4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[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@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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)) {