[PATCH v2 3/3] mm/hugetlb: add migration entry check in hugetlb_change_protection

[Naoya Horiguchi]

There is a race condition between hugepage migration and change_protection(),
where hugetlb_change_protection() doesn't care about migration entries and
wrongly overwrites them. That causes unexpected results like kernel crash.

This patch adds is_hugetlb_entry_(migration|hwpoisoned) check in this
function and skip all such entries.

Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>  # [3.12+]
---
 mm/hugetlb.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git mmotm-2014-07-22-15-58.orig/mm/hugetlb.c mmotm-2014-07-22-15-58/mm/hugetlb.c
index 863f45f63cd5..1da7ca2e2a02 100644
--- mmotm-2014-07-22-15-58.orig/mm/hugetlb.c
+++ mmotm-2014-07-22-15-58/mm/hugetlb.c
@@ -3355,7 +3355,13 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
 			spin_unlock(ptl);
 			continue;
 		}
-		if (!huge_pte_none(huge_ptep_get(ptep))) {
+		pte = huge_ptep_get(ptep);
+		if (unlikely(is_hugetlb_entry_migration(pte) ||
+			     is_hugetlb_entry_hwpoisoned(pte))) {
+			spin_unlock(ptl);
+			continue;
+		}
+		if (!huge_pte_none(pte)) {
 			pte = huge_ptep_get_and_clear(mm, address, ptep);
 			pte = pte_mkhuge(huge_pte_modify(pte, newprot));
 			pte = arch_make_huge_pte(pte, vma, NULL, 0);
-- 
1.9.3

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