From: Kirill A. Shutemov Date: Fri, 24 Jun 2016 21:49:51 +0000 (-0700) Subject: hugetlb: fix nr_pmds accounting with shared page tables X-Git-Tag: v4.7-rc5~11^2~13 X-Git-Url: http://git.cascardo.eti.br/?p=cascardo%2Flinux.git;a=commitdiff_plain;h=c17b1f42594eb71b8d3eb5a6dfc907a7eb88a51d 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@node.shutemov.name Fixes: dc6c9a35b66b ("mm: account pmd page tables to the process") Signed-off-by: Kirill A. Shutemov Reported-by: zhongjiang Reviewed-by: Mike Kravetz Acked-by: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 388c2bb9b55c..ee0302169959 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4228,7 +4228,6 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud) 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 *mm, unsigned long addr, pud_t *pud) 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: