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Date: Thu, 28 Jun 2012 09:06:25 -0700
Message-ID: <CAOS58YNuSMjDB00UgOPjGCSFcRx-gjvMrW+e4uW0ug8WMsuFSw@mail.gmail.com>
Subject: Re: [PATCH v3][0/6] memcg: prevent -ENOMEM in pre_destroy()
From: Tejun Heo <tj@kernel.org>
To: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "cgroups@vger.kernel.org" <cgroups@vger.kernel.org>,
        Michal Hocko <mhocko@suse.cz>, Johannes Weiner <hannes@cmpxchg.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Han Ying <yinghan@google.com>, Glauber Costa <glommer@parallels.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Hiroyuki Kamezawa <kamezawa.hiroyuki@gmail.com>,
        Linux Kernel <linux-kernel@vger.kernel.org>
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Hello, KAME.

On Thu, Jun 28, 2012 at 1:33 AM, Kamezawa Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
>> Ooh, once memcg drops the __DEPRECATED_clear_css_refs, cgroup_rmdir()
>> will mark the cgroup dead before start calling pre_destroy() and none
>> of the above will happen.
>>
>
> Hm, threads which touches memcg should hold memcg's reference count rather
> than css.
> Right ? IIUC, one of reason is a reference from kswapd etc...hm. I'll check
> it.

Not sure I'm following. I meant that css_tryget() will always fail
once pre_destroy() calls being for the cgroup, so no new child or
reference can be created for it after that point.

Thanks.

-- 
tejun
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