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=-5.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLACK autolearn=no 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 8EE63C433DF for ; Mon, 20 Jul 2020 15:32:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 66CD422482 for ; Mon, 20 Jul 2020 15:32:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="dr+FFtEE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726769AbgGTPcL (ORCPT ); Mon, 20 Jul 2020 11:32:11 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:37969 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726858AbgGTPcL (ORCPT ); Mon, 20 Jul 2020 11:32:11 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1595259129; h=from:from:reply-to: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=WuO0ceoCrlI5WXUN1sWSIg1Q1X5L1heUQCujYy6OI5U=; b=dr+FFtEEHZfOORQeyMRiWp/aHfxgHzNtEgn3UM/mCXO2a6zYQkdVWUW3RtEszHOP1OjVn9 jdn3Mr3/5HeXjAPO8tCjMi+G/couIHL6uyg+KCWx5D5qEll+7JnQcOIIbVSzcmh3oXtrWT tMbu4TSjkcHbr+X75CCgL1GxKADoAmw= 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-102-vnxIcrmOOIilaeTxaZfx1A-1; Mon, 20 Jul 2020 11:32:07 -0400 X-MC-Unique: vnxIcrmOOIilaeTxaZfx1A-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 69853106B247; Mon, 20 Jul 2020 15:32:06 +0000 (UTC) Received: from colo-mx.corp.redhat.com (colo-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.21]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4433C710A4; Mon, 20 Jul 2020 15:32:06 +0000 (UTC) Received: from zmail18.collab.prod.int.phx2.redhat.com (zmail18.collab.prod.int.phx2.redhat.com [10.5.83.21]) by colo-mx.corp.redhat.com (Postfix) with ESMTP id 0DB6D94EE2; Mon, 20 Jul 2020 15:32:06 +0000 (UTC) Date: Mon, 20 Jul 2020 11:32:03 -0400 (EDT) From: Waiman Long Reply-To: Waiman Long To: "Darrick J. Wong" Cc: linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, Dave Chinner , Qian Cai , Eric Sandeen Message-ID: <104087053.24407245.1595259123778.JavaMail.zimbra@redhat.com> In-Reply-To: <20200713164112.GZ7606@magnolia> References: <20200707191629.13911-1-longman@redhat.com> <20200713164112.GZ7606@magnolia> Subject: Re: [PATCH v6] xfs: Fix false positive lockdep warning with sb_internal & fs_reclaim MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [10.10.113.230, 10.4.195.2] Thread-Topic: Fix false positive lockdep warning with sb_internal & fs_reclaim Thread-Index: WmhqTmYfplYkpIlak7AmgyVLRnpP0Q== 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 ----- 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? Thanks, Longman