscPj /IrRUUka68MlHxPtFnAHr25VIuOS41lmYKYNwPNLRz9Ik6DmeTG3WJO2BQRNvXA0pXrJH1fN GSsRb+pKEKHKtL1803x71zQxCwLh+zLP1iXHVM5j8gX9zqupigQR/Cel2XPS44zWcDW8r7B0 q1eW4Jrv0x19p4P923voqn+joIAostyNTUjCeSrUdKth9jcdlam9X2DziA/DHDFfS5eq4fEv ABEBAAGJATwEGAEIACYCGwwWIQQt33LlpaVbqJ2qQuHCPZHzoSX+qAUCXZw1rgUJCWpOfwAK CRDCPZHzoSX+qFcEB/95cs8cM1OQdE/GgOfCGxwgckMeWyzOR7bkAWW0lDVp2hpgJuxBW/gy fmtBnUaifnggx3EE3ev8HTysZU9q0h+TJwwJKGv6sUc8qcTGFDtavnnl+r6xDUY7A6GvXEsS oCEEynby72byGeSovfq/4AWGNPBG1L61Exl+gbqfvbECP3ziXnob009+z9I4qXodHSYINfAk ZkA523JGap12LndJeLk3gfWNZfXEWyGnuciRGbqESkhIRav8ootsCIops/SqXm0/k+Kcl4gG UO/iD/T5oagaDh0QtOd8RWSMwLxwn8uIhpH84Q4X1LadJ5NCgGa6xPP5qqRuiC+9gZqbq4Nj Message-ID: Date: Wed, 22 Jul 2020 06:58:39 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200721135533.GL3703@twin.jikos.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable X-Provags-ID: V03:K1:xGFZMvEsT+BLImN2xvti2AOz05otyfs1v+zy9RtjVNBXVosi6Lc R1C3jmEjWH3ElfVS5HtWl3LidoSEM3jC8BgVHzHhjXQ0Jnrlgu/xjewq6v7RVAjNfVVrltl oYwbgtqSeAAkOYe1/oSQ/bQBtlL1Ky82hUpDkw7vOP/Zobf5/ITZSO7TLsQA9WEJb60lVq3 CDNv/ufFBCmh9/hjWl8ag== X-UI-Out-Filterresults: notjunk:1;V03:K0:VPTgejeGmZQ=:qknFoi9WfKuxcOp4lVBhs1 ymnCcAB/VnY0XxyrIxfh+gcfbjl247LQ5i6aNMs2lGuFFQKGo+D7woNxbN84VGLiBf0BT0GD9 Za2S1MFFTh0cuCjY3hhdfSiIJrwuAgVYe8qeBHqRgwroQwMXx/AEtBH1EmY6wyT7cQ1VNwC8A ZXvhMjr3Dtpy2NCdzWS9p4IzbcgCgkxYPsdd85WPZgBZ+8FemgmK3T2mm+PZ37f2rCCUZBM7Z elyAdMUAI688cTkaEdoLh4/LUlNlW/hvw836yF7igeWKTFEGYjP0waO+g77vrWucUXvqJFiTf o8pxW0Sm9kPX40c1Q80mbw2+poCyKahchn8CuvRfBXJZNUpvR/uxZwMk4LWv6olriTZt5rPBv hF0fuCzw8/A6KWDKmYFJM+Fionxajl0TGC87imBvmf7bdghitZtSYGSvH7C2mprekIbVtFESU HXfII82kNH7DL7M5seu845LAxY/uTuYWcCkUVgh8NmmpUnVljmD5QiCiGnKKsDfy19XRgMHXM pfj6R3sSqZqCKcCZSyiFckEij0JENSIKeLq9BSn48dN0Ne8hivc1eO1tZ9W6im+1PQO7faMwV dUd035Uh3aE97Oq3pf1k3YXgZYtvnwj+NbQWHmT3cTpYGnW7kijwK8KiUlldX/Us8qACXO4py lc21Fv/H2ypHd3Vu08MUsIwpsLuFyn0L4F3a9VCve0FRMet/PBfQTrQkjgwekXAqBlTQd6lJ4 Ugj7O8GlJ9sJQ4o2F5MmX/TY7h29OVHYZHhiy6r7DcFfOGiX2yVNfPGfX+kpNxHHt9HlYhFe/ k2Qv9LNHzEFFmTO2XnJudwRNcU/XVFRgcbRYoAg2Qf0eIuapzBvTFIHTCzJpR//iv7sKCTCjE 6xyh23XUQjdNNrgPXmfyhMYSrtC97CtfFQFPNhEolgD9/Rw6vadRVME9HBkmP6jEzRmnDcq/b 3J4YJcDPVnHzrZrJjM9SEMvlFS6zwPupz8x9ON08hKx43jhVQVE7dqSPnEMFo9iva5RdMXZHz I2gpXjDAPBU1dy/e5TjNTA+az9ItbtPvLingNrVECSRQ09LIfSzfToHF+vbyVnkwsbB8mqB2L YMKGwL9knhnDcBDezvdJcZCLm8NzKP864FjrJz9OtQS79Q20rMOra6IX9A/luHjohaSkFqNnS VK1Xu8PrX4cr+Zd7c2a0L0ei3Q6uZObSidDzVTdkI15LGY3FiRKjFtbmZcfOM+zTZBKlK2h6v 6IL0T2cYRXjn/7K7U8XbMd7aorMx5OxpJ2N40HQ== Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 2020/7/21 =E4=B8=8B=E5=8D=889:55, David Sterba wrote: > On Tue, Jul 21, 2020 at 06:29:31PM +0800, Qu Wenruo wrote: >> On 2020/7/21 =E4=B8=8B=E5=8D=885:58, David Sterba wrote: >>> On Tue, Jul 21, 2020 at 07:51:00AM +0800, Qu Wenruo wrote: >>>> >>>> >>>> On 2020/7/21 =E4=B8=8A=E5=8D=8812:09, David Sterba wrote: >>>>> On Mon, Jul 20, 2020 at 08:51:08PM +0800, Qu Wenruo wrote: >>>>>> --- a/convert/source-ext2.c >>>>>> +++ b/convert/source-ext2.c >>>>>> @@ -87,7 +87,8 @@ static int ext2_open_fs(struct btrfs_convert_cont= ext *cctx, const char *name) >>>>>> cctx->fs_data =3D ext2_fs; >>>>>> cctx->blocksize =3D ext2_fs->blocksize; >>>>>> cctx->block_count =3D ext2_fs->super->s_blocks_count; >>>>>> - cctx->total_bytes =3D ext2_fs->blocksize * ext2_fs->super->s_bloc= ks_count; >>>>>> + cctx->total_bytes =3D (u64)ext2_fs->blocksize * >>>>>> + (u64)ext2_fs->super->s_blocks_count; >>>>> >>>>> Do you need to cast both? Once one of the types is wide enough for t= he >>>>> result, there should be no loss. >>>>> >>>> I just want to be extra safe. >>> >>> Typecasts in code raise questions why are they needed, 'to be extra' >>> safe is not a good reason. One typecast in multiplication/shifts is a >>> common pattern to widen the result but two look more like lack of >>> understanding of the integer promotion rules. >> >> My point here is, I don't want the reviewers or new contributors to >> bother about the promotion rules at all. > > Ouch, I hope you don't mean that contributors should ignore the trickier > parts of C language. Especially reviewers _have_ to bother about all > sorts of subtle behaviour. > >> They only need to know that using blocksize and blocks_count directly t= o >> do multiply would lead to overflow. >> >> Other details like whether the multiply follows the highest factor or >> the left operator or the right operator, shouldn't be the point and we >> don't really need to bother. > > ... and introduce bugs? > >> Thus casting both would definitely be right, without the need to refer >> to the complex rule book, thus save the reviewer several minutes. > > The opposite, if you send me code that's not following known schemes or > idiomatic schemes I'll be highly suspicious and looking for the reasons > why it's that way and making sure it's correct costs way more time. > OK, then would you please remove one casting at merge time, or do I need to resend? Thanks, Qu