On Thu, Jul 23, 2020 at 03:37:44PM +0800, Hillf Danton wrote: > > On Tue, 21 Jul 2020 14:11:31 +0300 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 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@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > 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()? > > Or is there likely the window that after copy_huge_pmd() the src pmd migrate > entry is removed and the page unlocked but the dst is not? No. copy_huge_pmd() runs with exclusive mmap_lock on the source side and destination side is not running yet. -- Kirill A. Shutemov
