[linux-lvm] disabling udev_sync and udev_rules

[Steven Dake (stdake)]

On 3/15/16, 3:56 PM, "linux-lvm-bounces at redhat.com on behalf of Zdenek
Kabelac" <linux-lvm-bounces at redhat.com on behalf of
zdenek.kabelac at gmail.com> wrote:

>Dne 15.3.2016 v 23:31 Serguei Bezverkhi (sbezverk) napsal(a):
>> Hello folks,
>>
>> While trying to make lvm work within a docker container I came across
>>an issue when all lvcreate/lvremove got stuck indefinetly or until
>>control-c. When I checked process I noticed lvm was waiting on one
>>semaphore, I found that other folks hit similar issue and they fixed it
>>by setting  udev_sync and udev_rules to 0. It also helped my case too.
>>
>> I would greatly appreciate if you could share your thought if this
>>change in future can potentially have any negative impact.
>>
>> Thank you
>
>Hi
>
>
>To 'unblock' stuck processes waiting on udev cookie - you could run:
>
>'dmsetup udevcomplete_all'
>
>
>However the key question is - how you could get stuck.
>That may need further debugging.
>
>You would need to expose your OS  version and also version of lvm2 in use.
>
>Non working cookies are bad - and disabling udev sync is even more bad
>idea...

Zdeknek,

To expand on what Serguei is doing, he is working on a patch to add
LVM2+Iscsi in a container for the Cinder (block storage AAS) project in
OpenStack.  He is doing this in the upstream repository here:

http://github.com/openstack/klla

The LVM processes are running within a container.  I suspect if the
process is stuck on a semaphore it has something to do with semaphores not
being shared with the host OS, because containers naturally create a
contained environment.  There are solutions for things like sockets, but
not necessarily for things like semaphores for the container to
communicate with the host OS.

Is there another mechanism besides semaphores to get lvm2 to communicate
with udev?  Turning off udev sync side-steps the problem because then udev
is not in the picture.  Some people in our community think this is a
security risk, although we assume the servers are completely secure.

Your advice welcome on how to solve the problem would be mighty nice :)

To see the change in full, check out:

https://review.openstack.org/#/c/291285/


Regards,
-steve

>
>Regards
>
>Zdenek
>
>
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