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=-8.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 214F9C433E6 for ; Mon, 20 Jul 2020 16:39:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 013B422BF3 for ; Mon, 20 Jul 2020 16:39:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="K64e+By0" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729391AbgGTPtD (ORCPT ); Mon, 20 Jul 2020 11:49:03 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:42125 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730720AbgGTPrC (ORCPT ); Mon, 20 Jul 2020 11:47:02 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1595260021; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=hQ1H7l9Ohk9cYexEWkkOl7WIuCDqSZlPZluQHWvxb1I=; b=K64e+By0Ok8vfbRotOtKcGeXuftLqivKDiQUBzmuerU+WRhbOB2q2GyqT5m1rf4/ATEs4z jtoVh2uO5GOIzeI3InnWBZ7AHrVtPAou9cGeXhzdsnrd0LgauUd2GBl3s5QxcQCQFtyCsA nCe+yUwUWJilcsa/v44+EE5ZiBcBa7w= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-66-kQ0JMy5zMwax-kYED5mPiQ-1; Mon, 20 Jul 2020 11:46:59 -0400 X-MC-Unique: kQ0JMy5zMwax-kYED5mPiQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1DC0818A1DFE; Mon, 20 Jul 2020 15:46:58 +0000 (UTC) Received: from llong.remote.csb (ovpn-113-230.rdu2.redhat.com [10.10.113.230]) by smtp.corp.redhat.com (Postfix) with ESMTP id 46C8C7EF81; Mon, 20 Jul 2020 15:46:57 +0000 (UTC) Subject: Re: [PATCH v6] xfs: Fix false positive lockdep warning with sb_internal & fs_reclaim To: "Darrick J. Wong" Cc: linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, Dave Chinner , Qian Cai , Eric Sandeen References: <20200707191629.13911-1-longman@redhat.com> <20200713164112.GZ7606@magnolia> <104087053.24407245.1595259123778.JavaMail.zimbra@redhat.com> <20200720154043.GV7625@magnolia> From: Waiman Long Organization: Red Hat Message-ID: Date: Mon, 20 Jul 2020 11:46:56 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200720154043.GV7625@magnolia> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On 7/20/20 11:40 AM, Darrick J. Wong wrote: > On Mon, Jul 20, 2020 at 11:32:03AM -0400, Waiman Long wrote: >> >> ----- Original Message ----- >> From: "Darrick J. Wong" >> To: "Waiman Long" >> Cc: linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, "Dave Chinner" , "Qian Cai" , "Eric Sandeen" >> Sent: Monday, July 13, 2020 12:41:12 PM >> Subject: Re: [PATCH v6] xfs: Fix false positive lockdep warning with sb_internal & fs_reclaim >> >> On Tue, Jul 07, 2020 at 03:16:29PM -0400, Waiman Long wrote: >>> Depending on the workloads, the following circular locking dependency >>> warning between sb_internal (a percpu rwsem) and fs_reclaim (a pseudo >>> lock) may show up: >>> >>> ====================================================== >>> WARNING: possible circular locking dependency detected >>> 5.0.0-rc1+ #60 Tainted: G W >>> ------------------------------------------------------ >>> fsfreeze/4346 is trying to acquire lock: >>> 0000000026f1d784 (fs_reclaim){+.+.}, at: >>> fs_reclaim_acquire.part.19+0x5/0x30 >>> >>> but task is already holding lock: >>> 0000000072bfc54b (sb_internal){++++}, at: percpu_down_write+0xb4/0x650 >>> >>> which lock already depends on the new lock. >>> : >>> Possible unsafe locking scenario: >>> >>> CPU0 CPU1 >>> ---- ---- >>> lock(sb_internal); >>> lock(fs_reclaim); >>> lock(sb_internal); >>> lock(fs_reclaim); >>> >>> *** DEADLOCK *** >>> >>> 4 locks held by fsfreeze/4346: >>> #0: 00000000b478ef56 (sb_writers#8){++++}, at: percpu_down_write+0xb4/0x650 >>> #1: 000000001ec487a9 (&type->s_umount_key#28){++++}, at: freeze_super+0xda/0x290 >>> #2: 000000003edbd5a0 (sb_pagefaults){++++}, at: percpu_down_write+0xb4/0x650 >>> #3: 0000000072bfc54b (sb_internal){++++}, at: percpu_down_write+0xb4/0x650 >>> >>> stack backtrace: >>> Call Trace: >>> dump_stack+0xe0/0x19a >>> print_circular_bug.isra.10.cold.34+0x2f4/0x435 >>> check_prev_add.constprop.19+0xca1/0x15f0 >>> validate_chain.isra.14+0x11af/0x3b50 >>> __lock_acquire+0x728/0x1200 >>> lock_acquire+0x269/0x5a0 >>> fs_reclaim_acquire.part.19+0x29/0x30 >>> fs_reclaim_acquire+0x19/0x20 >>> kmem_cache_alloc+0x3e/0x3f0 >>> kmem_zone_alloc+0x79/0x150 >>> xfs_trans_alloc+0xfa/0x9d0 >>> xfs_sync_sb+0x86/0x170 >>> xfs_log_sbcount+0x10f/0x140 >>> xfs_quiesce_attr+0x134/0x270 >>> xfs_fs_freeze+0x4a/0x70 >>> freeze_super+0x1af/0x290 >>> do_vfs_ioctl+0xedc/0x16c0 >>> ksys_ioctl+0x41/0x80 >>> __x64_sys_ioctl+0x73/0xa9 >>> do_syscall_64+0x18f/0xd23 >>> entry_SYSCALL_64_after_hwframe+0x49/0xbe >>> >>> This is a false positive as all the dirty pages are flushed out before >>> the filesystem can be frozen. >>> >>> One way to avoid this splat is to add GFP_NOFS to the affected allocation >>> calls by using the memalloc_nofs_save()/memalloc_nofs_restore() pair. >>> This shouldn't matter unless the system is really running out of memory. >>> In that particular case, the filesystem freeze operation may fail while >>> it was succeeding previously. >>> >>> Without this patch, the command sequence below will show that the lock >>> dependency chain sb_internal -> fs_reclaim exists. >>> >>> # fsfreeze -f /home >>> # fsfreeze --unfreeze /home >>> # grep -i fs_reclaim -C 3 /proc/lockdep_chains | grep -C 5 sb_internal >>> >>> After applying the patch, such sb_internal -> fs_reclaim lock dependency >>> chain can no longer be found. Because of that, the locking dependency >>> warning will not be shown. >>> >>> Suggested-by: Dave Chinner >>> Signed-off-by: Waiman Long >> Looks good to me, >> Reviewed-by: Darrick J. Wong >> >> Will this patch be merged into the xfs tree soon? > It should appear in for-next in the next day or so. I am trying to push > there only every other couple of weeks to reduce the amount of developer > tree rebasing that has to go on when people are trying to land a complex > series. > > --D Thanks for the clarification. Cheers, Longman