On 7/21/20 5:11 AM, Kirill A. Shutemov wrote:

On Mon, Jul 20, 2020 at 04:51:44PM -0700, Andrew Morton wrote:

quoted

On Sun, 19 Jul 2020 14:10:19 -0700 syzbot [off-list ref] wrote:

quoted

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