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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,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 955CAC1975A for ; Wed, 25 Mar 2020 04:54:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 769652076E for ; Wed, 25 Mar 2020 04:54:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726043AbgCYEx7 (ORCPT ); Wed, 25 Mar 2020 00:53:59 -0400 Received: from mail105.syd.optusnet.com.au ([211.29.132.249]:37625 "EHLO mail105.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725781AbgCYEx7 (ORCPT ); Wed, 25 Mar 2020 00:53:59 -0400 Received: from dread.disaster.area (pa49-195-202-68.pa.nsw.optusnet.com.au [49.195.202.68]) by mail105.syd.optusnet.com.au (Postfix) with ESMTPS id 744A23A3D8E; Wed, 25 Mar 2020 15:53:55 +1100 (AEDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1jGy37-0007Kl-UM; Wed, 25 Mar 2020 15:53:53 +1100 Date: Wed, 25 Mar 2020 15:53:53 +1100 From: Dave Chinner To: "Darrick J. Wong" Cc: linux-xfs@vger.kernel.org Subject: Re: [PATCH 1/4] xfs: prohibit fs freezing when using empty transactions Message-ID: <20200325045353.GF10776@dread.disaster.area> 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/1.10.1 (2018-07-13) X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.3 cv=X6os11be c=1 sm=1 tr=0 a=mqTaRPt+QsUAtUurwE173Q==:117 a=mqTaRPt+QsUAtUurwE173Q==:17 a=jpOVt7BSZ2e4Z31A5e1TngXxSK0=:19 a=kj9zAlcOel0A:10 a=SS2py6AdgQ4A:10 a=yPCof4ZbAAAA:8 a=7-415B0cAAAA:8 a=LA7rwxcVcRJwNdo-CiwA: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 08:24:36PM -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. Makes sense. Minor nits: > > Signed-off-by: Darrick J. Wong > --- > fs/xfs/scrub/scrub.c | 4 ++++ > fs/xfs/xfs_fsmap.c | 4 ++++ > fs/xfs/xfs_trans.c | 5 +++++ > 3 files changed, 13 insertions(+) > > > diff --git a/fs/xfs/scrub/scrub.c b/fs/xfs/scrub/scrub.c > index f1775bb19313..a42bb66b335d 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 +491,9 @@ 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: > + /* Avoid conflicts with fs freeze. */ > + sb_start_write(mp->m_super); > + Rather than saying something realtively meaningless like "avoid conflicts with freeze", wouldn't it be better to say something like: /* * 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 runs. */ > /* 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..2bb2cd1e63cf 100644 > --- a/fs/xfs/xfs_fsmap.c > +++ b/fs/xfs/xfs_fsmap.c > @@ -896,6 +896,9 @@ xfs_getfsmap( > info.format_arg = arg; > info.head = head; > > + /* Avoid conflicts with fs freeze. */ > + sb_start_write(mp->m_super); > + And a similar comment here? -Dave. -- Dave Chinner david@fromorbit.com