From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Aneesh Kumar K.V" , Benjamin Herrenschmidt Subject: [PATCH 3.14 030/114] powerpc/thp: Use ACCESS_ONCE when loading pmdp Date: Mon, 15 Sep 2014 12:25:30 -0700 Message-Id: <20140915192642.377569032@linuxfoundation.org> In-Reply-To: <20140915192641.428509513@linuxfoundation.org> References: <20140915192641.428509513@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.14-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: Greg Kroah-Hartman --- arch/powerpc/mm/hugepage-hash64.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- 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, un * 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;