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=-0.5 required=3.0 tests=FREEMAIL_FORGED_FROMDOMAIN, FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 8476AECDE43 for ; Fri, 19 Oct 2018 13:03:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3885720644 for ; Fri, 19 Oct 2018 13:03:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3885720644 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=gmx.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-btrfs-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727426AbeJSVJ0 (ORCPT ); Fri, 19 Oct 2018 17:09:26 -0400 Received: from mout.gmx.net ([212.227.17.22]:57225 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727336AbeJSVJZ (ORCPT ); Fri, 19 Oct 2018 17:09:25 -0400 Received: from [0.0.0.0] ([210.140.77.29]) by mail.gmx.com (mrgmx102 [212.227.17.174]) with ESMTPSA (Nemesis) id 0MSY2q-1g5kgw0Bwi-00RXNd; Fri, 19 Oct 2018 15:03:15 +0200 Received: from [0.0.0.0] ([210.140.77.29]) by mail.gmx.com (mrgmx102 [212.227.17.174]) with ESMTPSA (Nemesis) id 0MSY2q-1g5kgw0Bwi-00RXNd; Fri, 19 Oct 2018 15:03:15 +0200 Subject: Re: [PATCH 4/6] btrfs: qgroup: Introduce per-root swapped blocks infrastructure To: dsterba@suse.cz, Qu Wenruo , Qu Wenruo , linux-btrfs@vger.kernel.org References: <20181018111729.11128-1-wqu@suse.com> <20181018111729.11128-5-wqu@suse.com> <20181018162059.GJ29418@twin.jikos.cz> <20181019091516.GB16290@twin.jikos.cz> <63697e20-9c39-da22-437d-b43612f25d3c@suse.de> <20181019100419.GC16290@twin.jikos.cz> From: Qu Wenruo Openpgp: preference=signencrypt Autocrypt: addr=quwenruo.btrfs@gmx.com; prefer-encrypt=mutual; keydata= xsBNBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB AAHNIlF1IFdlbnJ1byA8cXV3ZW5ydW8uYnRyZnNAZ214LmNvbT7CwJQEEwEIAD4CGwMFCwkI BwIGFQgJCgsCBBYCAwECHgECF4AWIQQt33LlpaVbqJ2qQuHCPZHzoSX+qAUCWdWCnQUJCWYC bgAKCRDCPZHzoSX+qAR8B/94VAsSNygx1C6dhb1u1Wp1Jr/lfO7QIOK/nf1PF0VpYjTQ2au8 ihf/RApTna31sVjBx3jzlmpy+lDoPdXwbI3Czx1PwDbdhAAjdRbvBmwM6cUWyqD+zjVm4RTG rFTPi3E7828YJ71Vpda2qghOYdnC45xCcjmHh8FwReLzsV2A6FtXsvd87bq6Iw2axOHVUax2 FGSbardMsHrya1dC2jF2R6n0uxaIc1bWGweYsq0LXvLcvjWH+zDgzYCUB0cfb+6Ib/ipSCYp 3i8BevMsTs62MOBmKz7til6Zdz0kkqDdSNOq8LgWGLOwUTqBh71+lqN2XBpTDu1eLZaNbxSI ilaVzsBNBFnVga8BCACqU+th4Esy/c8BnvliFAjAfpzhI1wH76FD1MJPmAhA3DnX5JDORcga CbPEwhLj1xlwTgpeT+QfDmGJ5B5BlrrQFZVE1fChEjiJvyiSAO4yQPkrPVYTI7Xj34FnscPj /IrRUUka68MlHxPtFnAHr25VIuOS41lmYKYNwPNLRz9Ik6DmeTG3WJO2BQRNvXA0pXrJH1fN GSsRb+pKEKHKtL1803x71zQxCwLh+zLP1iXHVM5j8gX9zqupigQR/Cel2XPS44zWcDW8r7B0 q1eW4Jrv0x19p4P923voqn+joIAostyNTUjCeSrUdKth9jcdlam9X2DziA/DHDFfS5eq4fEv ABEBAAHCwHwEGAEIACYWIQQt33LlpaVbqJ2qQuHCPZHzoSX+qAUCWdWBrwIbDAUJA8JnAAAK CRDCPZHzoSX+qA3xB/4zS8zYh3Cbm3FllKz7+RKBw/ETBibFSKedQkbJzRlZhBc+XRwF61mi f0SXSdqKMbM1a98fEg8H5kV6GTo62BzvynVrf/FyT+zWbIVEuuZttMk2gWLIvbmWNyrQnzPl mnjK4AEvZGIt1pk+3+N/CMEfAZH5Aqnp0PaoytRZ/1vtMXNgMxlfNnb96giC3KMR6U0E+siA 4V7biIoyNoaN33t8m5FwEwd2FQDG9dAXWhG13zcm9gnk63BN3wyCQR+X5+jsfBaS4dvNzvQv h8Uq/YGjCoV1ofKYh3WKMY8avjq25nlrhzD/Nto9jHp8niwr21K//pXVA81R2qaXqGbql+zo Message-ID: <5684c607-0b73-3fa7-0e8e-003fbecf2cf8@gmx.com> Date: Fri, 19 Oct 2018 21:03:08 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20181019100419.GC16290@twin.jikos.cz> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="twHviTAXYf0XmNWnteCQ4Cr63AaDtjwsS" X-Provags-ID: V03:K1:XG9jq0XqoItN0NurbCZb1yl+6sBRN+RTey1cRBDz9mX5yXK1Txp ziYc2RBJQyr1KLgnNfpgq6gGNuBD7craEIuti+nTcWorzJOxuEhLUrx1MpfsBHl0RHCFJNr 3lQGooJZSWwvgvfC5Xmu9FXPizeJ8flrGjFiAlSb3fuElX6y9FMfISuGbZJZO/DKN5toVym 8sc2caDQHbUCcQlo8t7Wg== X-UI-Out-Filterresults: notjunk:1;V01:K0:3BvXLec9BRI=:g0hFh4st+uiOA/noeczRNa AmIXwprIUPNdGYCsFyYbhRh8Vu8Yu+GNfAZlaM2gyEAVvmuscvIGMG9KQnXJQdKD3lYhA2y2b RBSmLSmya+JpuVt/UTDHAqZTLEIsQPL8G6bp2tB6PbFuloTKDlTBACBTZ34R6jUv0YUZmwEc8 79MHcsBjMc36Rk/OWipCWzmCRo29lEku9fa3+MV6fCfJ63q/2FhZ1yzK7GSj2FV7eZO0CCPiv fM+rXQ4Hjatt+tmT078t9+EciQQugh2TBN+tyOF5A0SGT5VLTyi/zvL0YAREmyqLUhmgZHXaV uMxFvjPEdIn+Jw4qq5iYMSWhCdCpDIaGLNk3+Z5qTq36cqkll/F7q/uJ1EJllNpO0XCECbVe0 Fan/GivbTdYqZr1MIr9WDuwufecIMOgOqVzqn4CjVJ1kA1h/LhtXQKzdxZYFSTVu6K636Spln L5xtaZb8xtBE9zfhaqmZsKVXNnpdZEswaijSks6giwNtKD7JWeEXYoRQz+fmgwlj7KqxKNLKn xGmU98kGwuwoSuv4xu2f7tKO+8GKt7WOyg6Na+xoFGaN96i5ToInbo/8ErmCa7i3vTOsYzchs SA9iuCIs2WcOiCFtGgwwdQkYsHf5chfNM25Vm9PxlfYsVgs7bcimIxo2ThdQwbf47SCLRQCCm txCbVIhaJ31JMRXI+arbcXSqNdiIbiSIMfXw/WjbZpZ73BaAhSGZKGEOIwIQz2Mm6nfdroxBM tZeWHTl9SCXW+7AKNudIlqJGI9ohql/qpUdiNGE8nVEGzIYE+iwGer9mUPmatkBYNLgwe6ubg gGEJeXjppZIUqV6+u/b3T7NJD9ZyQ== Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --twHviTAXYf0XmNWnteCQ4Cr63AaDtjwsS Content-Type: multipart/mixed; boundary="qFcCxkVKPPLZnwBmXxxip0ujsaPZ8Elrp"; protected-headers="v1" From: Qu Wenruo To: dsterba@suse.cz, Qu Wenruo , Qu Wenruo , linux-btrfs@vger.kernel.org Message-ID: <5684c607-0b73-3fa7-0e8e-003fbecf2cf8@gmx.com> Subject: Re: [PATCH 4/6] btrfs: qgroup: Introduce per-root swapped blocks infrastructure References: <20181018111729.11128-1-wqu@suse.com> <20181018111729.11128-5-wqu@suse.com> <20181018162059.GJ29418@twin.jikos.cz> <20181019091516.GB16290@twin.jikos.cz> <63697e20-9c39-da22-437d-b43612f25d3c@suse.de> <20181019100419.GC16290@twin.jikos.cz> In-Reply-To: <20181019100419.GC16290@twin.jikos.cz> --qFcCxkVKPPLZnwBmXxxip0ujsaPZ8Elrp Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 2018/10/19 =E4=B8=8B=E5=8D=886:04, David Sterba wrote: > On Fri, Oct 19, 2018 at 05:46:28PM +0800, Qu Wenruo wrote: >> Did you mean some like this is possible? >> >> rbtree_postorder_for_each_entry_safe() { >> kfree(entry); >> } >> >> If so, I still don't really believe it's OK. >> >> For the following tree: >> 4 >> / \ >> 2 6 >> / \ / \ >> 1 3 5 7 >> >> If current entry is 2, next is 3. >> And 2 get freed. >> Then we go 3, to reach next we need to go back to access 2, which is >> already freed, we will trigger use-after-free. >> >> So the only correct way to free the whole rbtree is still that tried a= nd >> true while(rb_first()) loop. >> >> Or did I miss something? >=20 > It's postorder traversal so the node is ready for processing after all > it's children are processed. In the above example, it will result in th= e > followin sequence: 1 3 2 5 7 6 4 . Oh, I totally misunderstand the word post-order. Post-order is LRN, so upper nodes are always accessed last, then kfree() inside post-order is completely OK. Thanks, Qu >=20 > The iterator is safe in the sense that there's enough information saved= > before going to the node so it's not needed to be accessed later, eg. > after it's freed. >=20 > prelim_release uses the same postorder/kfree pattern. >=20 --qFcCxkVKPPLZnwBmXxxip0ujsaPZ8Elrp-- --twHviTAXYf0XmNWnteCQ4Cr63AaDtjwsS Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEELd9y5aWlW6idqkLhwj2R86El/qgFAlvJ1gwACgkQwj2R86El /qjA7Qf9Eq7kCL2VqsLRShTz5BMnG4qUf8YhjgfwsNAs8rbDumDz9FQQODrSM6jR +c3RPSCKyFcYqLyivc0sfSEkCKKhBPB5z/VMBoCjfb/WolJwNjFc2d+zU93TXCZX JRLSCfnidttlDqIJAc6+iEimtU+qKdIrclrCFKrD9mN1cHBwhkClvEnLQ0REcRXR aEHbKYLTJMn3SJSRLmeRgnih0BXrWDmeso8YqcXtrtho9IhMOqy/+tYYf4tHrcWE D5Njg05tD7Amu7ToIfi9JI100bGiSLI4UthfRCmqzFidatBJC2k7T3gPOgTSnZGi NeP8uQGzPaM8eGhbs+YSwvbmmRrlZw== =BO4W -----END PGP SIGNATURE----- --twHviTAXYf0XmNWnteCQ4Cr63AaDtjwsS--