linux-kernel - Re: [v3 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm

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Message-ID: <20180410122804.GD2041@uranus.lan>
Date:   Tue, 10 Apr 2018 15:28:04 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Yang Shi <yang.shi@...ux.alibaba.com>, adobriyan@...il.com,
        willy@...radead.org, mguzik@...hat.com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [v3 PATCH] mm: introduce arg_lock to protect arg_start|end and
 env_start|end in mm_struct

On Tue, Apr 10, 2018 at 01:10:01PM +0200, Michal Hocko wrote:
> > 
> > Because do_brk does vma manipulations, for this reason it's
> > running under down_write_killable(&mm->mmap_sem). Or you
> > mean something else?
> 
> Yes, all we need the new lock for is to get a consistent view on brk
> values. I am simply asking whether there is something fundamentally
> wrong by doing the update inside the new lock while keeping the original
> mmap_sem locking in the brk path. That would allow us to drop the
> mmap_sem lock in the proc path when looking at brk values.

Michal gimme some time. I guess  we might do so, but I need some
spare time to take more precise look into the code, hopefully today
evening. Also I've a suspicion that we've wracked check_data_rlimit
with this new lock in prctl. Need to verify it again.