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=-6.8 required=3.0 tests=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 C196FC433E1 for ; Tue, 16 Jun 2020 16:32:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A39E2208B3 for ; Tue, 16 Jun 2020 16:32:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="w2JF/HtV" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730510AbgFPQcP (ORCPT ); Tue, 16 Jun 2020 12:32:15 -0400 Received: from aserp2120.oracle.com ([141.146.126.78]:51346 "EHLO aserp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729167AbgFPQcO (ORCPT ); Tue, 16 Jun 2020 12:32:14 -0400 Received: from pps.filterd (aserp2120.oracle.com [127.0.0.1]) by aserp2120.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 05GGRggB090207; Tue, 16 Jun 2020 16:32:00 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=iGPIvJn8jlhE50vAJGlUGCgtoy3/I45W7Z0/PlOasX0=; b=w2JF/HtVXhLwfJQ3TTg+ggbNkS8gFMJDDIvvcQYifD7udfPJy3JQa5+DwjE3bB9jIEU3 qftzeZKhTHVNSFvJ95n5rxqbE8kFLvxFqvDzLdeu4Q7zXpReG/KNOgKtiSC7MjRbSz2Q Gi0m5k5AK5NJppR35UPEcHA0NrWc+B+Oa1Gd+KaH3aCMDR9xG1D4cdU8lbf0zmzDi4GW kF1bOBVjpE1FiGQoPoKhvkZQMCSCxndfTgUtX2RoAjSjMD14mbnhxp3tkfKyYF8uTl4a zl5ReyJBQi+jkGGqP3xA9SdID27nOyuJAr8TxWu36paOaoUPFFHICZliXpGGn/htagoa fQ== Received: from aserp3020.oracle.com (aserp3020.oracle.com [141.146.126.70]) by aserp2120.oracle.com with ESMTP id 31p6e7yv80-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Tue, 16 Jun 2020 16:32:00 +0000 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 05GGT38t144679; Tue, 16 Jun 2020 16:30:00 GMT Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by aserp3020.oracle.com with ESMTP id 31p6dh2n50-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 16 Jun 2020 16:30:00 +0000 Received: from abhmp0013.oracle.com (abhmp0013.oracle.com [141.146.116.19]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 05GGTwKo016199; Tue, 16 Jun 2020 16:29:58 GMT Received: from localhost (/67.169.218.210) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 16 Jun 2020 09:29:58 -0700 Date: Tue, 16 Jun 2020 09:29:57 -0700 From: "Darrick J. Wong" To: Waiman Long Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, Dave Chinner , Qian Cai , Eric Sandeen , Andrew Morton Subject: Re: [PATCH 2/2] xfs: Fix false positive lockdep warning with sb_internal & fs_reclaim Message-ID: <20200616162957.GO11245@magnolia> References: <20200615160830.8471-1-longman@redhat.com> <20200615160830.8471-3-longman@redhat.com> <20200615164351.GF11255@magnolia> <2f03b074-4732-01e4-b0ff-482bb4bb44ce@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2f03b074-4732-01e4-b0ff-482bb4bb44ce@redhat.com> X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9654 signatures=668680 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=5 adultscore=0 bulkscore=0 phishscore=0 malwarescore=0 spamscore=0 mlxlogscore=999 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2006160117 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9654 signatures=668680 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 spamscore=0 impostorscore=0 bulkscore=0 clxscore=1015 malwarescore=0 suspectscore=5 mlxscore=0 phishscore=0 mlxlogscore=999 lowpriorityscore=0 cotscore=-2147483648 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2006160117 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 15, 2020 at 04:53:38PM -0400, Waiman Long wrote: > On 6/15/20 12:43 PM, Darrick J. Wong wrote: > > On Mon, Jun 15, 2020 at 12:08:30PM -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. > > > > > > Perhaps breaking the fs_reclaim pseudo lock into a per filesystem lock > > > may fix the issue. However, that will greatly complicate the logic and > > > may not be worth it. > > > > > > Another way to fix it is to disable the taking of the fs_reclaim > > > pseudo lock when in the freezing code path as a reclaim on the > > > freezed filesystem is not possible. By using the newly introduced > > > PF_MEMALLOC_NOLOCKDEP flag, lockdep checking is disabled in > > > xfs_trans_alloc() if XFS_TRANS_NO_WRITECOUNT flag is set. > > > > > > In the freezing path, there is another path where memory allocation > > > is being done without the XFS_TRANS_NO_WRITECOUNT flag: > > > > > > xfs_fs_freeze() > > > => xfs_quiesce_attr() > > > => xfs_log_quiesce() > > > => xfs_log_unmount_write() > > > => xlog_unmount_write() > > > => xfs_log_reserve() > > > => xlog_ticket_alloc() > > > > > > In this case, we just disable fs reclaim for this particular 600 bytes > > > memory allocation. > > > > > > 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 > > > --- > > > fs/xfs/xfs_log.c | 9 +++++++++ > > > fs/xfs/xfs_trans.c | 30 ++++++++++++++++++++++++++---- > > > 2 files changed, 35 insertions(+), 4 deletions(-) > > > > > > diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c > > > index 00fda2e8e738..33244680d0d4 100644 > > > --- a/fs/xfs/xfs_log.c > > > +++ b/fs/xfs/xfs_log.c > > > @@ -830,8 +830,17 @@ xlog_unmount_write( > > > xfs_lsn_t lsn; > > > uint flags = XLOG_UNMOUNT_TRANS; > > > int error; > > > + unsigned long pflags; > > > + /* > > > + * xfs_log_reserve() allocates memory. This can lead to fs reclaim > > > + * which may conflicts with the unmount process. To avoid that, > > > + * disable fs reclaim for this allocation. > > > + */ > > > + current_set_flags_nested(&pflags, PF_MEMALLOC_NOFS); > > > error = xfs_log_reserve(mp, 600, 1, &tic, XFS_LOG, 0); > > > + current_restore_flags_nested(&pflags, PF_MEMALLOC_NOFS); > > > + > > > if (error) > > > goto out_err; > > > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c > > > index 3c94e5ff4316..ddb10ad3f51f 100644 > > > --- a/fs/xfs/xfs_trans.c > > > +++ b/fs/xfs/xfs_trans.c > > > @@ -255,7 +255,27 @@ xfs_trans_alloc( > > > struct xfs_trans **tpp) > > > { > > > struct xfs_trans *tp; > > > - int error; > > > + int error = 0; > > > + unsigned long pflags = -1; > > > + > > > + /* > > > + * When XFS_TRANS_NO_WRITECOUNT is set, it means there are no dirty > > > + * data pages in the filesystem at this point. > > That's not true. Look at the other callers of xfs_trans_alloc_empty. > Yes, I am aware of that. I can change it to check the freeze state. > > Also: Why not set PF_MEMALLOC_NOFS at the start of the freeze call > > chain? > > I guess we can do that, but it eliminates a potential source for memory > reclaim leading to freeze error when not much free memory is left. We can go > this route if you think this is not a problem. It sounds like you & Dave had already worked that out, so we can leave this as it is. I saw the untrue claim in the code comment and started asking more questions. ;) (Says me who has been checked out the last few days, not following the various lockdep shuttup patch threads...) --D > Cheers, > Longman >