Commit c17b1f42 authored Jun 24, 2016 by Kirill A. Shutemov Committed by Linus Torvalds Jun 24, 2016

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: dc6c9a35 ("mm: account pmd page tables to the process")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: zhongjiang <zhongjiang@huawei.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 06d8fbc7

mm/hugetlb.c

+1 −2

Original line number	Diff line number	Diff line
		@@ -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: