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SubjectRe: [RFC][PATCH 1/2] CGROUP ID and Hierarchy Code
On Fri, 28 Nov 2008 10:38:26 +0800
Li Zefan <lizf@cn.fujitsu.com> wrote:

> KAMEZAWA Hiroyuki wrote:
> > On Fri, 28 Nov 2008 10:35:33 +0900
> > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> >
> >> On Fri, 28 Nov 2008 09:28:33 +0800
> >> Li Zefan <lizf@cn.fujitsu.com> wrote:
> >
> >>> I think the safe way is:
> >>>
> >>> rcu_read_lock();
> >>> cgrp = cgroup_get_next()
> >>> if (!inc_not_zero(cgrp) {
> >>> rcu_read_unlock();
> >>> return NULL;
> >>> }
> >>> rcu_read_unlock();
> >>> return cgrp;
> >>>
> >>> But it's also safe to use cgrp = list_entry(&parent->children.next) for the above
> >>> scenario, seems you don't have to invent this cgroup_get_next().
> >>>
> >> But list-walk can't provide us view of hierarchy. Up-Down list walk is better ?
> >> please see memcg's code. it met some troubles.
> >> I'll make kfree(cgrp) to be called by RCU.
> >>
> >
> > Ah please, I have a question.
> > Following is right ?
> > - until mount, cgroup's subsystem root is tied to dummy? root cgroup.
>
> Yes.
>
> > - cgroup cannot be unmounted while there are any children.
>
> No, you can unmount. You can have it a try. :)
>
I tried and did ;)

> > - cgroup_root is freed/allocated at umount/mount, then I have to handle
>
> No, kill_sb() is called when deactivate_super() decreases sb->s_active to 0, and
> whenever we create a cgroup, sb->s_active is increased, so if there are sub-dirs
> the cgroup_root won't be freed at umount.
>
Thank you! very helpful.

So, I should take care ofe only kill_sb() case.
(it frees pointer of root (and root->topcgroup.) and I have to update it.)

Regards,
-Kame


> > this event in cgroup-id.
> > (maybe current code has leak? in umount.)
> >
>
> So I think there is no leak. ;)
>
> > Thanks,
> > -Kame
> >
> >
> >
>



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