4.4-stable review patch. If anyone has any objections, please let me know.
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From: Kirill A. Shutemov kirill.shutemov@linux.intel.com
commit a8f97366452ed491d13cf1e44241bc0b5740b1f0 upstream.
Currently, we unconditionally make page table dirty in touch_pmd(). It may result in false-positive can_follow_write_pmd().
We may avoid the situation, if we would only make the page table entry dirty if caller asks for write access -- FOLL_WRITE.
The patch also changes touch_pud() in the same way.
Signed-off-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Michal Hocko mhocko@suse.com Cc: Hugh Dickins hughd@google.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org [Salvatore Bonaccorso: backport for 3.16: - Adjust context - Drop specific part for PUD-sized transparent hugepages. Support for PUD-sized transparent hugepages was added in v4.11-rc1 ] Signed-off-by: Ben Hutchings ben@decadent.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/huge_memory.c | 14 ++++---------- 1 file changed, 4 insertions(+), 10 deletions(-)
--- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1304,17 +1304,11 @@ struct page *follow_trans_huge_pmd(struc VM_BUG_ON_PAGE(!PageHead(page), page); if (flags & FOLL_TOUCH) { pmd_t _pmd; - /* - * We should set the dirty bit only for FOLL_WRITE but - * for now the dirty bit in the pmd is meaningless. - * And if the dirty bit will become meaningful and - * we'll only set it with FOLL_WRITE, an atomic - * set_bit will be required on the pmd to set the - * young bit, instead of the current set_pmd_at. - */ - _pmd = pmd_mkyoung(pmd_mkdirty(*pmd)); + _pmd = pmd_mkyoung(*pmd); + if (flags & FOLL_WRITE) + _pmd = pmd_mkdirty(_pmd); if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK, - pmd, _pmd, 1)) + pmd, _pmd, flags & FOLL_WRITE)) update_mmu_cache_pmd(vma, addr, pmd); } if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {