mm: vm_page_prot: update with WRITE_ONCE/READ_ONCE

vma->vm_page_prot is read lockless from the rmap_walk, it may be updated
concurrently and this prevents the risk of reading intermediate values.

Link: http://lkml.kernel.org/r/1474660305-19222-1-git-send-email-aarcange@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Jan Vorlicek <janvorli@microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index f7ee04a5ae27..99250aee1ac1 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -234,7 +234,7 @@ static int remove_migration_pte(struct page *new, struct vm_area_struct *vma,
                 goto unlock;
 
         get_page(new);
-        pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
+        pte = pte_mkold(mk_pte(new, READ_ONCE(vma->vm_page_prot)));
         if (pte_swp_soft_dirty(*ptep))
                 pte = pte_mksoft_dirty(pte);