From: Kirill Tkhai <ktkhai@virtuozzo.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>,
Cyrill Gorcunov <gorcunov@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Linux MM <linux-mm@kvack.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>,
Vladimir Davydov <vdavydov.dev@gmail.com>
Subject: Re: [PATCH] mm, memcg: assign shrinker_map before kvfree
Date: Fri, 20 Sep 2019 17:20:14 +0300 [thread overview]
Message-ID: <55c22ce3-5e42-f7a1-3861-8e0cb73d26de@virtuozzo.com> (raw)
In-Reply-To: <20190920132114.ofzphp53vqqjb3fs@box>
On 20.09.2019 16:21, Kirill A. Shutemov wrote:
> On Fri, Sep 20, 2019 at 03:29:07PM +0300, Cyrill Gorcunov wrote:
>> Currently there is a small gap between fetching pointer, calling
>> kvfree and assign its value to nil. In current callgraph it is
>> not a problem (since memcg_free_shrinker_maps is running from
>> memcg_alloc_shrinker_maps and mem_cgroup_css_free only) still
>> this looks suspicious and we can easily eliminate the gap at all.
>
> With this logic it will still look suspicious since you don't wait a grace
> period before freeing the map.
This freeing occurs in the moment, when nobody can dereference shrinker_map
in parallel:
memcg is either not yet online or its css->refcnt is already dead.
This NULLifying is needed just to prevent double freeing of shrinker_map.
Please, see the explanation in my email to our namesake.
Kirill
next prev parent reply other threads:[~2019-09-20 14:20 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-20 12:29 Cyrill Gorcunov
2019-09-20 13:21 ` Kirill A. Shutemov
2019-09-20 13:40 ` Cyrill Gorcunov
2019-09-20 14:20 ` Kirill Tkhai [this message]
2019-09-20 14:11 ` Kirill Tkhai
2019-09-20 14:31 ` Cyrill Gorcunov
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