Re: constant array_state active after specific jobs

[NeilBrown <neilb@suse.com>]

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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

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