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

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Date:   Fri, 10 Jul 2020 13:05:26 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Naresh Kamboju <naresh.kamboju@...aro.org>
Cc:     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>,
        Joel Fernandes <joel@...lfernandes.org>,
        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 Fri, Jul 10, 2020 at 10:48 AM Naresh Kamboju
<naresh.kamboju@...aro.org> wrote:
>
> I have applied your patch and test started in a loop for a million times
> but the test ran for 35 times. Seems like the test got a timeout after 1 hour.

That just means that my test-case was wrong (in the sense that what it
was testing wasn't what was triggering things).

It might be wrong because I got the stack usage calculations wrong,
but it might be wrong simply because the bug you've triggered with LTP
needs something else to trigger.

> Re-running test with long timeouts 4 hours and will share findings.

That test was more intended to trigger the issue reliably, if it was
just a "stack is special, needs that exact 2MB aligned case to be
problematic".

So re-running my "t.c" the test for long times with that kernel patch
that removes the stack randomization isn't going to matter. Either it
triggers the case, or not.

I don't actually see any case where we play with vm_start the way we
used to (it was basically removed with commit 1be7107fbe18: "mm:
larger stack guard gap, between vmas"). So it was kind of a log shot
anyway.

              Linus