Re: /sys/block/md126 still exists even after stopping the array

[Artur Paszkiewicz <artur.paszkiewicz@intel.com>]

On 07/24/2014 03:40 PM, Sebastian Parschauer wrote:
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> On 25.06.2014 03:03, NeilBrown wrote:
>> On Tue, 24 Jun 2014 17:38:30 +0200 Francis Moreau
>> <francis.moro@gmail.com> wrote:
>>
>>> Hello,
>>>
>>> I'm having the folloing behaviour with kernel 3.14.5 and mdadm
>>> v3.3.1.
>>>
>>> After stopping all arrays, I still can see one of them in
>>> /sys/block/:
>>>
>>> # cat /proc/mdstat Personalities : [raid1] md125 : active raid1
>>> sdb3[1] sda3[0] 483688448 blocks super 1.2 [2/2] [UU] 
>>> [======>..............]  resync = 34.9% (169161280/483688448) 
>>> finish=44.0min speed=118852K/sec bitmap: 3/4 pages [12KB],
>>> 65536KB chunk
>>>
>>> md126 : active raid1 sdb2[1] sda2[0] 4038656 blocks super 1.2
>>> [2/2] [UU]
>>>
>>> md127 : active raid1 sdb1[1] sda1[0] 524224 blocks super 1.0
>>> [2/2] [UU]
>>>
>>> unused devices: <none>
>>>
>>> # mdadm --stop /dev/md12[567] mdadm: stopped /dev/md125 mdadm:
>>> stopped /dev/md126 mdadm: stopped /dev/md127
>>>
>>> # cat /proc/mdstat Personalities : [raid1] unused devices:
>>> <none>
>>>
>>> # ls /sys/block/ md126  sda  sdb  sdc  sr0
>>>
>>> # ls /sys/block/md126/md/ array_size  array_state  bitmap
>>> chunk_size  component_size  layout level  max_read_errors
>>> metadata_version  new_dev  raid_disks reshape_direction
>>> reshape_position  resync_start  safe_mode_delay
>>>
>>> # dmesg .... [ 1573.715476] md125: detected capacity change from
>>> 495296970752 to 0 [ 1573.715626] md: md125 stopped. [
>>> 1573.715633] md: unbind<sdb3> [ 1573.740681] md:
>>> export_rdev(sdb3) [ 1573.740694] md: unbind<sda3> [ 1573.754008]
>>> md: export_rdev(sda3) [ 1573.773398] md126: detected capacity
>>> change from 4135583744 to 0 [ 1573.773403] md: md126 stopped. [
>>> 1573.773410] md: unbind<sdb2> [ 1573.820652] md:
>>> export_rdev(sdb2) [ 1573.820664] md: unbind<sda2> [ 1573.873974]
>>> md: export_rdev(sda2) [ 1573.889904] md127: detected capacity
>>> change from 536805376 to 0 [ 1573.889910] md: md127 stopped. [
>>> 1573.889917] md: unbind<sdb1> [ 1573.913978] md:
>>> export_rdev(sdb1) [ 1573.914033] md: unbind<sda1> [ 1573.940627]
>>> md: export_rdev(sda1)
>>>
>>> After waiting a couple of min, stopping again md126 worked:
>>>
>>> [ 1835.755661] md: md126 stopped.
>>>
>>> Is this expected ?
>>
>> No overly surprising.
>>
>> This is probably caused by udev, or something udev runs, opening
>> /dev/md126 after it has been stopped.  This has the effect of
>> creating an empty inactive array. e.g.
>>
>> mknod /dev/test b 9 57 < /dev/test
>>
>> will make /sys/block/md57 appear.
>>
>> It is a bit untidy, but shouldn't cause problems.
>>
>> NeilBrown
>>
> 
> 
> Hi Neil,
> 
> we are also noticing this issue with udev-215 on Gentoo. They've
> switched over to systemd. Deactivating all udev rules doesn't help. So
> it must be an issue in the code. udev-204 works fine.
> When stopping udev, then it is possible to stop the MD array and it
> remains stopped (/sys/block/mdX disappears). Looks like they do
> something really strange there.
> 
> Do you have any advice how to fix this in another way but to change
> the kernel or to downgrade udev?
> 
> File a systemd bug?

Hi,

I have also noticed this issue. It is caused by this change in udev:

commit 3ebdb81ef088afd3b4c72b516beb5610f8c93a0d
Author: Kay Sievers <kay at vrfy.org>
Date:   Sun Apr 13 19:54:27 2014 -0700

     udev: serialize/synchronize block device event handling with file locks

http://cgit.freedesktop.org/systemd/systemd/commit/?id=3ebdb81ef088afd3b4c72b516beb5610f8c93a0d

It seems that they have already disabled this for dm for some reason,
but not for md:

commit e918a1b5a94f270186dca59156354acd2a596494
Author: Kay Sievers <kay@vrfy.org>
Date:   Tue Jun 3 16:49:38 2014 +0200

    udev: exclude device-mapper from block device ownership event locking

http://cgit.freedesktop.org/systemd/systemd/commit/?id=e918a1b5a94f270186dca59156354acd2a596494


Artur