Re: [Suggestion] kernel: cgroup: mount failure in LTP cgroup_regression_test.sh

[Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>]

> ----- Original Message -----
>> From: "Tejun Heo" <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
>> To: "Jan Stancek" <jstancek-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
>> Cc: "Chen Gang" <gang.chen.5i5j-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, "Garrett Cooper" <yanegomi-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, gaowanlong-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org,
>> chris-8NJIiSa5LzA@public.gmane.org, mitani-Czb31pHLG9l3+QwDJ9on6Q@public.gmane.org, lizf-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org, "Li Zefan" <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>,
>> containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
>> Sent: Thursday, 21 November, 2013 4:26:45 PM
>> Subject: Re: [Suggestion] kernel: cgroup: mount failure in LTP cgroup_regression_test.sh
>>
>> Hello, Jan.
>>
>> On Thu, Nov 21, 2013 at 03:04:54AM -0500, Jan Stancek wrote:
>>> it looks like those 2 subsystems are already mounted by systemd,
>>> each in different hierarchy:
>>>
>>>>   cpuacct	4	35	1
>>>>   freezer	5	4	1
>>>
>>> from Documentation/cgroups/cgroups.txt:
>>> "If an active hierarchy with exactly the same set of subsystems already
>>> exists, it will be reused for the new mount. If no existing hierarchy
>>> matches, and any of the requested subsystems are in use in an existing
>>> hierarchy, the mount will fail with -EBUSY. Otherwise, a new hierarchy
>>> is activated, associated with the requested subsystems."
>>
>> Ah, cgroup now requires that those recycled mounts to have matching
>> options.  This is an intended behavior change because previously we
>> could end up with mounts which have actual options which differ from
>> what was specified by mount, which can be misleading at the very
>> least.
> 
> I believe the test always respected this requirement. Problem we see
> is because of initial state of the system. Test appears to expect
> that it is able to mount cgroups freely, but they are already in use.
> 
>> Would it be possible to update LTP accordingly?
> 
> I'm not sure the test can do anything (other than not run at all).
> 
> Other option is to setup system in a way where cgroups are not in use
> prior to running this test, though this may not be possible with systemd.
> 

I believe each test will do cleanup after it finishes (like umount
cgroupfs). I guess the system already mounted cgroupfs after boot
and each cgroup subsystem was mounted separately? And that leads to
this issue.