powerpc/thp: Use ACCESS_ONCE when loading pmdp

We would get wrong results in compiler recomputed old_pmd. Avoid
that by using ACCESS_ONCE

CC: <stable@vger.kernel.org>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/arch/powerpc/mm/hugepage-hash64.c b/arch/powerpc/mm/hugepage-hash64.c
index 1fb609dcc49b..5f5e6328c21c 100644
--- a/arch/powerpc/mm/hugepage-hash64.c
+++ b/arch/powerpc/mm/hugepage-hash64.c
@@ -84,7 +84,9 @@ int __hash_page_thp(unsigned long ea, unsigned long access, unsigned long vsid,
          * atomically mark the linux large page PMD busy and dirty
          */
         do {
-                old_pmd = pmd_val(*pmdp);
+                pmd_t pmd = ACCESS_ONCE(*pmdp);
+
+                old_pmd = pmd_val(pmd);
                 /* If PMD busy, retry the access */
                 if (unlikely(old_pmd & _PAGE_BUSY))
                         return 0;