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    SubjectRe: [RFC][PATCH 1/2] CGROUP ID and Hierarchy Code
    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.
    - cgroup cannot be unmounted while there are any children.
    - cgroup_root is freed/allocated at umount/mount, then I have to handle
    this event in cgroup-id.
    (maybe current code has leak? in umount.)

    Thanks,
    -Kame



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