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Date:   Tue, 30 Apr 2019 16:24:03 +0300
From:   Cyrill Gorcunov <gorcunov@gmail.com>
To:     Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>
Cc:     Kirill Tkhai <ktkhai@virtuozzo.com>, brgl@bgdev.pl,
        arunks@codeaurora.org, geert+renesas@glider.be, mhocko@kernel.org,
        linux-mm@kvack.org, akpm@linux-foundation.org,
        ldufour@linux.ibm.com, rppt@linux.ibm.com, mguzik@redhat.com,
        mkoutny@suse.cz, vbabka@suse.cz, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] mm: get_cmdline use arg_lock instead of mmap_sem
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On Tue, Apr 30, 2019 at 12:56:10PM +0200, Michal Koutn? wrote:
> On Tue, Apr 30, 2019 at 01:45:17PM +0300, Cyrill Gorcunov <gorcunov@gmail.com> wrote:
> > 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.
>
> FTR, when I reviewed that usage, I noticed it was missing the
> synchronization. My understanding was that the mm_struct isn't yet
> shared at this moment. I can see some of the operations take place after
> flush_old_exec (where current->mm = mm_struct), so potentially it is
> shared since then. OTOH, I guess there aren't concurrent parties that
> could access the field at this stage of exec.

Just revisited this code -- we're either executing prctl, either execve.
Since both operates with current task we're safe.