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=-1.0 required=3.0 tests=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 E5EF3C43381 for ; Thu, 21 Feb 2019 14:21:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BBD30206A3 for ; Thu, 21 Feb 2019 14:21:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725891AbfBUOVL (ORCPT ); Thu, 21 Feb 2019 09:21:11 -0500 Received: from mx2.suse.de ([195.135.220.15]:42556 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725820AbfBUOVL (ORCPT ); Thu, 21 Feb 2019 09:21:11 -0500 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 5F18DB183; Thu, 21 Feb 2019 14:21:09 +0000 (UTC) Subject: Re: [bug report] btrfs: locking: Add extra check in btrfs_init_new_buffer() to avoid deadlock To: Dan Carpenter Cc: linux-btrfs@vger.kernel.org References: <20190221141347.GA20330@kadam> From: Qu Wenruo Openpgp: preference=signencrypt Autocrypt: addr=wqu@suse.de; prefer-encrypt=mutual; keydata= mQENBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB AAG0F1F1IFdlbnJ1byA8d3F1QHN1c2UuZGU+iQFUBBMBCAA+AhsDBQsJCAcCBhUICQoLAgQW AgMBAh4BAheAFiEELd9y5aWlW6idqkLhwj2R86El/qgFAlnVgp0FCQlmAm4ACgkQwj2R86El /qilmgf/cUq9kFQo577ku5gc6rFpVg68ublBwjYpwjw0b//xo+Wo1wm+RRbUGs+djSZAqw12 D4F3r0mBTI7abUCNWAbFkYZSAIFVi0DMkjypIVS7PSaEt04rM9VBTToE+YqU6WENeJ57R2p2 +hI0wZrBwxObdsdaOtxWtsp3bmhIbdqxSKrtXuRawy4KnQYcLuGzOce9okdlbAE0W3KHm1gQ oNAe6FX8nC9qo14m8LqEbThYH+qj4iCMlN8HIfbSx4F3e7nHZ+UAMW+E/lnMRkIB9Df+JyVd /NlXzIjZAggcWsqpx6D4wyAuexKWkiGQeUeArUNihAwXjmyqWPGmjVyIh+oC6LkBDQRZ1YGv AQgAqlPrYeBLMv3PAZ75YhQIwH6c4SNcB++hQ9TCT5gIQNw51+SQzkXIGgmzxMIS49cZcE4K Xk/kHw5hieQeQZa60BWVRNXwoRI4ib8okgDuMkD5Kz1WEyO149+BZ7HD4/yK0VFJGuvDJR8T 7RZwB69uVSLjkuNZZmCmDcDzS0c/SJOg5nkxt1iTtgUETb1wNKV6yR9XzRkrEW/qShChyrS9 fNN8e9c0MQsC4fsyz9Ylx1TOY/IF/c6rqYoEEfwnpdlz0uOM1nA1vK+wdKtXluCa79MdfaeD /dt76Kp/o6CAKLLcjU1Iwnkq1HSrYfY3HZWpvV9g84gPwxwxX0uXquHxLwARAQABiQE8BBgB CAAmFiEELd9y5aWlW6idqkLhwj2R86El/qgFAlnVga8CGwwFCQPCZwAACgkQwj2R86El/qgN 8Qf+M0vM2Idwm5txZZSs+/kSgcPxEwYmxUinnUJGyc0ZWYQXPl0cBetZon9El0naijGzNWvf HxIPB+ZFehk6Otgc78p1a3/xck/s1myFRLrmbbTJNoFiyL25ljcq0J8z5Zp4yuABL2RiLdaZ Pt/jfwjBHwGR+QKp6dD2qMrUWf9b7TFzYDMZXzZ2/eoIgtyjEelNBPrIgOFe24iKMjaGjd97 fJuRcBMHdhUAxvXQF1oRtd83JvYJ5OtwTd8MgkEfl+fo7HwWkuHbzc70L4fFKv2BowqFdaHy mId1ijGPGr46tuZ5a4cw/zbaPYx6fJ4sK9tSv/6V1QPNUdqml6hm6pfs6A== Message-ID: Date: Thu, 21 Feb 2019 22:21:03 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <20190221141347.GA20330@kadam> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="1GkfEK7Wx4qB9n2LAKCUdQWD376fPIf0B" 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) --1GkfEK7Wx4qB9n2LAKCUdQWD376fPIf0B Content-Type: multipart/mixed; boundary="OXKofnd9cBXyiE4L5BPSU9UJtwOG0PnbI"; protected-headers="v1" From: Qu Wenruo To: Dan Carpenter Cc: linux-btrfs@vger.kernel.org Message-ID: Subject: Re: [bug report] btrfs: locking: Add extra check in btrfs_init_new_buffer() to avoid deadlock References: <20190221141347.GA20330@kadam> In-Reply-To: <20190221141347.GA20330@kadam> --OXKofnd9cBXyiE4L5BPSU9UJtwOG0PnbI Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 2019/2/21 =E4=B8=8B=E5=8D=8810:13, Dan Carpenter wrote: > [ This one is not actually your fault. It's the core code which is > confusing. -dan ] >=20 > Hello Qu Wenruo, >=20 > The patch b72c3aba09a5: "btrfs: locking: Add extra check in > btrfs_init_new_buffer() to avoid deadlock" from Aug 21, 2018, leads > to the following static checker warning: >=20 > fs/btrfs/extent-tree.c:8556 btrfs_init_new_buffer() > warn: possible NULL dereference of 'buf' >=20 > fs/btrfs/extent-tree.c > 8540 static struct extent_buffer * > 8541 btrfs_init_new_buffer(struct btrfs_trans_handle *trans, struct= btrfs_root *root, > 8542 u64 bytenr, int level, u64 owner) > 8543 { > 8544 struct btrfs_fs_info *fs_info =3D root->fs_info; > 8545 struct extent_buffer *buf; > 8546=20 > 8547 buf =3D btrfs_find_create_tree_block(fs_info, bytenr); >=20 > The btrfs_find_create_tree_block() function either returns > alloc_test_extent_buffer() which returns NULL on error You caught me! Indeed that's a possible NULL return case. The only good news is it shouldn't affect release build which normally doesn't enabled CONFIG_BTRFS_FS_RUN_SANITY_TESTS. I'll fix it by unifying the return pointer. Thanks for pointing this out, Qu > or > alloc_extent_buffer() which returns error pointers on error. It > confuses static checkers and me also. >=20 > 8548 if (IS_ERR(buf)) > 8549 return buf; > 8550=20 > 8551 /* > 8552 * Extra safety check in case the extent tree is corrupted an= d extent > 8553 * allocator chooses to use a tree block which is already use= d and > 8554 * locked. > 8555 */ > --> 8556 if (buf->lock_owner =3D=3D current->pid) { > 8557 btrfs_err_rl(fs_info, > 8558 "tree block %llu owner %llu already locked by pid=3D%d, extent= tree corruption detected", > 8559 buf->start, btrfs_header_owner(buf), current->pid); > 8560 free_extent_buffer(buf); >=20 > regards, > dan carpenter >=20 --OXKofnd9cBXyiE4L5BPSU9UJtwOG0PnbI-- --1GkfEK7Wx4qB9n2LAKCUdQWD376fPIf0B Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEELd9y5aWlW6idqkLhwj2R86El/qgFAlxus88ACgkQwj2R86El /qjC0Qf+IuS1/sZ/HXBbyTmTsA5jjd+aYGz2q/r7vF1kNkA/CBzR4Rv7ivDeB23S i1ZOtjZn6wHnYHFgbQhMdjJkXu2moVWaV6t2kqTla29OAX1oCwslj3P6izg9doXz nU7dVSN9jNHlp99vgV8nkAR9Hog4FMEU2HDb6qOLV/JyyGTxgvUrNYe11+dlRrq1 kmpofuURydlQLr9zLtT1uEJm7MTC+d8J3BiGdwSWva628/nCs3luJVIwHLyLiwn/ Xb6ZwGx7XQRxvmJN+wuwIlIdUJ1yqdIUGTUxwmzjg/8GwQl9Ino+WHLjuZsvRsdy wv6MBeDOboS8ERRmFI/KwGs+Vva3CA== =GWLm -----END PGP SIGNATURE----- --1GkfEK7Wx4qB9n2LAKCUdQWD376fPIf0B--