Re: WARNING: at mm/mremap.c:211 move_page_tables in i386

[Naresh Kamboju <naresh.kamboju@linaro.org>]

On Tue, 14 Jul 2020 at 13:03, Kirill A. Shutemov <kirill@shutemov.name> wrote:
>
> On Sun, Jul 12, 2020 at 03:58:06PM -0700, Linus Torvalds wrote:
> > Anybody else have any opinions?
>
> Maybe we just shouldn't allow move_normal_pmd() if ranges overlap?
>
> Other option: pass 'overlaps' down to move_normal_pmd() and only WARN() if
> see establised PMD without overlaps being true.
>
> Untested patch:

This patch applied on top of Linus mainline tree and tested on i386.
The reported warning did not happen while testing LTP mm [1].


>
> diff --git a/mm/mremap.c b/mm/mremap.c
> index 5dd572d57ca9..e33fcee541fe 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -245,6 +245,18 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
>         unsigned long extent, next, old_end;
>         struct mmu_notifier_range range;
>         pmd_t *old_pmd, *new_pmd;
> +       bool overlaps;
> +
> +       /*
> +        * shift_arg_pages() can call move_page_tables() on overlapping ranges.
> +        * In this case we cannot use move_normal_pmd() because destination pmd
> +        * might be established page table: move_ptes() doesn't free page
> +        * table.
> +        */
> +       if (old_addr > new_addr)
> +               overlaps = old_addr - new_addr < len;
> +       else
> +               overlaps = new_addr - old_addr < len;
>
>         old_end = old_addr + len;
>         flush_cache_range(vma, old_addr, old_end);
> @@ -282,7 +294,7 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
>                         split_huge_pmd(vma, old_pmd, old_addr);
>                         if (pmd_trans_unstable(old_pmd))
>                                 continue;
> -               } else if (extent == PMD_SIZE) {
> +               } else if (!overlaps && extent == PMD_SIZE) {
>  #ifdef CONFIG_HAVE_MOVE_PMD
>                         /*
>                          * If the extent is PMD-sized, try to speed the move by
> --
>  Kirill A. Shutemov

ref:
https://lkft.validation.linaro.org/scheduler/job/1561734#L1598

- Naresh