linux-kernel - Re: [PATCH 1/3] mm: get_cmdline use arg_lock instead of mmap

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Message-ID: <20190430104517.GF2673@uranus.lan>
Date:   Tue, 30 Apr 2019 13:45:17 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     Michal Koutný <mkoutny@...e.com>,
        akpm@...ux-foundation.org, arunks@...eaurora.org, brgl@...ev.pl,
        geert+renesas@...der.be, ldufour@...ux.ibm.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        mguzik@...hat.com, mhocko@...nel.org, rppt@...ux.ibm.com,
        vbabka@...e.cz
Subject: Re: [PATCH 1/3] mm: get_cmdline use arg_lock instead of mmap_sem

On Tue, Apr 30, 2019 at 12:53:51PM +0300, Kirill Tkhai wrote:
> > 
> > Well, strictly speaking we probably should but you know setup of
> > the @arg_start by kernel's elf loader doesn't cause any side
> > effects as far as I can tell (its been working this lockless
> > way for years, mmap_sem is taken later in the loader code).
> > Though for consistency sake we probably should set it up
> > under the spinlock.
> 
> Ok, so elf loader doesn't change these parameters.
> Thanks for the explanation.

It setups these parameters unconditionally. I need to revisit
this moment. Technically (if only I'm not missing something
obvious) we might have a race here with prctl setting up new
params, but this should be harmless since most of them (except
stack setup) are purely informative data.