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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 951B8EB64D9 for ; Thu, 29 Jun 2023 11:55:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231140AbjF2LzR (ORCPT ); Thu, 29 Jun 2023 07:55:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46286 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229987AbjF2LzQ (ORCPT ); Thu, 29 Jun 2023 07:55:16 -0400 Received: from dggsgout11.his.huawei.com (unknown [45.249.212.51]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 31B7F13D for ; Thu, 29 Jun 2023 04:55:15 -0700 (PDT) Received: from mail02.huawei.com (unknown [172.30.67.143]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTP id 4QsH265YNzz4f3prv for ; Thu, 29 Jun 2023 19:55:10 +0800 (CST) Received: from [10.174.177.210] (unknown [10.174.177.210]) by APP2 (Coremail) with SMTP id Syh0CgBnW+kecZ1kgZrlMg--.16719S3; Thu, 29 Jun 2023 19:55:11 +0800 (CST) Message-ID: <4d6ee3b3-6d4b-ddb6-eb8e-e04a7e0c1ab0@huaweicloud.com> Date: Thu, 29 Jun 2023 19:55:10 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 Subject: Re: [PATCH] xfs: fix deadlock when set label online To: Dave Chinner Cc: djwong@kernel.org, dchinner@redhat.com, sandeen@redhat.com, linux-xfs@vger.kernel.org, yangerkun@huawei.com, yukuai3@huawei.com References: <20230626131542.3711391-1-yangerkun@huaweicloud.com> From: yangerkun In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-CM-TRANSID: Syh0CgBnW+kecZ1kgZrlMg--.16719S3 X-Coremail-Antispam: 1UD129KBjvJXoWxCFy8Zr4UWryftr1UCF1UGFg_yoWrJw1xpr ZYkFZ8GrsxKr4F9rs2yw1jq3WrKa1UJa1kXrn0grsYvas8Zr1SgFySqr4agF9rZrs7Cw4j vF10v3s7Xw13Ca7anT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUyEb4IE77IF4wAFF20E14v26r4j6ryUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_tr0E3s1l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Gr1j6F4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x 0267AKxVW0oVCq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG 6I80ewAv7VC0I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFV Cjc4AY6r1j6r4UM4x0Y48IcVAKI48JMxk0xIA0c2IEe2xFo4CEbIxvr21l42xK82IYc2Ij 64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxVAqx4xG67AKxVWUJVWUGwC20s026x 8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r126r1DMIIYrxkI7VAKI48JMIIF0xvE 2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6xkF7I0E14v26r1j6r4UMIIF0xvE42 xK8VAvwI8IcIk0rVWrZr1j6s0DMIIF0xvEx4A2jsIE14v26r1j6r4UMIIF0xvEx4A2jsIE c7CjxVAFwI0_Jr0_GrUvcSsGvfC2KfnxnUUI43ZEXa7IU1zuWJUUUUU== X-CM-SenderInfo: 51dqwvhunx0q5kxd4v5lfo033gof0z/ X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org 在 2023/6/29 7:10, Dave Chinner 写道: > On Tue, Jun 27, 2023 at 04:42:41PM +0800, yangerkun wrote: >> >> >> 在 2023/6/27 5:45, Dave Chinner 写道: >>> On Mon, Jun 26, 2023 at 09:15:42PM +0800, yangerkun wrote: >>>> From: yangerkun >>>> >>>> Combine use of xfs_trans_hold and xfs_trans_set_sync in xfs_sync_sb_buf >>>> can trigger a deadlock once shutdown happened concurrently. xlog_ioend_work >>>> will first unpin the sb(which stuck with xfs_buf_lock), then wakeup >>>> xfs_sync_sb_buf. However, xfs_sync_sb_buf never get the chance to unlock >>>> sb until been wakeup by xlog_ioend_work. >>>> >>>> xfs_sync_sb_buf >>>> xfs_trans_getsb // lock sb buf >>>> xfs_trans_bhold // sb buf keep lock until success commit >>>> xfs_trans_commit >>>> ... >>>> xfs_log_force_seq >>>> xlog_force_lsn >>>> xlog_wait_on_iclog >>>> xlog_wait(&iclog->ic_force_wait... // shutdown happened >>>> xfs_buf_relse // unlock sb buf >>>> >>>> xlog_ioend_work >>>> xlog_force_shutdown >>>> xlog_state_shutdown_callbacks >>>> xlog_cil_process_committed >>>> xlog_cil_committed >>>> ... >>>> xfs_buf_item_unpin >>>> xfs_buf_lock // deadlock >>>> wake_up_all(&iclog->ic_force_wait) >>>> >>>> xfs_ioc_setlabel use xfs_sync_sb_buf to make sure userspace will see the >>>> change for sb immediately. We can simply call xfs_ail_push_all_sync to >>>> do this and sametime fix the deadlock. >>> >>> Why is this deadlock specific to the superblock buffer? >> >> Hi Dave, >> >> Thanks a lot for your revirew! We find this problem when do some code >> reading(which can help us to fix another growfs bug). And then reproduce it >> easily when we set label online frequently with IO error inject at the >> sametime. > > Right, I know how it can be triggered; that's not actually my > concern... > >>> Can't any buffer that is held locked over a synchronous transaction >>> commit deadlock during a shutdown like this? >> >> After check all place use xfs_buf_bhold, it seems xfs_sync_sb_buf is the >> only convict that combine use xfs_trans_hold and xfs_trans_set_sync(I'm not >> familiar with xfs yet, so I may have some problems with my code check)... > > Yes, I can also see that. But my concern is that this change only > addresses the symptom, but leaves the underlying deadlock unsolved. > > Indeed, this isn't xfs_trans_commit() I'm worried about here; it's > the call to xfs_log_force(mp, XFS_LOG_SYNC) or > xfs_log_force_seq(XFS_LOG_SYNC) with a buffer held locked that I'm > worried about. > > i.e. We have a buffer in the CIL (from a previous transaction) that > we currently hold locked while we call xfs_log_force(XFS_LOG_SYNC). > If a shutdown occurs while we are waiting for journal IO completion > to occur, then xlog_ioend_work() will attempt to lock the buffer and > deadlock, right? > > e.g. I'm thinking of things like busy extent flushing (hold AGF + > AGFL + AG btree blocks locked when we call xfs_log_force()) could > also be vulnerable to the same deadlock... You mean something like xfs_allocbt_alloc_block(call xfs_log_force to flush busy extent which keep agf locked sametime)? We call xfs_log_force(mp, XFS_LOG_SYNC) after lock agf and before xfs_trans_commit. It seems ok since xfs_buf_item_unpin will not call xfs_buf_lock because bli_refcount still keep active(once we hold locked agf, the bli_refcount will inc in _xfs_trans_bjoin, and keep it until xfs_trans_commit success(clean agf item) or .iop_unpin(dirty agf item, call from xlog_ioend_work) which can be called after xfs_trans_commit too)... > > If that's true, how do we avoid the shutdown from causing a deadlock > in these situations? > > Cheers, > > Dave.