[BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM)

Martin Schwidefsky
2016-02-24T08:39:15Z

On Tue, 23 Feb 2016 22:33:45 +0300
"Kirill A. Shutemov" <kirill@shutemov.name> wrote:

> On Tue, Feb 23, 2016 at 07:19:07PM +0100, Gerald Schaefer wrote:
> > I'll check with Martin, maybe it is actually trivial, then we can
> > do a quick test it to rule that one out.
>
> Oh. I found a bug in __split_huge_pmd_locked(). Although, not sure if it's
> _the_ bug.
>
> pmdp_invalidate() is called for the wrong address :-/
> I guess that can be destructive on the architecture, right?
>
> Could you check this?
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 1c317b85ea7d..4246bc70e55a 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2865,7 +2865,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> pgtable = pgtable_trans_huge_withdraw(mm, pmd);
> pmd_populate(mm, &_pmd, pgtable);
>
> - for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
> + for (i = 0; i < HPAGE_PMD_NR; i++) {
> pte_t entry, *pte;
> /*
> * Note that NUMA hinting access restrictions are not
> @@ -2886,9 +2886,9 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> }
> if (dirty)
> SetPageDirty(page + i);
> - pte = pte_offset_map(&_pmd, haddr);
> + pte = pte_offset_map(&_pmd, haddr + i * PAGE_SIZE);
> BUG_ON(!pte_none(*pte));
> - set_pte_at(mm, haddr, pte, entry);
> + set_pte_at(mm, haddr + i * PAGE_SIZE, pte, entry);
> atomic_inc(&page[i]._mapcount);
> pte_unmap(pte);
> }
> @@ -2938,7 +2938,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> pmd_populate(mm, pmd, pgtable);
>
> if (freeze) {
> - for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
> + for (i = 0; i < HPAGE_PMD_NR; i++) {
> page_remove_rmap(page + i, false);
> put_page(page + i);
> }

Test is running and it looks good so far. For the final assessment I defer
to Gerald and Sebastian.

--
blue skies,
Martin.

"Reality continues to ruin my life." - Calvin.