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=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY 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 AEED4C433E0 for ; Mon, 13 Jul 2020 16:41:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 88A212067D for ; Mon, 13 Jul 2020 16:41:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="xUm8TAgC" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730179AbgGMQlX (ORCPT ); Mon, 13 Jul 2020 12:41:23 -0400 Received: from userp2130.oracle.com ([156.151.31.86]:49514 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729751AbgGMQlW (ORCPT ); Mon, 13 Jul 2020 12:41:22 -0400 Received: from pps.filterd (userp2130.oracle.com [127.0.0.1]) by userp2130.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 06DGM1J5177362; Mon, 13 Jul 2020 16:41:15 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=date : from : to : cc : subject : message-id : references : mime-version : content-type : in-reply-to; s=corp-2020-01-29; bh=OdIBi5hUo2/VqBKmf+cLwz5gWjKz/BgHq+yufd/HaRc=; b=xUm8TAgCkMgEOV9iB5QC8oH+4bIqa5sbM53IYKuzPyH79yZpFXxHVVoAL/45Mcw9p2Pe NN1fRoa3b3+y3C3CgkuUkHi+4cvm9oHTbYFrcTtEQwzq7f4x6aCAr7UJyq0A1MAntc9j 5tHEMdRdpkSDfXarvtNn/BxoXBSGsBICq/ppkvXlLsHpyB1XqA+n7zr3ZDYeMUDTjRvN z0DEpTsvtHgOrwh/zFbXt6aFUwIqkK8vQ8m8oJY1L/bpjzdp7E7NPuoVXRPqmUNGIRzf yqPjnKTCLyHt2EmdJUHcQIBPQmX0nYJd52xwTa3uzbachCZEjWB/VT4GxZrlv0m/qjbl tg== Received: from userp3030.oracle.com (userp3030.oracle.com [156.151.31.80]) by userp2130.oracle.com with ESMTP id 3274ur06s7-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Mon, 13 Jul 2020 16:41:15 +0000 Received: from pps.filterd (userp3030.oracle.com [127.0.0.1]) by userp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 06DGMZu6094523; Mon, 13 Jul 2020 16:41:15 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by userp3030.oracle.com with ESMTP id 327qbvvtg8-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 13 Jul 2020 16:41:14 +0000 Received: from abhmp0006.oracle.com (abhmp0006.oracle.com [141.146.116.12]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 06DGfDmK031181; Mon, 13 Jul 2020 16:41:13 GMT Received: from localhost (/10.159.128.100) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 13 Jul 2020 09:41:13 -0700 Date: Mon, 13 Jul 2020 09:41:12 -0700 From: "Darrick J. Wong" To: Waiman Long Cc: linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, Dave Chinner , Qian Cai , Eric Sandeen Subject: Re: [PATCH v6] xfs: Fix false positive lockdep warning with sb_internal & fs_reclaim Message-ID: <20200713164112.GZ7606@magnolia> References: <20200707191629.13911-1-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200707191629.13911-1-longman@redhat.com> X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9681 signatures=668680 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=1 spamscore=0 mlxlogscore=999 bulkscore=0 malwarescore=0 mlxscore=0 phishscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2007130120 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9681 signatures=668680 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 lowpriorityscore=0 impostorscore=0 suspectscore=1 phishscore=0 spamscore=0 mlxlogscore=999 malwarescore=0 mlxscore=0 priorityscore=1501 adultscore=0 bulkscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2007130120 Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org 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 --D > --- > fs/xfs/xfs_super.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c > index 379cbff438bc..0797a96b83d6 100644 > --- a/fs/xfs/xfs_super.c > +++ b/fs/xfs/xfs_super.c > @@ -913,11 +913,21 @@ xfs_fs_freeze( > struct super_block *sb) > { > struct xfs_mount *mp = XFS_M(sb); > + unsigned int flags; > + int ret; > > + /* > + * The filesystem is now frozen far enough that memory reclaim > + * cannot safely operate on the filesystem. Hence we need to > + * set a GFP_NOFS context here to avoid recursion deadlocks. > + */ > + flags = memalloc_nofs_save(); > xfs_stop_block_reaping(mp); > xfs_save_resvblks(mp); > xfs_quiesce_attr(mp); > - return xfs_sync_sb(mp, true); > + ret = xfs_sync_sb(mp, true); > + memalloc_nofs_restore(flags); > + return ret; > } > > STATIC int > -- > 2.18.1 >