linux-kernel - Re: WARNING: at mm/mremap.c:211 move_page

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Message-ID: <CAHk-=wgRS_WpRdC9nyXzVZ7aWNQt0HKMbyFjhrgrNo49AFNWzg@mail.gmail.com>
Date:   Tue, 14 Jul 2020 11:49:20 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        linux- stable <stable@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>, Michal Hocko <mhocko@...nel.org>,
        lkft-triage@...ts.linaro.org, Chris Down <chris@...isdown.name>,
        Michel Lespinasse <walken@...gle.com>,
        Fan Yang <Fan_Yang@...u.edu.cn>,
        Brian Geffon <bgeffon@...gle.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>, pugaowei@...il.com,
        Jerome Glisse <jglisse@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Hugh Dickins <hughd@...gle.com>,
        Al Viro <viro@...iv.linux.org.uk>, Tejun Heo <tj@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: WARNING: at mm/mremap.c:211 move_page_tables in i386

On Tue, Jul 14, 2020 at 11:12 AM Joel Fernandes <joel@...lfernandes.org> wrote:
>
> I think you misunderstood me. I was not advocating breaking the stack
> movement code or breaking stack randomization, I was going to try to
> see if I could keep that working while not having to do an overlapping
> move.

I'm not really seeing how you'd do that with a big stack that gets
close to the stack ulimit.

Except by avoiding randomization.

But the existing randomization may be so bad that it doesn't much
matter. And I do think we limit the execve stack to a reasonably small
fraction of the whole ulimit. So worth exploring, I guess.

The current code with "align_stack" doing randomization could also do
with a lot of clarifications. The code is odd.

            Linus