On Tue, Mar 24, 2020 at 11:06:27PM -0700, Darrick J. Wong wrote: > From: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > > 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 <darrick.wong@xxxxxxxxxx> > --- > v2: improve comments Looks good now. Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx> -- Dave Chinner david@xxxxxxxxxxxxx
