linux-kernel - Re: [mm] f886cdb769: kernel_BUG_at

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Date:   Fri, 18 Mar 2022 00:50:58 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     kernel test robot <oliver.sang@...el.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Alistair Popple <apopple@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Hugh Dickins <hughd@...gle.com>, Jan Kara <jack@...e.cz>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Ralph Campbell <rcampbell@...dia.com>,
        Ross Zwisler <zwisler@...nel.org>,
        Xiongchun Duan <duanxiongchun@...edance.com>,
        Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Yang Shi <shy828301@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
        kernel test robot <lkp@...el.com>
Subject: Re: [mm] f886cdb769: kernel_BUG_at_include/linux/swapops.h

On Thu, Mar 17, 2022 at 4:05 PM kernel test robot <oliver.sang@...el.com> wrote:
>
>
>
> Greeting,
>
> FYI, we noticed the following commit (built with gcc-9):
>
> commit: f886cdb76920131b030ffae13e752d8d0ff440f0 ("mm: pvmw: add support for walking devmap pages")
> url: https://github.com/0day-ci/linux/commits/Petr-Mladek/kthread-Make-it-clear-that-kthread_create_on_node-might-be-terminated-by-any-fatal-signal/20220315-182614
>
> in testcase: will-it-scale
> version: will-it-scale-x86_64-a34a85c-1_20220312
> with following parameters:
>
>         nr_task: 100%
>         mode: process
>         test: lock1
>         cpufreq_governor: performance
>         ucode: 0x2006c0a
>
> test-description: Will It Scale takes a testcase and runs it from 1 through to n parallel copies to see if the testcase will scale. It builds both a process and threads based test in order to see any differences between the two.
> test-url: https://github.com/antonblanchard/will-it-scale
>
>
> on test machine: 104 threads 2 sockets Skylake with 192G memory
>
> caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
>
>
>
> If you fix the issue, kindly add following tag
> Reported-by: kernel test robot <oliver.sang@...el.com>
>
>

Thanks for your report. I knew the reason. Because pmd_devmap() is
only reliable when pmd_present() returns true and  pmd_devmap() could
returns tue for pmd swap entry.  I should test pmd_present() before
pmd_devmap().  Will be fixed in the next version.

Thanks.