[PATCH 3.13 184/187] powerpc/thp: Use ACCESS_ONCE when loading pmdp

Kamal Mostafa
2014-09-15T22:13:57Z

From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>

commit 7e467245bf5226db34c4b12d3cbacfa2f7a15a8b upstream.

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

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
arch/powerpc/mm/hugepage-hash64.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/hugepage-hash64.c b/arch/powerpc/mm/hugepage-hash64.c
index e0da847..7d86c86 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;
--
1.9.1