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References: <20190822062210.18649-1-yzhai003@ucr.edu> <20190822070550.GA12785@dhcp22.suse.cz>
 <CABvMjLRCt4gC3GKzBehGppxfyMOb6OGQwW-6Yu_+MbMp5tN3tg@mail.gmail.com> <20190822201200.GP12785@dhcp22.suse.cz>
In-Reply-To: <20190822201200.GP12785@dhcp22.suse.cz>
From:   Yizhuo Zhai <yzhai003@ucr.edu>
Date:   Fri, 30 Aug 2019 15:27:50 -0700
Message-ID: <CABvMjLRFm5ghgXJYuuNOOSzg01EgE1MazAY7c6HXZaa6wogF8g@mail.gmail.com>
Subject: Re: [PATCH] mm/memcg: return value of the function
 mem_cgroup_from_css() is not checked
To:     Michal Hocko <mhocko@kernel.org>
Cc:     Chengyu Song <csong@cs.ucr.edu>, Zhiyun Qian <zhiyunq@cs.ucr.edu>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        cgroups@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
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Sender: linux-kernel-owner@vger.kernel.org
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Our tool did not trace back the whole path, so, now we could say it
might happen.

On Thu, Aug 22, 2019 at 1:12 PM Michal Hocko <mhocko@kernel.org> wrote:
>
> On Thu 22-08-19 13:07:17, Yizhuo Zhai wrote:
> > This will happen if variable "wb->memcg_css" is NULL. This case is reported
> > by our analysis tool.
>
> Does your tool report the particular call path and conditions when that
> happen? Or is it just a "it mignt happen" kinda thing?
>
> > Since the function mem_cgroup_wb_domain() is visible to the global, we
> > cannot control caller's behavior.
>
> I am sorry but I do not understand what is this supposed to mean.
> --
> Michal Hocko
> SUSE Labs


-- 
Kind Regards,

Yizhuo Zhai

Computer Science, Graduate Student
University of California, Riverside