linux-kernel - Re: kernel BUG at include/linux/swapops.h:LINE!

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Message-ID: <16e40194-05ac-536b-303f-d2fd31493229@kernel.dk>
Date:   Tue, 21 Jul 2020 09:11:41 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     syzbot <syzbot+c48f34012b06c4ac67dd@...kaller.appspotmail.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        syzkaller-bugs@...glegroups.com,
        Matthew Wilcox <willy@...radead.org>,
        Ralph Campbell <rcampbell@...dia.com>,
        David Hildenbrand <david@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: kernel BUG at include/linux/swapops.h:LINE!

On 7/21/20 5:11 AM, Kirill A. Shutemov wrote:
> On Mon, Jul 20, 2020 at 04:51:44PM -0700, Andrew Morton wrote:
>> On Sun, 19 Jul 2020 14:10:19 -0700 syzbot <syzbot+c48f34012b06c4ac67dd@...kaller.appspotmail.com> wrote:
>>
>>> syzbot has found a reproducer for the following issue on:
>>>
>>> HEAD commit:    4c43049f Add linux-next specific files for 20200716
>>> git tree:       linux-next
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=12c56087100000
>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=2c76d72659687242
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=c48f34012b06c4ac67dd
>>> compiler:       gcc (GCC) 10.1.0-syz 20200507
>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1344abeb100000
>>>
>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>>> Reported-by: syzbot+c48f34012b06c4ac67dd@...kaller.appspotmail.com
>>
>> Thanks.
>>
>> __handle_mm_fault
>>   ->pmd_migration_entry_wait
>>     ->migration_entry_to_page
>>
>> stumbled onto an unlocked page.
>>
>> I don't immediately see a cause.  Perhaps Matthew's "THP prep patches",
>> perhaps something else.
>>
>> Is it possible to perform a bisection?
> 
> Maybe it's related to the new lock_page_async()?

Shouldn't be used for any of those paths at all, though of course can't
rule out a bug that triggers it somehow. A bisection would be nice.


-- 
Jens Axboe