Re: xfs blocks (blocked for more than 120 seconds)

["Michel Verbraak(1st-Setup)" <info@xxxxxxxxxxxx>]

op 24-03-14 18:36, Dave Chinner schreef:

On Mon, Mar 24, 2014 at 10:24:45AM +0100, Michel Verbraak(1st-Setup) wrote:

Hi,

We have a problem with one of our systems which is using XFS but we are
unable to find the problem. Recently we had two moments, Tuesday 4th of
March and Friday the 21st of March, where we had to reboot the system to
get it up and running again.

What happens:
- The programs handling files on the XFS disc stop working when
creating, deleting or writing files. They do not error they are just
waiting on the command to complete.
- One of our programs, a java application, goes into very high cpu usage
(50%) which normally is at 1%. This could be something in our java
application but it happens at the moment handling files gets stuck.
- A nice restart of the programs does not succeed as wel a kill -9 does
not work.
- Trying to reboot the servers in a normal fashion does not work. As it
is a virtual machine we have to do a shutdown (unplug power) and start
it up again to get it up and running.

......

Following details I have for you:

System OS: Ubuntu 12.04 LTS
Kernel: 3.2.0-37-generic #58-Ubuntu SMP Thu Jan 24 15:28:10 UTC 2013
x86_64 x86_64 x86_64 GNU/Linux
Server: Virtual machine in a VMWare setup.
Disc: 300GB direct attached LUN

We have an exact clone of this system for our acceptance environment. In
this environment we are unable to reproduce this problem/situation.

Differences between the two days is that our services on 2014-03-21 were
quit busy with a lot of file changes on the xfs disc and on 2014-03-04
the system was very quiet on the moment the kernel traces appear and the
services get stuck.

Any help is appreciated.

Regards Michel Verbraak.

Following we see in the syslog on both moments (2014-03-04 and 2014-03-21):

....

Mar 21 06:32:20 ealxs00169 kernel: [1412280.930543] flush-8:16      D
0000000000000000     0 13864      2 0x00000000
[<ffffffff8165b34f>] schedule+0x3f/0x60
[<ffffffff8165b3ff>] io_schedule+0x8f/0xd0
[<ffffffff8111836e>] sleep_on_page+0xe/0x20
[<ffffffff8165baca>] __wait_on_bit_lock+0x5a/0xc0
[<ffffffff81118357>] __lock_page+0x67/0x70
[<ffffffff81122bd4>] write_cache_pages+0x3d4/0x460
[<ffffffff81122caa>] generic_writepages+0x4a/0x70
[<ffffffffa007980d>] xfs_vm_writepages+0x4d/0x60 [xfs]
[<ffffffff81123b71>] do_writepages+0x21/0x40
[<ffffffff811a2990>] writeback_single_inode+0x180/0x430
[<ffffffff811a3056>] writeback_sb_inodes+0x1b6/0x270
[<ffffffff811a31ae>] __writeback_inodes_wb+0x9e/0xd0
[<ffffffff811a345b>] wb_writeback+0x27b/0x330
[<ffffffff811a35af>] wb_check_old_data_flush+0x9f/0xb0
[<ffffffff811a4481>] wb_do_writeback+0x151/0x1d0
[<ffffffff811a4583>] bdi_writeback_thread+0x83/0x2a0
[<ffffffff8108b27c>] kthread+0x8c/0xa0

Writeback is blocked on a locked page, and is waiting for IO
completion.

Mar 21 06:34:20 ealxs00169 kernel: [1412400.891181] archiver.pl     D
[<ffffffff8165b34f>] schedule+0x3f/0x60
[<ffffffff8165b995>] schedule_timeout+0x2a5/0x320
[<ffffffff8165c5f0>] __down_common+0xa5/0xf5
[<ffffffff8165c6b3>] __down+0x1d/0x1f
[<ffffffff810912e1>] down+0x41/0x50
[<ffffffffa007c0f4>] xfs_buf_lock+0x44/0x110 [xfs]
[<ffffffffa007c295>] _xfs_buf_find+0xd5/0x240 [xfs]
[<ffffffffa007c684>] xfs_buf_get+0x34/0x1c0 [xfs]
[<ffffffffa007cf2d>] xfs_buf_read+0x2d/0x120 [xfs]
[<ffffffffa00d89ff>] xfs_trans_read_buf+0x2bf/0x470 [xfs]
[<ffffffffa0094775>] xfs_read_agf+0x65/0x1a0 [xfs]
[<ffffffffa00948e2>] xfs_alloc_read_agf+0x32/0x60 [xfs]
[<ffffffffa00966ff>] xfs_alloc_fix_freelist+0x42f/0x490 [xfs]
[<ffffffffa0096802>] xfs_free_extent+0xa2/0x120 [xfs]
[<ffffffffa00a6e14>] xfs_bmap_finish+0x164/0x1b0 [xfs]
[<ffffffffa00c143b>] xfs_itruncate_extents+0xdb/0x1e0 [xfs]
[<ffffffffa00c15a6>] xfs_itruncate_data+0x66/0x150 [xfs]
[<ffffffffa009056e>] xfs_inactive+0x2fe/0x460 [xfs]
[<ffffffffa008afad>] xfs_fs_evict_inode+0xad/0x110 [xfs]
[<ffffffff81193e98>] evict+0xb8/0x1c0
[<ffffffff81194088>] iput_final+0xe8/0x210
[<ffffffff811941ee>] iput+0x3e/0x50
[<ffffffff81188be3>] do_unlinkat+0x153/0x1d0
[<ffffffff811897b6>] sys_unlink+0x16/0x20
[<ffffffff81665842>] system_call_fastpath+0x16/0x1b

120s later, unlinking a file, blocked waiting on an AGF lock.

Mar 21 06:34:20 ealxs00169 kernel: [1412400.891686] flush-8:16      D

writeback again, 120s later.

Mar 21 06:36:20 ealxs00169 kernel: [1412520.861471] java            D
[<ffffffff8165b995>] schedule_timeout+0x2a5/0x320
[<ffffffff8165c5f0>] __down_common+0xa5/0xf5
[<ffffffff8165c6b3>] __down+0x1d/0x1f
[<ffffffff810912e1>] down+0x41/0x50
[<ffffffffa007c0f4>] xfs_buf_lock+0x44/0x110 [xfs]
[<ffffffffa007c295>] _xfs_buf_find+0xd5/0x240 [xfs]
[<ffffffffa007c684>] xfs_buf_get+0x34/0x1c0 [xfs]
[<ffffffffa007cf2d>] xfs_buf_read+0x2d/0x120 [xfs]
[<ffffffffa00d89ff>] xfs_trans_read_buf+0x2bf/0x470 [xfs]
[<ffffffffa0094775>] xfs_read_agf+0x65/0x1a0 [xfs]
[<ffffffffa00948e2>] xfs_alloc_read_agf+0x32/0x60 [xfs]
[<ffffffffa00966ff>] xfs_alloc_fix_freelist+0x42f/0x490 [xfs]
[<ffffffffa0096a4b>] xfs_alloc_vextent+0x1cb/0x690 [xfs]
[<ffffffffa00a02c1>] xfs_bmap_btalloc+0x2b1/0x770 [xfs]
[<ffffffffa00a07a4>] xfs_bmap_alloc+0x24/0x40 [xfs]
[<ffffffffa00a594e>] xfs_bmapi_allocate+0xce/0x2d0 [xfs]
[<ffffffffa00a85c3>] xfs_bmapi_write+0x4c3/0x720 [xfs]
[<ffffffffa0086988>] xfs_iomap_write_allocate+0x178/0x330 [xfs]
[<ffffffffa00799c3>] xfs_map_blocks+0x183/0x250 [xfs]
[<ffffffffa007aa56>] xfs_vm_writepage+0x196/0x510 [xfs]
[<ffffffff81122217>] __writepage+0x17/0x40
[<ffffffff81122a0d>] write_cache_pages+0x20d/0x460
[<ffffffff81122caa>] generic_writepages+0x4a/0x70
[<ffffffffa007980d>] xfs_vm_writepages+0x4d/0x60 [xfs]
[<ffffffff81123b71>] do_writepages+0x21/0x40
[<ffffffff81119f2b>] __filemap_fdatawrite_range+0x5b/0x60
[<ffffffff81119f82>] filemap_write_and_wait_range+0x52/0x80
[<ffffffffa007f05d>] xfs_file_fsync+0x5d/0x300 [xfs]
[<ffffffff811a7eb6>] do_fsync+0x56/0x80
[<ffffffff811a81e0>] sys_fsync+0x10/0x20
[<ffffffff81665842>] system_call_fastpath+0x16/0x1b

120s later, fsync() blocks and AGF lock trying to do allocation.

Mar 21 06:36:20 ealxs00169 kernel: [1412520.862112] archiver.pl     D
[<ffffffff8165b34f>] schedule+0x3f/0x60
[<ffffffff8165b995>] schedule_timeout+0x2a5/0x320
[<ffffffff8165c5f0>] __down_common+0xa5/0xf5
[<ffffffff8165c6b3>] __down+0x1d/0x1f
[<ffffffff810912e1>] down+0x41/0x50
[<ffffffffa007c0f4>] xfs_buf_lock+0x44/0x110 [xfs]
[<ffffffffa007c295>] _xfs_buf_find+0xd5/0x240 [xfs]
[<ffffffffa007c684>] xfs_buf_get+0x34/0x1c0 [xfs]
[<ffffffffa007cf2d>] xfs_buf_read+0x2d/0x120 [xfs]
[<ffffffffa00d89ff>] xfs_trans_read_buf+0x2bf/0x470 [xfs]
[<ffffffffa0094775>] xfs_read_agf+0x65/0x1a0 [xfs]
[<ffffffffa00948e2>] xfs_alloc_read_agf+0x32/0x60 [xfs]
[<ffffffffa00966ff>] xfs_alloc_fix_freelist+0x42f/0x490 [xfs]
[<ffffffffa0096802>] xfs_free_extent+0xa2/0x120 [xfs]
[<ffffffffa00a6e14>] xfs_bmap_finish+0x164/0x1b0 [xfs]
[<ffffffffa00c143b>] xfs_itruncate_extents+0xdb/0x1e0 [xfs]
[<ffffffffa00c15a6>] xfs_itruncate_data+0x66/0x150 [xfs]
[<ffffffffa009056e>] xfs_inactive+0x2fe/0x460 [xfs]
[<ffffffffa008afad>] xfs_fs_evict_inode+0xad/0x110 [xfs]
[<ffffffff81193e98>] evict+0xb8/0x1c0
[<ffffffff81194088>] iput_final+0xe8/0x210
[<ffffffff811941ee>] iput+0x3e/0x50
[<ffffffff81188be3>] do_unlinkat+0x153/0x1d0
[<ffffffff811897b6>] sys_unlink+0x16/0x20
[<ffffffff81665842>] system_call_fastpath+0x16/0x1b

Still blocked on AGF in unlink.

Mar 21 06:38:20 ealxs00169 kernel: [1412640.821037] java            D
[<ffffffff8165b34f>] schedule+0x3f/0x60
[<ffffffff8165c157>] __mutex_lock_slowpath+0xd7/0x150
[<ffffffff8165bd6a>] mutex_lock+0x2a/0x50
[<ffffffff81188b1e>] do_unlinkat+0x8e/0x1d0
[<ffffffff811897b6>] sys_unlink+0x16/0x20
[<ffffffff81665842>] system_call_fastpath+0x16/0x1b

120s later, unlink blocked on a directory mutex.

(others stuck on AGF lock).

From this moment on the services are not working anymore. Complete stuck.

Yup, everything is stuck waiting for writeback to complete.

can you reproduce this? does the IO subsystem go idle when this
occurs? or is it running flat out?

We are not yet able to reproduce. But your added explanation might help us in reproducing. The production environment is very dynamic in when clients connect to the service and what kind of requests they do.

The colleague handling the incident tried to get some info but because he was alarmed quit late he decided for the reboot instead to get our production qorking again. For the next time we are preparing some scripts to gather information which might tell more.
If you have any suggestions on commands we can run when it happens again please let me know? Currently we are configuring kdump as suggested by Mark and some other queries against our own software.

Cheers,

Dave.

Some extra info: this system has been running for about 1 year without any problems. During this time it was never rebooted or restarted until the issue on the 4th. Only change could be in the usage of java service running on it by external clients. We are looking into this.

Thank you for looking into it.

Michel.

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