From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757596AbaIOWN5 (ORCPT ); Mon, 15 Sep 2014 18:13:57 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:50791 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755427AbaIOWNw (ORCPT ); Mon, 15 Sep 2014 18:13:52 -0400 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: "Aneesh Kumar K.V" , Benjamin Herrenschmidt , Kamal Mostafa Subject: [PATCH 3.13 184/187] powerpc/thp: Use ACCESS_ONCE when loading pmdp Date: Mon, 15 Sep 2014 15:09:54 -0700 Message-Id: <1410818997-9432-185-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1410818997-9432-1-git-send-email-kamal@canonical.com> References: <1410818997-9432-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.13 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.13.11.7 -stable review patch. If anyone has any objections, please let me know. ------------------ From: "Aneesh Kumar K.V" 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 Signed-off-by: Benjamin Herrenschmidt Signed-off-by: Kamal Mostafa --- 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