Commit c17b1f42 authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Linus Torvalds

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: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: default avatarzhongjiang <zhongjiang@huawei.com>
Reviewed-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 06d8fbc7
...@@ -4228,7 +4228,6 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud) ...@@ -4228,7 +4228,6 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)
if (saddr) { if (saddr) {
spte = huge_pte_offset(svma->vm_mm, saddr); spte = huge_pte_offset(svma->vm_mm, saddr);
if (spte) { if (spte) {
mm_inc_nr_pmds(mm);
get_page(virt_to_page(spte)); get_page(virt_to_page(spte));
break; break;
} }
...@@ -4243,9 +4242,9 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud) ...@@ -4243,9 +4242,9 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)
if (pud_none(*pud)) { if (pud_none(*pud)) {
pud_populate(mm, pud, pud_populate(mm, pud,
(pmd_t *)((unsigned long)spte & PAGE_MASK)); (pmd_t *)((unsigned long)spte & PAGE_MASK));
mm_inc_nr_pmds(mm);
} else { } else {
put_page(virt_to_page(spte)); put_page(virt_to_page(spte));
mm_inc_nr_pmds(mm);
} }
spin_unlock(ptl); spin_unlock(ptl);
out: out:
......
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