From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Matthew Wilcox <willy@infradead.org>,
Yang Shi <yang.shi@linux.alibaba.com>,
adobriyan@gmail.com, mhocko@kernel.org, mguzik@redhat.com,
akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct
Date: Tue, 27 Mar 2018 00:29:44 +0300 [thread overview]
Message-ID: <20180326212944.GF2236@uranus> (raw)
In-Reply-To: <0bfa8943-a2fe-b0ab-99a2-347094a2bcec@i-love.sakura.ne.jp>
On Tue, Mar 27, 2018 at 06:10:09AM +0900, 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);
>
True, but the key moment is that two/three/four system calls can
run simultaneously. And while previously they are ordered by "write",
with read lock they are completely unordered and this is really
worries me. To be fair I would prefer to drop this old per-field
interface completely. This per-field interface was rather an ugly
solution from my side.
> 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?
Tetsuo, let me re-read this code tomorrow, maybe I miss something obvious.
next prev parent reply other threads:[~2018-03-26 21:29 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-26 18:20 [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct Yang Shi
2018-03-26 18:37 ` Matthew Wilcox
2018-03-26 19:21 ` Cyrill Gorcunov
2018-03-26 21:10 ` Tetsuo Handa
2018-03-26 21:20 ` Yang Shi
2018-03-26 21:29 ` Cyrill Gorcunov [this message]
2018-03-26 22:00 ` Tetsuo Handa
2018-03-26 22:12 ` Yang Shi
2018-03-27 7:38 ` Cyrill Gorcunov
2018-03-27 7:37 ` Cyrill Gorcunov
2018-03-26 21:59 ` Yang Shi
2018-03-27 7:32 ` Cyrill Gorcunov
2018-03-27 18:44 ` Yang Shi
2018-03-26 19:42 ` Mateusz Guzik
2018-03-26 21:10 ` Yang Shi
2018-03-27 6:29 ` Michal Hocko
2018-03-27 14:31 ` Mateusz Guzik
2018-03-27 14:43 ` Michal Hocko
2018-03-27 18:38 ` Yang Shi
2018-03-27 18:52 ` Cyrill Gorcunov
2018-03-28 13:10 ` Michal Hocko
2018-04-02 1:58 ` Yang Shi
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