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Subject: Re: kernel BUG at include/linux/swapops.h:LINE!
To:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     syzbot <syzbot+c48f34012b06c4ac67dd@syzkaller.appspotmail.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        syzkaller-bugs@googlegroups.com,
        Matthew Wilcox <willy@infradead.org>,
        Ralph Campbell <rcampbell@nvidia.com>,
        David Hildenbrand <david@redhat.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Johannes Weiner <hannes@cmpxchg.org>
References: <000000000000bc4fd705a6e090e2@google.com>
 <0000000000004c38cd05aad1d13f@google.com>
 <20200720165144.93189f7825bd28e234a42cb8@linux-foundation.org>
 <20200721111131.bo3g6qkcvbhpupon@black.fi.intel.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <16e40194-05ac-536b-303f-d2fd31493229@kernel.dk>
Date:   Tue, 21 Jul 2020 09:11:41 -0600
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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@syzkaller.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@syzkaller.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