Hi,
Sorry, I'm not trying to beat a dead horse here, but I do feel
something has changed... I just tested with Linux 4.5.2 and when
stopping an md array (with mdadm --stop) the entry in /sys/block/ is
removed, and even the /dev/mdXXX and /dev/md/name link are removed
properly.
When testing with Linux 4.9-rc3, the entries in /sys/block/ still
remain (array_state attribute value is "clear") after using mdadm
--stop and the /dev/mdXXX device exists (the /dev/md/name link is
removed, by udev I assume).
Looks like Linux 4.9 is at rc6 now -- have there been any changes that
would correct this behavior? Or is this expected behavior with the
latest version? Not sure when this changed, but I did go back to 4.5.2
and confirmed everything is removed correctly in that version, not
sure if this is different starting in 4.9, or something between 4.5
and 4.9.
Can anyone else confirm with Linux 4.9 that the /sys/block/mdXXX entry
lingers after using mdadm --stop? I suppose it could be some other
system that is causing this on my machines. I tested using the latest
from the master branch of mdadm and get the same result.
Thanks for your time and help.
--Marc
On Mon, Nov 21, 2016 at 9:08 AM, Marc Smith <marc.smith@xxxxxxx> wrote:
> On Sun, Nov 20, 2016 at 10:42 PM, NeilBrown <neilb@xxxxxxxx> wrote:
>> On Sat, Nov 19 2016, Marc Smith wrote:
>>
>>> On Mon, Nov 7, 2016 at 12:44 AM, NeilBrown <neilb@xxxxxxxx> wrote:
>>>> On Sat, Nov 05 2016, Marc Smith wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> It may be that I've never noticed this before, so maybe its not a
>>>>> problem... after using '--stop' to deactivate/stop an MD array, there
>>>>> are remnants of it lingering, namely an entry in /sys/block (eg,
>>>>> /sys/block/md127) and the device node in /dev remains (eg,
>>>>> /dev/md127).
>>>>>
>>>>> Is this normal? Like I said, it probably is, and I've just never
>>>>> noticed it before. I assume its not going to hurt anything, but is
>>>>> there a way to clean it up, without rebooting? Obviously I could
>>>>> remove the /dev entry, but what about /sys/block?
>>>>>
>>>>
>>>> You can remove them both by running
>>>> mdadm -S /dev/md127
>>>>
>>>> but they'll probably just reappear again.
>>>>
>>>> This seems to be an on-going battle between md and udev. I've "fixed"
>>>> it at least once, but it keeps coming back.
>>>>
>>>> When md removes the md127 device, a message is sent to udev.
>>>> As part of its response to this message, udev tries to open /dev/md127.
>>>> Because of the rather unusual way that md devices are created (it made
>>>> sense nearly 20 years ago when it was designed), opening /dev/md127
>>>> causes md to create device md127 again.
>>>>
>>>> You could
>>>> mv /dev/md127 /dev/md127X
>>>> mdadm -S /dev/md127X
>>>> rm /dev/md127X
>>>> that stop udev from opening /dev/md127. It seems to work reliably.
>>>>
>>>> md used to generate a CHANGE event before the REMOVE event, and only the
>>>> CHANGE event caused udev to open the device file. I removed that and
>>>> the problem went away. Apparently some change has happened to udev and
>>>> now it opens the file in response to REMOVE as well.
>>>
>>> I used "udevadm monitor -pku" to watch the events when running "mdadm
>>> --stop /dev/md127" and this is what I see:
>>>
>>> --snip--
>>> KERNEL[163074.119778] change /devices/virtual/block/md127 (block)
>>> ACTION=change
>>> DEVNAME=/dev/md127
>>> DEVPATH=/devices/virtual/block/md127
>>> DEVTYPE=disk
>>> MAJOR=9
>>> MINOR=127
>>> SEQNUM=3701
>>> SUBSYSTEM=block
>>>
>>> UDEV [163074.121569] change /devices/virtual/block/md127 (block)
>>> ACTION=change
>>> DEVNAME=/dev/md127
>>> DEVPATH=/devices/virtual/block/md127
>>> DEVTYPE=disk
>>> MAJOR=9
>>> MINOR=127
>>> SEQNUM=3701
>>> SUBSYSTEM=block
>>> SYSTEMD_READY=0
>>> USEC_INITIALIZED=370470
>>> --snip--
>>>
>>> I don't see any 'remove' event generated. I should mention if I hadn't
>>> already that I'm testing md-cluster (--bitmap=clustered), and
>>> currently using Linux 4.9-rc3.
>>
>> What version of mdadm are you using?
>
> v3.4
>
>
>> You need one which contains
>> Commit: 229e66cb9689 ("Manage.c: Only issue change events for kernels older than 2.6.28")
>>
>> which hasn't made it into a release yet. But if you are playing with
>> md-cluster, I would guess you are using the latest from git...
>
> Wasn't, but I will now. Thanks.
>
> --Marc
>
>
>>
>> NeilBrown
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