Re: constant array_state active after specific jobs

[pdi <pdi@otenet.gr>]

On Fri, 24 Mar 2017 16:25:35 +1100
NeilBrown <neilb@suse.com> wrote:

> On Thu, Mar 23 2017, pdi wrote:
> 
> > Greetings all,
> >
> > The problem in a nutshell is that an array is clean after boot,
> > until some specific jobs switch it to active where it remains until
> > reboot.
> >
> > A similar problem was discussed, and solved, in 
> > https://www.spinics.net/lists/raid/msg46450.html. However, AFAICT,
> > it is not the same issue.
> >
> > I would be grateful for any insights as to why this happens and/or
> > how to prevent it.
> >
> > The relevant info follows, please let me know if anything further
> > might help.
> >
> > Many thanks in advance.
> >
> > - uname -a
> >   Linux hostname 4.4.38 #1 SMP Sun Dec 11 16:03:41 CST 2016 x86_64
> >   Intel(R) Core(TM)2 Duo CPU E8400 @ 3.00GHz GenuineIntel GNU/Linux
> > - mdadm -V
> >   mdadm - v3.3.4 - 3rd August 2015
> > - Desktop drives without sct/erc,
> >   with timeout mismatch correction as per
> >   https://raid.wiki.kernel.org/index.php/Timeout_Mismatch
> > - /dev/md9 is a raid10 array, 4 devices, far=2,
> >   with various dirs used as samba and nfs shares
> > - The array is in *constant* array_state active
> > - mdadm -D /dev/md9 | grep 'State :'
> >   State : active
> > - cat /sys/block/md9/md/array_state
> >   active
> > - watch -d 'grep md9 /proc/diskstats'
> >   remain unchanged
> > - uptime
> >   load average: 0.00, 0.00, 0.00
> > - cat /sys/block/md9/md/safe_mode_delay
> >   0.201
> > - echo 0.1 > /sys/block/md9/md/safe_mode_delay
> >   array_state remains active
> > - echo clean > /sys/block/md9/md/array_state
> >   echo: write error: Device or resource busy
> > - reboot (with or without prior check)
> >   array_state clean
> > - After reboot, array remains clean until some specific
> >   jobs put it in constant active state. Such jobs so far
> >   identified:
> >   - echo check > /sys/block/md9/md/sync_action
> >   - run an rsnapshot job
> >   - start a qemu/kvm vm
> > - Other jobs, like text/doc editing, multimedia playback,
> >   etc retain array_state clean  
> 
> This bug was introduced by
> Commit: 20d0189b1012 ("block: Introduce new bio_split()")
> in 3.14, and fixed by
> Commit: 9b622e2bbcf0 ("raid10: increment write counter after bio is
> split") in 4.8.
> 
> Maybe the latter patch should be sent to -stable ??
> 
> NeilBrown

NeilBrown, thank you for your swift and concise answer.

I gather you are referring to kernel version numbers. The described
behaviour was first noticed many months ago with kernel 2.6.37.6, and
persisted after a system upgrade and kernel 4.4.38. However, after the
upgrade two things were corrected, the timeout mismatch, and a
Current_Pending_Sector in one of the drives; which may, or may not,
explain the occurrence with the older kernel.

Is this constant active state in the data array something to worry about
and try kernel >= 4.8, or shall I let be?

pdi