[Devel] Re: cgroup tasks file error

[Jue Hong]

Have you mounted the ns subsys?
The ns subsys will place some restrictions on the task movement.

On Tue, Dec 14, 2010 at 3:28 PM, ccmail111 <ccmail111 at yahoo.com> wrote:
>
> Thanks Matt.
> After doing what Serge suggests, I was able to create a dummy cgroup and
> move task (#580) below to the group. But now..
> I see another issue: cannot move the task back to its parent (root), from the group (hello) as in:
>
> I am trying to move back task #580..
>
> [host:/dev/cgroup]$ id
> uid=0(root) gid=0(root) groups=0(root)
>
>
> [host:/dev/cgroup]$ echo 580 > tasks
> -bash: echo: write error: Operation not permitted
>
> [host:/dev/cgroup]$ cat hello/tasks
> 580
> 610
> 2104
> [host:/dev/cgroup]$
>
>
> --- On Mon, 12/13/10, Matt Helsley <matthltc at us.ibm.com> wrote:
>
>> From: Matt Helsley <matthltc at us.ibm.com>
>> Subject: Re: cgroup tasks file error
>> To: "Serge E. Hallyn" <serge.hallyn at canonical.com>
>> Cc: "ccmail111" <ccmail111 at yahoo.com>, containers at lists.linux-foundation.org
>> Date: Monday, December 13, 2010, 8:02 PM
>> On Mon, Dec 13, 2010 at 05:16:28PM
>> -0600, Serge E. Hallyn wrote:
>> > Quoting ccmail111 (ccmail111 at yahoo.com):
>> > >
>> > > I see error:[host:/dev/cgroup]$ echo 693 >
>> hello-test/tasks
>> > > -bash: echo: write error: No space left on
>> device
>>
>> This does seem quite odd so I spent a little time looking
>> at this and I agree with Serge.
>>
>> > > [host:/dev/cgroup]$ pwd/dev/cgroup
>> > >
>> > > But the user process is up and running..
>> > >
>> > > [host:/dev/cgroup]$ ps aux | grep procroot
>>
>> > >
>> > > 693  0.0  0.4  34720  1112 ttyS0    Sl
>> 19:11   0:00 /opt/bin/myproc -ext
>> > >
>> > > Also the cgroup exists and valid..
>> > >
>> > > [host:/dev/cgroup]$ ls | grep hello-test
>> > > hello-test
>> > >
>> > > What above error mean and any suggestions ?
>> > > Please email.
>> >
>> > Which cgroups do you have composed on that
>> mount?  I'm guess you
>> > have cpuset, and you need to set the cpuset.mems and
>> cpuset.cpus.
>> > Until you do that, no tasks can be assigned to it.
>>
>> I looked a a few places in kernel/cgroup.c which return
>> ENOSPC
>> or could potentially forward such an error. The only place
>> that
>> fits is in the attach path and is consistent with the
>> notion that
>> it's a cpuset issue:
>>
>> echo <pid> > tasks =>
>> cgroup_tasks_write() =>
>> attach_task_by_pid() =>
>> cgroup_attach_task() => (via ss->can_attach() where
>> ss is the cpuset subsystem)
>> cpuset_can_attach():
>>         if
>> (cpumask_empty(cs->cpus_allowed) ||
>> nodes_empty(cs->mems_allowed))
>>
>> return -ENOSPC;
>>
>> No other cgroup subsystem that I looked at (freezer,
>> memcontrol, ns,
>>     blkio, devcgroup) returns ENOSPC when
>> attaching a task.
>>
>> So not only do you need to set those masks but each mask
>> must have at
>> least one cpu and "mem" respectively.
>>
>> Cheers,
>>     -Matt Helsley
>>
>
>
>
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-- 
Jue Hong (洪爵)
Department of Network Infrastructure
Tencent Company, Shenzhen, China
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