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

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Message-ID: <20190430105609.GA23779@blackbody.suse.cz>
Date:   Tue, 30 Apr 2019 12:56:10 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Cyrill Gorcunov <gorcunov@...il.com>
Cc:     Kirill Tkhai <ktkhai@...tuozzo.com>, brgl@...ev.pl,
        arunks@...eaurora.org, geert+renesas@...der.be, mhocko@...nel.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org,
        ldufour@...ux.ibm.com, rppt@...ux.ibm.com, mguzik@...hat.com,
        mkoutny@...e.cz, vbabka@...e.cz, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] mm: get_cmdline use arg_lock instead of mmap_sem

On Tue, Apr 30, 2019 at 01:45:17PM +0300, Cyrill Gorcunov <gorcunov@...il.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.

My 2 cents,
Michal

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