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Subject: Re: [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and
 env_start|end in mm_struct
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Matthew Wilcox <willy@infradead.org>
Cc:     adobriyan@gmail.com, mhocko@kernel.org, mguzik@redhat.com,
        akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
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From:   Yang Shi <yang.shi@linux.alibaba.com>
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Date:   Mon, 26 Mar 2018 17:20:33 -0400
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On 3/26/18 5:10 PM, Tetsuo Handa wrote:
> On 2018/03/27 4:21, Cyrill Gorcunov wrote:
>> That said I think using read-lock here would be a bug.
> If I understand correctly, the caller can't set both fields atomically, for
> prctl() does not receive both fields at one call.
>
>    prctl(PR_SET_MM, PR_SET_MM_ARG_START xor PR_SET_MM_ARG_END xor PR_SET_MM_ENV_START xor PR_SET_MM_ENV_END, new value, 0, 0);
>
> Then, I wonder whether reading arg_start|end and env_start|end atomically makes
> sense. Just retry reading if arg_start > env_end or env_start > env_end is fine?

It might trap into dead loop if those are set to wrong values, right?