From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Subject: hugetlb: fix nr_pmds accounting with shared page tables We account HugeTLB's shared page table to all processes who share it. The accounting happens during huge_pmd_share(). If somebody populates pud entry under us, we should decrease pagetable's refcount and decrease nr_pmds of the process. By mistake, I increase nr_pmds again in this case. :-/ It will lead to "BUG: non-zero nr_pmds on freeing mm: 2" on process' exit. Let's fix this by increasing nr_pmds only when we're sure that the page table will be used. Link: http://lkml.kernel.org/r/20160617122506.GC6534@xxxxxxxxxxxxxxxxxx Fixes: dc6c9a35b66b ("mm: account pmd page tables to the process") Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Reported-by: zhongjiang <zhongjiang@xxxxxxxxxx> Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/hugetlb.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff -puN mm/hugetlb.c~hugetlb-fix-nr_pmds-accounting-with-shared-page-tables mm/hugetlb.c --- a/mm/hugetlb.c~hugetlb-fix-nr_pmds-accounting-with-shared-page-tables +++ a/mm/hugetlb.c @@ -4228,7 +4228,6 @@ pte_t *huge_pmd_share(struct mm_struct * if (saddr) { spte = huge_pte_offset(svma->vm_mm, saddr); if (spte) { - mm_inc_nr_pmds(mm); get_page(virt_to_page(spte)); break; } @@ -4243,9 +4242,9 @@ pte_t *huge_pmd_share(struct mm_struct * if (pud_none(*pud)) { pud_populate(mm, pud, (pmd_t *)((unsigned long)spte & PAGE_MASK)); + mm_inc_nr_pmds(mm); } else { put_page(virt_to_page(spte)); - mm_inc_nr_pmds(mm); } spin_unlock(ptl); out: _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
