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=-8.4 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, USER_AGENT_SANE_1 autolearn=ham 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 BC1F3C1975A for ; Wed, 25 Mar 2020 06:06:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 868AC206F8 for ; Wed, 25 Mar 2020 06:06:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="naUh5m58" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726043AbgCYGGd (ORCPT ); Wed, 25 Mar 2020 02:06:33 -0400 Received: from userp2130.oracle.com ([156.151.31.86]:46034 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725911AbgCYGGc (ORCPT ); Wed, 25 Mar 2020 02:06:32 -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 02P5xBx9069156; Wed, 25 Mar 2020 06:06:30 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=x6oBbHEs8ZDdj3KMZYW8ZUgVoKqghQ2fzqluR7qLV6s=; b=naUh5m58EEevwo3rfxQ2QdwjkVr/hUYtpqCnbspKknYiSWJtvC93GnmbcbWww+xkOVA4 GVpd2/Pb+/WmG4EpymUzpnWopsdfEnys3OWAyNkQNUelkZ8F7hpv1VKv6v/Curh+LV2Q lvLw1j3cLjdHj93brK8ELnWV5Us3XmdKeUYdTCJIKNvEsypeMmZIa7K3WfNzkPdYHFOq DnJmmc3X6ISoi/Yc8zWsJAlrhxVDIMRVa90ml/eOOfxvgmRuHWbMYPZdsacf1JEuFHB8 Gey2kXegzJpWb0RqzTQeeqdmsjOxVRd0W2eVC2tVS85lQHkCeUBmqNJYcLIrEK7F8bcW 9g== Received: from aserp3030.oracle.com (aserp3030.oracle.com [141.146.126.71]) by userp2130.oracle.com with ESMTP id 2ywabr7y1j-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 25 Mar 2020 06:06:30 +0000 Received: from pps.filterd (aserp3030.oracle.com [127.0.0.1]) by aserp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 02P5vn9e176338; Wed, 25 Mar 2020 06:06:29 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by aserp3030.oracle.com with ESMTP id 2yxw940u6d-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 25 Mar 2020 06:06:29 +0000 Received: from abhmp0014.oracle.com (abhmp0014.oracle.com [141.146.116.20]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 02P66SBt010867; Wed, 25 Mar 2020 06:06:28 GMT Received: from localhost (/67.169.218.210) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 24 Mar 2020 23:06:27 -0700 Date: Tue, 24 Mar 2020 23:06:27 -0700 From: "Darrick J. Wong" To: linux-xfs@vger.kernel.org Cc: Dave Chinner Subject: [PATCH v2 1/4] xfs: prohibit fs freezing when using empty transactions Message-ID: <20200325060627.GW29339@magnolia> References: <158510667039.922633.6138311243444001882.stgit@magnolia> <158510667670.922633.9371387481128286027.stgit@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <158510667670.922633.9371387481128286027.stgit@magnolia> User-Agent: Mutt/1.9.4 (2018-02-28) X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9570 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 spamscore=0 bulkscore=0 adultscore=0 mlxscore=0 malwarescore=0 mlxlogscore=999 suspectscore=1 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2003250048 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9570 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 suspectscore=1 lowpriorityscore=0 malwarescore=0 phishscore=0 priorityscore=1501 clxscore=1015 adultscore=0 mlxscore=0 mlxlogscore=999 bulkscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2003250048 Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org From: Darrick J. Wong I noticed that fsfreeze can take a very long time to freeze an XFS if there happens to be a GETFSMAP caller running in the background. I also happened to notice the following in dmesg: ------------[ cut here ]------------ WARNING: CPU: 2 PID: 43492 at fs/xfs/xfs_super.c:853 xfs_quiesce_attr+0x83/0x90 [xfs] Modules linked in: xfs libcrc32c ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 ip_set_hash_ip ip_set_hash_net xt_tcpudp xt_set ip_set_hash_mac ip_set nfnetlink ip6table_filter ip6_tables bfq iptable_filter sch_fq_codel ip_tables x_tables nfsv4 af_packet [last unloaded: xfs] CPU: 2 PID: 43492 Comm: xfs_io Not tainted 5.6.0-rc4-djw #rc4 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.10.2-1ubuntu1 04/01/2014 RIP: 0010:xfs_quiesce_attr+0x83/0x90 [xfs] Code: 7c 07 00 00 85 c0 75 22 48 89 df 5b e9 96 c1 00 00 48 c7 c6 b0 2d 38 a0 48 89 df e8 57 64 ff ff 8b 83 7c 07 00 00 85 c0 74 de <0f> 0b 48 89 df 5b e9 72 c1 00 00 66 90 0f 1f 44 00 00 41 55 41 54 RSP: 0018:ffffc900030f3e28 EFLAGS: 00010202 RAX: 0000000000000001 RBX: ffff88802ac54000 RCX: 0000000000000000 RDX: 0000000000000000 RSI: ffffffff81e4a6f0 RDI: 00000000ffffffff RBP: ffff88807859f070 R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000010 R12: 0000000000000000 R13: ffff88807859f388 R14: ffff88807859f4b8 R15: ffff88807859f5e8 FS: 00007fad1c6c0fc0(0000) GS:ffff88807e000000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f0c7d237000 CR3: 0000000077f01003 CR4: 00000000001606a0 Call Trace: xfs_fs_freeze+0x25/0x40 [xfs] freeze_super+0xc8/0x180 do_vfs_ioctl+0x70b/0x750 ? __fget_files+0x135/0x210 ksys_ioctl+0x3a/0xb0 __x64_sys_ioctl+0x16/0x20 do_syscall_64+0x50/0x1a0 entry_SYSCALL_64_after_hwframe+0x49/0xbe These two things appear to be related. The assertion trips when another thread initiates a fsmap request (which uses an empty transaction) after the freezer waited for m_active_trans to hit zero but before the the freezer executes the WARN_ON just prior to calling xfs_log_quiesce. The lengthy delays in freezing happen because the freezer calls xfs_wait_buftarg to clean out the buffer lru list. Meanwhile, the GETFSMAP caller is continuing to grab and release buffers, which means that it can take a very long time for the buffer lru list to empty out. We fix both of these races by calling sb_start_write to obtain freeze protection while using empty transactions for GETFSMAP and for metadata scrubbing. The other two users occur during mount, during which time we cannot fs freeze. Signed-off-by: Darrick J. Wong --- v2: improve comments --- fs/xfs/scrub/scrub.c | 9 +++++++++ fs/xfs/xfs_fsmap.c | 9 +++++++++ fs/xfs/xfs_trans.c | 5 +++++ 3 files changed, 23 insertions(+) diff --git a/fs/xfs/scrub/scrub.c b/fs/xfs/scrub/scrub.c index f1775bb19313..8ebf35b115ce 100644 --- a/fs/xfs/scrub/scrub.c +++ b/fs/xfs/scrub/scrub.c @@ -168,6 +168,7 @@ xchk_teardown( xfs_irele(sc->ip); sc->ip = NULL; } + sb_end_write(sc->mp->m_super); if (sc->flags & XCHK_REAPING_DISABLED) xchk_start_reaping(sc); if (sc->flags & XCHK_HAS_QUOTAOFFLOCK) { @@ -490,6 +491,14 @@ xfs_scrub_metadata( sc.ops = &meta_scrub_ops[sm->sm_type]; sc.sick_mask = xchk_health_mask_for_scrub_type(sm->sm_type); retry_op: + /* + * If freeze runs concurrently with a scrub, the freeze can be delayed + * indefinitely as we walk the filesystem and iterate over metadata + * buffers. Freeze quiesces the log (which waits for the buffer LRU to + * be emptied) and that won't happen while checking is running. + */ + sb_start_write(mp->m_super); + /* Set up for the operation. */ error = sc.ops->setup(&sc, ip); if (error) diff --git a/fs/xfs/xfs_fsmap.c b/fs/xfs/xfs_fsmap.c index 918456ca29e1..442fd4311f18 100644 --- a/fs/xfs/xfs_fsmap.c +++ b/fs/xfs/xfs_fsmap.c @@ -896,6 +896,14 @@ xfs_getfsmap( info.format_arg = arg; info.head = head; + /* + * If fsmap runs concurrently with a scrub, the freeze can be delayed + * indefinitely as we walk the rmapbt and iterate over metadata + * buffers. Freeze quiesces the log (which waits for the buffer LRU to + * be emptied) and that won't happen while we're reading buffers. + */ + sb_start_write(mp->m_super); + /* For each device we support... */ for (i = 0; i < XFS_GETFSMAP_DEVS; i++) { /* Is this device within the range the user asked for? */ @@ -935,6 +943,7 @@ xfs_getfsmap( if (tp) xfs_trans_cancel(tp); + sb_end_write(mp->m_super); head->fmh_oflags = FMH_OF_DEV_T; return error; } diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c index 3b208f9a865c..a65dc227e40d 100644 --- a/fs/xfs/xfs_trans.c +++ b/fs/xfs/xfs_trans.c @@ -306,6 +306,11 @@ xfs_trans_alloc( * * Note the zero-length reservation; this transaction MUST be cancelled * without any dirty data. + * + * Callers should obtain freeze protection to avoid two conflicts with fs + * freezing: (1) having active transactions trip the m_active_trans ASSERTs; + * and (2) grabbing buffers at the same time that freeze is trying to drain + * the buffer LRU list. */ int xfs_trans_alloc_empty(