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 B56BBC433E2 for ; Mon, 15 Jun 2020 16:44:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 903432067B for ; Mon, 15 Jun 2020 16:44:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="efZJDBmW" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731048AbgFOQoS (ORCPT ); Mon, 15 Jun 2020 12:44:18 -0400 Received: from userp2130.oracle.com ([156.151.31.86]:51556 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729966AbgFOQoS (ORCPT ); Mon, 15 Jun 2020 12:44:18 -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 05FGfomx068616; Mon, 15 Jun 2020 16:43:56 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=z9N145QeLFtuW6lOD/XlVVhO41DMyI6eL9hBSNciMQ4=; b=efZJDBmW2wayZ/d6Yf8a0ltjT2xt77XIktp/1x3HeiO+fOMbX8+F4BPhKR85GltR5vWy /gspXvjlarpq9Wfd94Xe4s53ygCYOgKhRCg48owIavnq4L5+qf9MlHeHqL/sl5GfBdLt 1le0QWqqZCGhvKP1kfCyAbVkz4ZRH7cK/yLvARz58yIXVIDW5gcTNE+w1IwnC/IxKG96 UB3C7qRFwATjg1Srhn2p3z3S7D/GVlKilglPzvLshfeVF9sTYg4pYFvvG34X3VTHEOkN 9iYZlT1esZzFFNT7bI3KZwRdAGhEaG1TjNSjz7soeGmawrSQiRUoOZuuz7HvBGFc6M8O Tg== Received: from userp3020.oracle.com (userp3020.oracle.com [156.151.31.79]) by userp2130.oracle.com with ESMTP id 31p6s220e1-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Mon, 15 Jun 2020 16:43:56 +0000 Received: from pps.filterd (userp3020.oracle.com [127.0.0.1]) by userp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 05FGdIuQ039770; Mon, 15 Jun 2020 16:43:56 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by userp3020.oracle.com with ESMTP id 31p6db8ukr-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 15 Jun 2020 16:43:55 +0000 Received: from abhmp0020.oracle.com (abhmp0020.oracle.com [141.146.116.26]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 05FGhrBB031236; Mon, 15 Jun 2020 16:43:53 GMT Received: from localhost (/67.169.218.210) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 15 Jun 2020 09:43:53 -0700 Date: Mon, 15 Jun 2020 09:43:51 -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: <20200615164351.GF11255@magnolia> References: <20200615160830.8471-1-longman@redhat.com> <20200615160830.8471-3-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200615160830.8471-3-longman@redhat.com> X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9653 signatures=668680 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 adultscore=0 suspectscore=1 mlxlogscore=999 mlxscore=0 phishscore=0 bulkscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2006150128 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9653 signatures=668680 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 lowpriorityscore=0 impostorscore=0 clxscore=1011 mlxscore=0 mlxlogscore=999 priorityscore=1501 phishscore=0 malwarescore=0 suspectscore=1 spamscore=0 cotscore=-2147483648 bulkscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2006150128 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 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. Also: Why not set PF_MEMALLOC_NOFS at the start of the freeze call chain? --D > + * So even if fs reclaim > + * is being done, it won't happen to this filesystem. In this case, > + * PF_MEMALLOC_NOLOCKDEP should be set to avoid false positive > + * lockdep splat like: > + * > + * CPU0 CPU1 > + * ---- ---- > + * lock(sb_internal); > + * lock(fs_reclaim); > + * lock(sb_internal); > + * lock(fs_reclaim); > + * > + * *** DEADLOCK *** > + */ > + if (PF_MEMALLOC_NOLOCKDEP && (flags & XFS_TRANS_NO_WRITECOUNT)) > + current_set_flags_nested(&pflags, PF_MEMALLOC_NOLOCKDEP); > > /* > * Allocate the handle before we do our freeze accounting and setting up > @@ -284,13 +304,15 @@ xfs_trans_alloc( > error = xfs_trans_reserve(tp, resp, blocks, rtextents); > if (error) { > xfs_trans_cancel(tp); > - return error; > + goto out; > } > > trace_xfs_trans_alloc(tp, _RET_IP_); > - > *tpp = tp; > - return 0; > +out: > + if (PF_MEMALLOC_NOLOCKDEP && (pflags != -1)) > + current_restore_flags_nested(&pflags, PF_MEMALLOC_NOLOCKDEP); > + return error; > } > > /* > -- > 2.18.1 >