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

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Message-ID: <CAEXW_YRTnCb-z6TeboA3OCYv8eoX8UiCNn7K1hGMX+41Zdz8Og@mail.gmail.com>
Date:   Tue, 14 Jul 2020 14:12:33 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Linus Torvalds <torvalds@...ux-foundation.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 12:11 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Tue, Jul 14, 2020 at 9:08 AM Joel Fernandes <joel@...lfernandes.org> wrote:
> >
> > I was thinking we should not call move_page_tables() with overlapping ranges
> > at all, just to keep things simple.
>
> No, we're not breaking the existing stack movement code just to keep
> things simple.
>
> The rule is "make it as simple as possible, but no simpler".
>
> And "as possible" in the case of Linux means "no breaking of old
> interfaces". The stack randomization movement most certainly counts.

Hi Linus,
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. That would be what I would do in the future patch (until which
as you mentioned, you would switch the WARN_ON to WARN_ON_ONCE).

I agree with you that we keep things as simple as possible while not
breaking functionality.

Cheers,

 - Joel