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Date:   Tue, 27 Mar 2018 21:52:17 +0300
From:   Cyrill Gorcunov <gorcunov@gmail.com>
To:     Yang Shi <yang.shi@linux.alibaba.com>
Cc:     Michal Hocko <mhocko@kernel.org>, adobriyan@gmail.com,
        willy@infradead.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
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On Tue, Mar 27, 2018 at 02:38:11PM -0400, Yang Shi wrote:
> > Why do we need to hold mmap_sem here and call find_vma, when only
> > PR_SET_MM_ENV_END: is consuming it? I guess we can replace it wit the
> > new lock and take the mmap_sem only for PR_SET_MM_ENV_END.
> 
> Actually, I didn't think of why. It looks prctl_set_mm() checks if vma does
> exist when it tries to set stack_start, argv_* and env_*, btw not only
> env_end.
> 
> Cyrill may be able to give us some hint since C/R is the main user of this
> API.

First and most important it makes code smaller. This prctl call is really
rarely used. Of course we can optimize it, but as I said I would prefer
to simply deprecate this old interface (and I gonne to do so once time
permit).