linux-kernel - Re: [PATCH 1/8] cgroup: implement cgroup_is

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 9 Apr 2013 08:42:49 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Tejun Heo <tj@...nel.org>
Cc:	Li Zefan <lizefan@...wei.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Glauber Costa <glommer@...allels.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH 1/8] cgroup: implement cgroup_is_ancestor()

On Mon 08-04-13 14:36:46, Tejun Heo wrote:
> On Mon, Apr 08, 2013 at 08:03:44PM +0200, Michal Hocko wrote:
> > __mem_cgroup_same_or_subtree relies on css_is_ancestor if hierarchy is
> > enabled for ages. This, however, is not correct because use_hierarchy
> > doesn't need to be true all the way up the cgroup hierarchy. Consider
> > the following example:
> > root (use_hierarchy=0)
> >  \
> >   A (use_hierarchy=0)
> >    \
> >     B (use_hierarchy=1)
> >      \
> >       C (use_hierarchy=1)
> > 
> > __mem_cgroup_same_or_subtree(A, C) would return true even though C is
> > not from the same hierarchy subtree. The bug shouldn't be critical but
> > at least dump_tasks might print unrelated tasks (via
> > task_in_mem_cgroup).
> 
> Huh?  Isn't that avoided by the !root_memcg->use_hierarchy test?

Yes, it is. My selective blindness strikes again :/ I was convinced that
it was memcg we tested use_hierarchy for...
Sorry about all the churn.

> > @@ -1470,9 +1470,12 @@ bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
> >  {
> >  	if (root_memcg == memcg)
> >  		return true;
> > -	if (!root_memcg->use_hierarchy || !memcg)
>             ^^^^^^^^^^^^^^^^^^^^^^^^^^
> > +	if (!memcg)
> >  		return false;
> > -	return css_is_ancestor(&memcg->css, &root_memcg->css);
> > +	while ((memcg = parent_mem_cgroup(memcg)))
> > +		if (memcg == root_memcg)
> > +			return true;
> > +	return false;
> >  }
> >  
-- 
Michal Hocko
SUSE Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/