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

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Date:   Thu, 9 Jul 2020 10:25:31 +0200
From:   Arnd Bergmann <arnd@...db.de>
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>,
        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>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Michel Lespinasse <walken@...gle.com>, Fan_Yang@...u.edu.cn,
        bgeffon@...gle.com, Anshuman Khandual <anshuman.khandual@....com>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>, pugaowei@...il.com,
        Jérôme 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 Thu, Jul 9, 2020 at 7:28 AM Naresh Kamboju <naresh.kamboju@...aro.org> wrote:
>
> While running LTP mm test suite on i386 or qemu_i386 this kernel warning
> has been noticed from stable 5.4 to stable 5.7 branches and mainline 5.8.0-rc4
> and linux next.

Are you able to correlate this with any particular test case in LTP, or does
it happen for random processes?

In the log you linked to, it happens once for ksm05.c and multiple times for
thp01.c, sources here:

https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/mem/ksm/ksm05.c
https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/mem/thp/thp01.c

Is it always these tests that trigger the warning, or sometimes others?

When you say it happens with linux-5.4 stable, does that mean you don't see
it with older versions? What is the last known working version?

I also see that you give the virtual machine 16GB of RAM, but as you are
running a 32-bit kernel without PAE, only 2.3GB end up being available,
and some other LTP tests in the log run out of memory.

You could check if the behavior changes if you give the kernel less memory,
e.g. 768MB (lowmem only), or enable CONFIG_X86_PAE to let it use the
entire 16GB.

> full test log,
> https://lkft.validation.linaro.org/scheduler/job/1541788#L9308

       Arnd