Re: Disk error, then endless loop

[Chris Dunlop <chris@onthe.net.au>]

On Tue, Nov 17, 2015 at 12:37:24PM -0500, Brian Foster wrote:
> On Wed, Nov 18, 2015 at 03:28:02AM +1100, Chris Dunlop wrote:
>> On Tue, Nov 17, 2015 at 07:41:48AM -0500, Brian Foster wrote:
>>> On Tue, Nov 17, 2015 at 07:03:33PM +1100, Chris Dunlop wrote:
>>>> I tried to umount the filesystem but the umount is now hung and unkillable:
>>>> 
>>>> # ps -ostat,wchan='WCHAN-xxxxxxxxxxxxxxxxxx',cmd -C umount
>>>> STAT WCHAN-xxxxxxxxxxxxxxxxxx CMD
>>>> D+   xfs_ail_push_all_sync    umount /var/lib/ceph/osd/ceph-18
>>> 
>>> ... but it appears you still have something pending in the AIL which is
>>> holding everything up. The most likely case is an EFI/EFD item hanging
>>> around from an extent free operation, as this was a known issue,
>>> particularly on fs shutdowns. Fixes for this went into the v4.3 kernel.
>> 
>> Any chance of these fixes getting into -stable, or are they too intrusive
>> and/or depend on other intrusive changes?
> 
> I don't think so... it was a multi-patch series and a rework of the
> EFI/EFD reference counting as opposed to an isolated bug fix. For
> reference, it was commits 5e4b538 through f0b2efa or so.

...

>>> Does the umount process actually appear to be doing anything? E.g., are
>>> you seeing noticeable CPU load or I/O errors continue to the logs, or
>>> has everything pretty much locked up? You could also enable tracepoints
>>> (trace-cmd start -e "xfs:*"; cat /sys/kernel/debug/tracing/trace_pipe)
>>> to get a quick idea of what's going on.
>> 
>> No, the umount hasn't done anything noticable in the past 6.5 hours:
>> 
>> b2# date; ps -opid,lstart,time,stat,wchan='WCHAN-xxxxxxxxxxxxxxxxxx',cmd -C umount
>> Wed Nov 18 03:08:30 AEDT 2015
>>   PID                  STARTED     TIME STAT WCHAN-xxxxxxxxxxxxxxxxxx CMD
>> 23946 Tue Nov 17 17:30:41 2015 00:00:00 D+   xfs_ail_push_all_sync    umount /var/lib/ceph/osd/ceph-18
>> 
>> I don't know how to interpret the tracepoints, but there are other busy
>> XFS filesystems on the box so that's cluttering things up. For what it's
>> worth, it appears the original device (/dev/sdu1) was previously dev
>> 65:65:
>> 
>> b2# ls -l /dev/sd[tuv]{,1}
>> brw-rw---T 1 root disk 65, 48 Sep 16 17:11 /dev/sdt
>> brw-rw---T 1 root disk 65, 49 Sep 16 17:11 /dev/sdt1
>> brw-rw---T 1 root disk 65, 80 Oct 30 15:38 /dev/sdv
>> brw-rw---T 1 root disk 65, 81 Oct 30 15:40 /dev/sdv1
>> 
>> ..and in 10 seconds of /sys/kernel/debug/tracing/trace_pipe we have:
>> 
>> # grep 'dev 65:65' /sys/kernel/debug/tracing/trace_pipe > /tmp/x1 & sleep 10; kill $!
>> # wc -l /tmp/x1
>> 181953 /tmp/x1
>> # head /tmp/x1
>>            <...>-7702  [012] .... 5392362.786946: xfs_buf_item_iodone_async: dev 65:65 bno 0x1828eed18 nblks 0x8 hold 2 pincount 0 lock 0 flags ASYNC|DONE|PAGES caller xfs_buf_ioend [xfs]
>>            <...>-7702  [012] .... 5392362.786946: xfs_buf_ioerror: dev 65:65 bno 0x1828eed18 len 0x1000 hold 2 pincount 0 lock 0 error 0 flags ASYNC|DONE|PAGES caller xfs_buf_iodone_callbacks [xfs]
>>     xfsaild/sdu1-7991  [005] .N.. 5392363.647059: xfs_buf_submit: dev 65:65 bno 0x27ffffff8 nblks 0x8 hold 2 pincount 0 lock 0 flags WRITE|ASYNC|DONE|PAGES caller __xfs_buf_delwri_submit [xfs]
>>     xfsaild/sdu1-7991  [005] .N.. 5392363.647059: xfs_buf_hold: dev 65:65 bno 0x27ffffff8 nblks 0x8 hold 2 pincount 0 lock 0 flags WRITE|ASYNC|DONE|PAGES caller xfs_buf_submit [xfs]
>>     xfsaild/sdu1-7991  [005] .N.. 5392363.647061: xfs_buf_rele: dev 65:65 bno 0x27ffffff8 nblks 0x8 hold 3 pincount 0 lock 0 flags WRITE|ASYNC|DONE|PAGES caller xfs_buf_submit [xfs]
>>     xfsaild/sdu1-7991  [005] .N.. 5392363.647061: xfs_buf_submit: dev 65:65 bno 0x280006398 nblks 0x8 hold 2 pincount 0 lock 0 flags WRITE|ASYNC|DONE|PAGES caller __xfs_buf_delwri_submit [xfs]
>>     xfsaild/sdu1-7991  [005] .N.. 5392363.647061: xfs_buf_hold: dev 65:65 bno 0x280006398 nblks 0x8 hold 2 pincount 0 lock 0 flags WRITE|ASYNC|DONE|PAGES caller xfs_buf_submit [xfs]
>>     xfsaild/sdu1-7991  [005] .N.. 5392363.647063: xfs_buf_rele: dev 65:65 bno 0x280006398 nblks 0x8 hold 3 pincount 0 lock 0 flags WRITE|ASYNC|DONE|PAGES caller xfs_buf_submit [xfs]
>>     xfsaild/sdu1-7991  [005] .N.. 5392363.647063: xfs_buf_submit: dev 65:65 bno 0x2800063f8 nblks 0x8 hold 2 pincount 0 lock 0 flags WRITE|ASYNC|DONE|PAGES caller __xfs_buf_delwri_submit [xfs]
>>     xfsaild/sdu1-7991  [005] .N.. 5392363.647064: xfs_buf_hold: dev 65:65 bno 0x2800063f8 nblks 0x8 hold 2 pincount 0 lock 0 flags WRITE|ASYNC|DONE|PAGES caller xfs_buf_submit [xfs]
>> 
> 
> Hmm, that is notably more activity than I recall when reproducing the
> original AIL issue. Do we know whether the filesystem had actually shut
> down or is in some intermediate state looping on errors? The fact that
> it continues to try and submit I/O suggests that perhaps it hasn't shut
> down for whatever reason.
> 
> If the device has already dropped and reconnected as a new dev node,
> it's probably harmless at this point to just try to forcibly shut down
> the fs on the old one. Could you try the following?
> 
>   xfs_io -x -c shutdown <mnt>

# xfs_io -x -c shutdown /var/lib/ceph/osd/ceph-18
foreign file active, shutdown command is for XFS filesystems only

# grep ceph-18 /etc/mtab
  <<< crickets >>>

I don't know when the fs disappeared from mtab, it could have been when I
first did the umount I guess, I didn't think to check at the time. But the
umount is still there:

# date; ps -opid,lstart,time,stat,wchan='WCHAN-xxxxxxxxxxxxxxxxxx',cmd -C umount
Wed Nov 18 06:23:21 AEDT 2015
  PID                  STARTED     TIME STAT WCHAN-xxxxxxxxxxxxxxxxxx CMD
23946 Tue Nov 17 17:30:41 2015 00:00:00 D+   xfs_ail_push_all_sync    umount /var/lib/ceph/osd/ceph-18

> Can you unmount the fs after that? If not, is there still any tracepoint
> activity on the old device?
> 
> Brian

The activity is still ongoing on the old device:

# trace-cmd start -e "xfs:*"
/sys/kernel/debug/tracing/events/xfs/*/filter
# grep 'dev 65:65' /sys/kernel/debug/tracing/trace_pipe > /tmp/y1 & sleep 10; kill $!; wc -l /tmp/y1
129573 /tmp/y1

Doing my little sed and perl dance shows it's still the same set of 188
blocks as mentioned before.

Chris

>> In the 181953 lines there's a set of 188 different block numbers
>> appearing, ranging from 0x8 to 0x2900ffbd8:
>> 
>> # sed -rn 's/.*bno (0x[[:xdigit:]]+).*/\1/p' /tmp/x1 | sort -u > /tmp/x2
>> # wc -l /tmp/x2
>> 188 /tmp/x2
>> # perl -pe 's/(.*)/hex($1)/e' /tmp/x2 | sort -n | perl -ne 'printf "0x%x\n",$_' > /tmp/x3
>> # head /tmp/x3
>> 0x8
>> 0x10
>> 0x20
>> 0x28
>> 0x3188
>> 0x4a40
>> 0x4a68
>> 0x2b163a0
>> 0x31fecd0
>> 0x426e8f8
>> b2# tail /tmp/x3
>> 0x2900ffb78
>> 0x2900ffb88
>> 0x2900ffb98
>> 0x2900ffba8
>> 0x2900ffbb0
>> 0x2900ffbb8
>> 0x2900ffbc0
>> 0x2900ffbc8
>> 0x2900ffbd0
>> 0x2900ffbd8
>> 
>>>> As previously mentioned, the disk has actually reappeared under a different
>>>> /dev/sdXX name (it was sdu, now sdbh). Trying to mount the disk (read only)
>>>> results in:
>>>> 
>>>> # mkdir /mnt/xfs && mount -ologdev=/dev/md8p5,ro /dev/sdbh1 /mnt/xfs
>>>> mount: /dev/sdbh1 already mounted or /mnt/xfs busy
>>> 
>>> Probably due to either a uuid check or blocking on access to the
>>> external log device. You'll probably need to clean up the stale mount
>>> before this will work.
>>> 
>>> As it is, something is clearly wrong with the drive. I can't really
>>> interpret the I/O errors and whatnot (linux-scsi?), but you probably
>>> want to look into health assessment tools (e.g., smart) to get an idea
>>> of what's wrong and/or replace the device and restore from backups (or
>>> perhaps heal via the ceph cluster, in your case).
>> 
>> Sure. It's not the disk that's concerning me, they're expected to die,
>> but it looks like the disk error has put XFS in a state where the only
>> solution is a hard power cycle (after quiescing and cleaning up what I
>> can): I haven't tried it yet, but I expect I won't be able reboot
>> cleanly.
>> 
>>> 
>>> Brian
>> 
>> Cheers,
>> 
>> Chris

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