releases/3.16.3/powerpc-thp-use-access_once-when-loading-pmdp.patch

   1 From 7e467245bf5226db34c4b12d3cbacfa2f7a15a8b Mon Sep 17 00:00:00 2001
   2 From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
   3 Date: Wed, 13 Aug 2014 12:32:02 +0530
   4 Subject: powerpc/thp: Use ACCESS_ONCE when loading pmdp
   5
   6 From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
   7
   8 commit 7e467245bf5226db34c4b12d3cbacfa2f7a15a8b upstream.
   9
  10 We would get wrong results in compiler recomputed old_pmd. Avoid
  11 that by using ACCESS_ONCE
  12
  13 Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
  14 Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
  15 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  16
  17 ---
  18  arch/powerpc/mm/hugepage-hash64.c |    4 +++-
  19  1 file changed, 3 insertions(+), 1 deletion(-)
  20
  21 --- a/arch/powerpc/mm/hugepage-hash64.c
  22 +++ b/arch/powerpc/mm/hugepage-hash64.c
  23 @@ -84,7 +84,9 @@ int __hash_page_thp(unsigned long ea, un
  24          * atomically mark the linux large page PMD busy and dirty
  25          */
  26         do {
  27 -               old_pmd = pmd_val(*pmdp);
  28 +               pmd_t pmd = ACCESS_ONCE(*pmdp);
  29 +
  30 +               old_pmd = pmd_val(pmd);
  31                 /* If PMD busy, retry the access */
  32                 if (unlikely(old_pmd & _PAGE_BUSY))
  33                         return 0;