From nobody Thu Sep 18 06:56:52 2025 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 25266C4332F for ; Thu, 8 Dec 2022 14:07:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229717AbiLHOHW (ORCPT ); Thu, 8 Dec 2022 09:07:22 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42248 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229602AbiLHOHQ (ORCPT ); Thu, 8 Dec 2022 09:07:16 -0500 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D34B3F018 for ; Thu, 8 Dec 2022 06:07:14 -0800 (PST) Received: from kwepemm600013.china.huawei.com (unknown [172.30.72.54]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4NSbV36Xm6zJpCN; Thu, 8 Dec 2022 22:03:39 +0800 (CST) Received: from huawei.com (10.175.127.227) by kwepemm600013.china.huawei.com (7.193.23.68) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Thu, 8 Dec 2022 22:07:11 +0800 From: Zhihao Cheng To: , , , , CC: , , , Subject: [dm-devel][PATCH -next] dm thin: Use last transaction's pmd->root when commit failed Date: Thu, 8 Dec 2022 22:28:02 +0800 Message-ID: <20221208142802.1479048-1-chengzhihao1@huawei.com> X-Mailer: git-send-email 2.31.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Originating-IP: [10.175.127.227] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To kwepemm600013.china.huawei.com (7.193.23.68) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Recently we found a softlock up problem in dm thin pool looking up btree caused by corrupted metadata: Kernel panic - not syncing: softlockup: hung tasks CPU: 7 PID: 2669225 Comm: kworker/u16:3 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996) Workqueue: dm-thin do_worker [dm_thin_pool] Call Trace: dump_stack+0x9c/0xd3 panic+0x35d/0x6b9 watchdog_timer_fn.cold+0x16/0x25 __run_hrtimer+0xa2/0x2d0 RIP: 0010:__relink_lru+0x102/0x220 [dm_bufio] __bufio_new+0x11f/0x4f0 [dm_bufio] new_read+0xa3/0x1e0 [dm_bufio] dm_bm_read_lock+0x33/0xd0 [dm_persistent_data] ro_step+0x63/0x100 [dm_persistent_data] btree_lookup_raw.constprop.0+0x44/0x220 [dm_persistent_data] dm_btree_lookup+0x16f/0x210 [dm_persistent_data] dm_thin_find_block+0x12c/0x210 [dm_thin_pool] __process_bio_read_only+0xc5/0x400 [dm_thin_pool] process_thin_deferred_bios+0x1a4/0x4a0 [dm_thin_pool] process_one_work+0x3c5/0x730 Following process may generate a broken btree mixed with fresh and stale nodes, which could let dm thin trapped into an infinite loop while looking up data block: Transaction 1: pmd->root =3D A, A->B->C // One path in btree pmd->root =3D X, X->Y->Z // Copy-up Transaction 2: X,Z is updated on disk, Y is written failed. // Commit failed, dm thin becomes read-only. process_bio_read_only dm_thin_find_block __find_block dm_btree_lookup(pmd->root) The pmd->root points to a broken btree, Y may contain stale node pointing to any block, for example X, which lets dm thin trapped into a dead loop while looking up Z. Fix it by setting pmd->root in __open_metadata(), so that dm thin will use last transaction's pmd->root if commit failed. Fetch a reproducer in [Link]. Linke: https://bugzilla.kernel.org/show_bug.cgi?id=3D216790 Fixes: 991d9fa02da0 ("dm: add thin provisioning target") Signed-off-by: Zhihao Cheng --- drivers/md/dm-thin-metadata.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/md/dm-thin-metadata.c b/drivers/md/dm-thin-metadata.c index 1a62226ac34e..26c42ee183ed 100644 --- a/drivers/md/dm-thin-metadata.c +++ b/drivers/md/dm-thin-metadata.c @@ -724,6 +724,15 @@ static int __open_metadata(struct dm_pool_metadata *pm= d) goto bad_cleanup_data_sm; } =20 + /* + * For pool metadata opening process, root setting is redundant + * because it will be set again in __begin_transaction(). But dm + * pool aborting process really needs to get last transaction's + * root in case accessing broken btree. + */ + pmd->root =3D le64_to_cpu(disk_super->data_mapping_root); + pmd->details_root =3D le64_to_cpu(disk_super->device_details_root); + __setup_btree_details(pmd); dm_bm_unlock(sblock); =20 --=20 2.31.1