linux-kernel - Re: [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm

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Message-ID: <20180328131042.GL9275@dhcp22.suse.cz>
Date:   Wed, 28 Mar 2018 15:10:42 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Cyrill Gorcunov <gorcunov@...il.com>
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: [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and
 env_start|end in mm_struct

On Tue 27-03-18 21:52:17, Cyrill Gorcunov wrote:
> 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).

Ohh, it would be really great if we can remove this thingy altogether. I
cannot say it has a wee bit of my sympathy.

-- 
Michal Hocko
SUSE Labs