Re: Disk error, then endless loop

Brian Foster
2015-11-17T20:35:02Z

On Tue, Nov 17, 2015 at 03:21:31PM -0500, Brian Foster wrote:
> On Wed, Nov 18, 2015 at 06:35:34AM +1100, Chris Dunlop wrote:
> > 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
> >
>
> Ah, so it's already been removed from the namespace. Apparently it's
> stuck at some point after the mount is made inaccessible and before it
> actually finishes with I/O. I'm not sure we have any other option other
> than a reset at this point, unfortunately. :/
>
> Brian
>

One last thought... it occurred to me that scsi devs have a delete
option under the /sysfs fs. Does the old/stale device still exist under
/sys/block/<dev>? If so, perhaps an 'echo 1 >
/sys/block/<dev>/device/delete' would move things along..?

Note that I have no idea what effect that will have beyond removing the
device node (so if it is still accessible now, it probably won't be
after that command). I just tried it while doing I/O to a test device
and it looked like it caused an fs shutdown, so it could be worth a try
as a last resort before a system restart.

Brian

> > > 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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