Re: [PATCH 2/3] cgroups: add inactive subsystems to rootnode.root_list

[Li Zefan <lizf@cn.fujitsu.com>]

>>>> @@ -2522,6 +2522,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
>>>>        printk(KERN_INFO "Initializing cgroup subsys %s\n", ss->name);
>>>>
>>>>        /* Create the top cgroup state for this subsystem */
>>>> +       list_add(&ss->sibling, &rootnode.root_list);
>>> This is wrong. cgroup_subsys.sibling is a member of the list of
>>> subsystems attached to a given root, and rootnode.root_list is a
>>> member of the list of hierarchies. Did you actually meant
>>> &rootnode.subsys_list?
>>>
>> I thought I corrected all the s/root_list/subsys_list/ in patch v2. :(
>>
>> If this patch makes sense, I'll fix it, otherwise we'll going to ask Andrew to drop it from -mm.
> 
> Looking at the existing code, it's not actually broken - but only by accident.
> 

Yes, since it's not broken, I didn't claim this patch as a bug fix that
should go into 2.6.28.

> We aim to add a link for each cgroup, which we do by finding the first
> subsystem in each hierarchy and adding a link for its cgroup, and then
> adding a link for dummytop if there weren't any subsystems in the
> inactive hierarchy.
> 
> But since rootnode.subsys_list is always empty, we always skip the
> inactive hierarchy in the main loop (if it has any subsystems), and
> always add the inactive hierarchy afterwards. So everything works out
> OK (all hierarchies do get linked), but it's horribly unreadable.
> 

I found this confusion when I was trying to understand this part of code.

> Having the subsys_list be correct for the inactive hierarchy is
> probably a good thing, so this patch should go ahead (once the typos
> is fixed).
> 

I'll fix it. :)