linux/fs/xfs/scrub
Darrick J. Wong 27fb5a72f5 xfs: prohibit fs freezing when using empty transactions
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@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
2020-03-26 08:19:24 -07:00
..
agheader_repair.c xfs: replace open-coded bitmap weight logic 2020-03-18 08:12:23 -07:00
agheader.c xfs: remove XFS_BUF_TO_SBP 2020-03-11 09:11:39 -07:00
alloc.c xfs: convert btree cursor ag-private member name 2020-03-13 10:37:14 -07:00
attr.c xfs: mark extended attr corrupt when lookup-by-hash fails 2020-03-12 07:58:13 -07:00
attr.h xfs: only allocate memory for scrubbing attributes when we need it 2019-07-05 10:29:56 -07:00
bitmap.c xfs: replace open-coded bitmap weight logic 2020-03-18 08:12:23 -07:00
bitmap.h xfs: replace open-coded bitmap weight logic 2020-03-18 08:12:23 -07:00
bmap.c xfs: convert btree cursor inode-private member names 2020-03-13 10:37:14 -07:00
btree.c xfs: remove unused header files 2019-06-28 19:30:43 -07:00
btree.h xfs: const-ify xfs_owner_info arguments 2018-12-12 08:47:16 -08:00
common.c xfs: remove unused header files 2019-06-28 19:30:43 -07:00
common.h xfs: periodically yield scrub threads to the scheduler 2019-11-07 13:00:53 -08:00
dabtree.c xfs: drop all altpath buffers at the end of the sibling check 2020-03-26 08:19:24 -07:00
dabtree.h xfs: refactor btree node scrubbing 2019-11-10 16:54:19 -08:00
dir.c xfs: directory bestfree check should release buffers 2020-03-26 08:19:24 -07:00
fscounters.c xfs: remove unnecessary null pointer checks from _read_agf callers 2020-01-26 14:32:27 -08:00
health.c xfs: fix missing header includes 2019-11-07 13:00:53 -08:00
health.h xfs: scrub should only cross-reference with healthy btrees 2019-04-16 10:01:57 -07:00
ialloc.c xfs: convert btree cursor ag-private member name 2020-03-13 10:37:14 -07:00
inode.c xfs: remove unused header files 2019-06-28 19:30:43 -07:00
parent.c xfs: allow parent directory scans to be interrupted with fatal signals 2019-11-27 08:23:14 -08:00
quota.c xfs: add missing early termination checks to record scrubbing functions 2019-11-06 08:07:41 -08:00
refcount.c xfs: convert btree cursor ag-private member name 2020-03-13 10:37:14 -07:00
repair.c xfs: rename xfs_bitmap to xbitmap 2020-03-18 08:12:23 -07:00
repair.h xfs: rename xfs_bitmap to xbitmap 2020-03-18 08:12:23 -07:00
rmap.c xfs: convert btree cursor ag-private member name 2020-03-13 10:37:14 -07:00
rtbitmap.c xfs: remove unused header files 2019-06-28 19:30:43 -07:00
scrub.c xfs: prohibit fs freezing when using empty transactions 2020-03-26 08:19:24 -07:00
scrub.h xfs: add online scrub for superblock counters 2019-04-30 08:19:13 -07:00
symlink.c fs: xfs: Remove KM_NOSLEEP and KM_SLEEP. 2019-08-26 12:06:22 -07:00
trace.c xfs: convert btree cursor inode-private member names 2020-03-13 10:37:14 -07:00
trace.h xfs: convert btree cursor inode-private member names 2020-03-13 10:37:14 -07:00
xfs_scrub.h xfs: convert to SPDX license tags 2018-06-06 14:17:53 -07:00