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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 78962C43331 for ; Wed, 25 Mar 2020 23:26:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5622520714 for ; Wed, 25 Mar 2020 23:26:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727402AbgCYX0p (ORCPT ); Wed, 25 Mar 2020 19:26:45 -0400 Received: from mail105.syd.optusnet.com.au ([211.29.132.249]:42819 "EHLO mail105.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727395AbgCYX0p (ORCPT ); Wed, 25 Mar 2020 19:26:45 -0400 Received: from dread.disaster.area (pa49-195-110-5.pa.nsw.optusnet.com.au [49.195.110.5]) by mail105.syd.optusnet.com.au (Postfix) with ESMTPS id D349E3A3017; Thu, 26 Mar 2020 10:26:41 +1100 (AEDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1jHFQ0-0005aY-Bx; Thu, 26 Mar 2020 10:26:40 +1100 Date: Thu, 26 Mar 2020 10:26:40 +1100 From: Dave Chinner To: "Darrick J. Wong" Cc: linux-xfs@vger.kernel.org Subject: Re: [PATCH v2 1/4] xfs: prohibit fs freezing when using empty transactions Message-ID: <20200325232640.GL10776@dread.disaster.area> References: <158510667039.922633.6138311243444001882.stgit@magnolia> <158510667670.922633.9371387481128286027.stgit@magnolia> <20200325060627.GW29339@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200325060627.GW29339@magnolia> User-Agent: Mutt/1.10.1 (2018-07-13) X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.3 cv=W5xGqiek c=1 sm=1 tr=0 a=UL8WcDbXXJQENuhYI/M0Yg==:117 a=UL8WcDbXXJQENuhYI/M0Yg==:17 a=jpOVt7BSZ2e4Z31A5e1TngXxSK0=:19 a=kj9zAlcOel0A:10 a=SS2py6AdgQ4A:10 a=yPCof4ZbAAAA:8 a=20KFwNOVAAAA:8 a=7-415B0cAAAA:8 a=eFAJVGdYXRnGeneTAcIA:9 a=CjuIK1q_8ugA:10 a=biEYGPWJfzWAr4FL6Ov7:22 Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Tue, Mar 24, 2020 at 11:06:27PM -0700, Darrick J. Wong wrote: > 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 Looks good now. Reviewed-by: Dave Chinner -- Dave Chinner david@fromorbit.com