linux-kernel - Re: [PATCH 0/1] expand_downwards: don't require the gap if !vm

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Message-ID: <CA+55aFwaOBdp-ETuLxh=uxTjjGB5VKAh3ST=O0Se8R5NMumCwA@mail.gmail.com>
Date:   Fri, 30 Jun 2017 10:48:15 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Oleg Nesterov <oleg@...hat.com>, Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Larry Woodman <lwoodman@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/1] expand_downwards: don't require the gap if !vm_prev

On Fri, Jun 30, 2017 at 10:26 AM, Michal Hocko <mhocko@...nel.org> wrote:
>
> Ohh, you misunderstood I guess. They wanted that only for internal
> testing (e.g. make sure that everything that matters blows up if it is
> doing something wrong). Absolutely nothing to base any compilator
> decistion on.

Oh, good.

If that's the case, I really think we should try to add some code that
checks that the stack grows strictly one page at a time, and have a
way to enable SIGSEGV if that is ever not the case.

That should be trivial to add in expand_downwards/expand_upwards.

We could make a "warn once" thing unconditional for distro testing,
but since compiler people would presumably want to test this before
the rest of the distro is clean, they'd need some rlimit or something
like that to enable it for particular processes.

Would that be ok for them?

Some prctl to get/set that "max I'm allowed to extend the stack"?

                Linus