From: Michal Hocko <mhocko@suse.cz>
To: Glauber Costa <glommer@parallels.com>
Cc: cgroups@vger.kernel.org, linux-mm@kvack.org,
Tejun Heo <tj@kernel.org>,
kamezawa.hiroyu@jp.fujitsu.com,
Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH 4/4] memcg: replace cgroup_lock with memcg specific memcg_lock
Date: Mon, 3 Dec 2012 18:30:02 +0100 [thread overview]
Message-ID: <20121203173002.GH17093@dhcp22.suse.cz> (raw)
In-Reply-To: <20121203171532.GG17093@dhcp22.suse.cz>
On Mon 03-12-12 18:15:32, Michal Hocko wrote:
[...]
> > @@ -3915,7 +3926,7 @@ static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft,
> > */
> > if ((!parent_memcg || !parent_memcg->use_hierarchy) &&
> > (val == 1 || val == 0)) {
> > - if (list_empty(&cont->children))
> > + if (!memcg_has_children(memcg))
> > memcg->use_hierarchy = val;
> > else
> > retval = -EBUSY;
>
> Nothing prevents from a race when a task is on the way to be attached to
> the group. This means that we might miss some charges up the way to the
> parent.
>
> mem_cgroup_hierarchy_write
> cgroup_attach_task
> ss->can_attach() = mem_cgroup_can_attach
> mutex_lock(&memcg_lock)
> memcg->attach_in_progress++
> mutex_unlock(&memcg_lock)
> __mem_cgroup_can_attach
> mem_cgroup_precharge_mc (*)
> mutex_lock(memcg_lock)
> memcg_has_children(memcg)==false
Dohh, retard alert. I obviously mixed tasks and children cgroups here.
Why I thought we also do check for no tasks in the group? Ahh, because
we should, at least here otherwise parent could see more uncharges than
charges.
But that deserves a separate patch. Sorry, for the confusion.
> cgroup_task_migrate
> memcg->use_hierarchy = val;
> ss->attach()
>
> (*) All the charches here are not propagated upwards.
>
> Fixable simply by testing attach_in_progress as well. The same applies
> to all other cases so it would be much better to prepare a common helper
> which does the whole magic.
>
> [...]
>
> Thanks
> --
> Michal Hocko
> SUSE Labs
> --
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--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2012-12-03 17:30 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-30 13:31 [PATCH 0/4] replace cgroup_lock with local lock in memcg Glauber Costa
2012-11-30 13:31 ` [PATCH 1/4] cgroup: warn about broken hierarchies only after css_online Glauber Costa
2012-11-30 15:11 ` Tejun Heo
2012-11-30 15:13 ` Glauber Costa
2012-11-30 15:45 ` Tejun Heo
2012-11-30 15:49 ` Michal Hocko
2012-11-30 15:57 ` Glauber Costa
2012-11-30 13:31 ` [PATCH 2/4] memcg: prevent changes to move_charge_at_immigrate during task attach Glauber Costa
2012-11-30 15:19 ` Tejun Heo
2012-11-30 15:29 ` Glauber Costa
2012-12-04 9:29 ` Michal Hocko
2012-11-30 13:31 ` [PATCH 3/4] memcg: split part of memcg creation to css_online Glauber Costa
2012-12-03 17:32 ` Michal Hocko
2012-12-04 8:05 ` Glauber Costa
2012-12-04 8:17 ` Michal Hocko
2012-12-04 8:32 ` Glauber Costa
2012-12-04 8:52 ` Michal Hocko
2012-11-30 13:31 ` [PATCH 4/4] memcg: replace cgroup_lock with memcg specific memcg_lock Glauber Costa
2012-12-03 17:15 ` Michal Hocko
2012-12-03 17:30 ` Michal Hocko [this message]
2012-12-04 7:49 ` Glauber Costa
2012-12-04 7:58 ` Glauber Costa
2012-12-04 8:23 ` Michal Hocko
2012-12-04 8:31 ` Glauber Costa
2012-12-04 8:45 ` Michal Hocko
2012-12-04 14:52 ` Tejun Heo
2012-12-04 15:14 ` Michal Hocko
2012-12-04 15:22 ` Tejun Heo
2012-12-05 14:35 ` Michal Hocko
2012-12-05 14:41 ` Tejun Heo
2012-11-30 15:52 ` [PATCH 0/4] replace cgroup_lock with local lock in memcg Tejun Heo
2012-11-30 15:59 ` Glauber Costa
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