mm/hugetlb: add migration/hwpoisoned entry check in hugetlb_change_protection

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.  HWPoison entries also can cause the same
problem.

This patch adds is_hugetlb_entry_(migration|hwpoisoned) check in this
function to do proper actions.

Fixes: 290408d4a2 ("hugetlb: hugepage migration core")
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Steve Capper <steve.capper@linaro.org>
Cc: <stable@vger.kernel.org>	[2.6.36+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 20 insertions, 1 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 385c3a1aced7..c2970e7eb527 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3384,7 +3384,26 @@ 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_hwpoisoned(pte))) {
+                        spin_unlock(ptl);
+                        continue;
+                }
+                if (unlikely(is_hugetlb_entry_migration(pte))) {
+                        swp_entry_t entry = pte_to_swp_entry(pte);
+
+                        if (is_write_migration_entry(entry)) {
+                                pte_t newpte;
+
+                                make_migration_entry_read(&entry);
+                                newpte = swp_entry_to_pte(entry);
+                                set_huge_pte_at(mm, address, ptep, newpte);
+                                pages++;
+                        }
+                        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);