On Fri, Jul 17, 2020 at 03:40:04PM -0700, syzbot wrote: > syzbot has bisected this issue to: > > commit ffe945e633b527d5a4577b42cbadec3c7cbcf096 > Author: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > Date: Wed Jun 3 23:00:09 2020 +0000 > > khugepaged: do not stop collapse if less than half PTEs are referenced > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=17356c2f100000 > start commit: e44f65fd xen-netfront: remove redundant assignment to vari.. > git tree: net-next > final oops: https://syzkaller.appspot.com/x/report.txt?x=14b56c2f100000 > console output: https://syzkaller.appspot.com/x/log.txt?x=10b56c2f100000 > kernel config: https://syzkaller.appspot.com/x/.config?x=829871134ca5e230 > dashboard link: https://syzkaller.appspot.com/bug?extid=ed318e8b790ca72c5ad0 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=113406a7100000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=175597d3100000 > > Reported-by: syzbot+ed318e8b790ca72c5ad0@xxxxxxxxxxxxxxxxxxxxxxxxx > Fixes: ffe945e633b5 ("khugepaged: do not stop collapse if less than half PTEs are referenced") > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection > My guess is that anonymous VMA got replaced by file VMA under us. Could you reproduce the issue with the patch below? I have hard time triggering it myself. diff --git a/mm/khugepaged.c b/mm/khugepaged.c index b043c40a21d4..f8ec58a1e72b 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1107,6 +1107,8 @@ static void collapse_huge_page(struct mm_struct *mm, if (mm_find_pmd(mm, address) != pmd) goto out; + if (!vma->anon_vma) + dump_vma(vma); anon_vma_lock_write(vma->anon_vma); mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm, -- Kirill A. Shutemov
