linux-kernel - Re: [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm

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Message-ID: <0bfa8943-a2fe-b0ab-99a2-347094a2bcec@i-love.sakura.ne.jp>
Date:   Tue, 27 Mar 2018 06:10:09 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Cyrill Gorcunov <gorcunov@...il.com>,
        Matthew Wilcox <willy@...radead.org>
Cc:     Yang Shi <yang.shi@...ux.alibaba.com>, adobriyan@...il.com,
        mhocko@...nel.org, mguzik@...hat.com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and
 env_start|end in mm_struct

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?