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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 D071FECDE3D for ; Fri, 19 Oct 2018 09:46:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 83EF821476 for ; Fri, 19 Oct 2018 09:46:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 83EF821476 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.de 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 S1726968AbeJSRv4 (ORCPT ); Fri, 19 Oct 2018 13:51:56 -0400 Received: from mx2.suse.de ([195.135.220.15]:48980 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726903AbeJSRv4 (ORCPT ); Fri, 19 Oct 2018 13:51:56 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id C2C31AEB0; Fri, 19 Oct 2018 09:46:34 +0000 (UTC) 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> From: Qu Wenruo Openpgp: preference=signencrypt Autocrypt: addr=wqu@suse.de; 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: <63697e20-9c39-da22-437d-b43612f25d3c@suse.de> Date: Fri, 19 Oct 2018 17:46:28 +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: <20181019091516.GB16290@twin.jikos.cz> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="F2N84YK6LLJXClFdOqgwCIfCyLEVXertE" 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) --F2N84YK6LLJXClFdOqgwCIfCyLEVXertE Content-Type: multipart/mixed; boundary="3Cz2OiUUrvaBOVrB08XAbacoJFG2yQozq"; protected-headers="v1" From: Qu Wenruo To: dsterba@suse.cz, Qu Wenruo , Qu Wenruo , linux-btrfs@vger.kernel.org Message-ID: <63697e20-9c39-da22-437d-b43612f25d3c@suse.de> 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> In-Reply-To: <20181019091516.GB16290@twin.jikos.cz> --3Cz2OiUUrvaBOVrB08XAbacoJFG2yQozq 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=885:15, David Sterba wrote: > On Fri, Oct 19, 2018 at 07:29:26AM +0800, Qu Wenruo wrote: >> >> >> On 2018/10/19 =E4=B8=8A=E5=8D=8812:20, David Sterba wrote: >>> On Thu, Oct 18, 2018 at 07:17:27PM +0800, Qu Wenruo wrote: >>>> +void btrfs_qgroup_clean_swapped_blocks(struct btrfs_root *root) >>>> +{ >>>> + struct btrfs_qgroup_swapped_blocks *swapped_blocks; >>>> + struct btrfs_qgroup_swapped_block *cur, *next; >>>> + int i; >>>> + >>>> + swapped_blocks =3D &root->swapped_blocks; >>>> + >>>> + spin_lock(&swapped_blocks->lock); >>>> + if (!swapped_blocks->swapped) >>>> + goto out; >>>> + for (i =3D 0; i < BTRFS_MAX_LEVEL; i++) { >>>> + struct rb_root *cur_root =3D &swapped_blocks->blocks[i]; >>>> + >>>> + rbtree_postorder_for_each_entry_safe(cur, next, cur_root, >>>> + node) { >>>> + rb_erase(&cur->node, cur_root); >>> >>> https://elixir.bootlin.com/linux/latest/source/include/linux/rbtree.h= #L141 >>> >>> rb_erase must not be used on the same pointer that >>> rbtree_postorder_for_each_entry_safe iterates, here it's cur. >> >> Oh, thanks for pointing this out. >> >> So we must go the old while(rb_first()) loop... >=20 > I just realized the postorder iterator can be used here. The forbidden > pattern is >=20 > rbtree_postorder_for_each_entry_safe() { > rb_erase(); > } 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 and true while(rb_first()) loop. Or did I miss something? Thanks, Qu >=20 > But you also do kfree right after the erase, and the iterator is fine > with that and rb_erase is pointless for an entry that's being freed > anyway. >=20 --3Cz2OiUUrvaBOVrB08XAbacoJFG2yQozq-- --F2N84YK6LLJXClFdOqgwCIfCyLEVXertE Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEELd9y5aWlW6idqkLhwj2R86El/qgFAlvJp/QACgkQwj2R86El /qj/qgf9GfbJXAkg8GZdMMhPpHg0wo8Z2Pz8n/da8f3kNziBMNdN/h/nva8dnli2 Aro3PKmmpKh/FI+KOj+4fViIQqmLVocO8sbYdE2MZ/a41OtkSMd3YPdu/dFU0Z4B kEL3V23Uuk1zFcPCGkWhSPX7tSKOmPqanNbUgamLf37dOElr9oiCVGMkMQMDIpu3 +YGFTGUoYvyVaIXRCge6xkpMAu+0ito7iyl75LQDabuKpMc2ab/cu38SAwUtMYIy +d8iHAtcUk5MmXHdocHodt4SazJkHHP2i7qioXgLVQ4oGk+AE79P0L3SkswFvPea 4hQwNsWDVKT4bX/Tdac/pOEFVj7NfQ== =UoMx -----END PGP SIGNATURE----- --F2N84YK6LLJXClFdOqgwCIfCyLEVXertE--