From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752295AbcLEJ1w (ORCPT ); Mon, 5 Dec 2016 04:27:52 -0500 Received: from szxga01-in.huawei.com ([58.251.152.64]:16619 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751372AbcLEJ1b (ORCPT ); Mon, 5 Dec 2016 04:27:31 -0500 Message-ID: <584532DF.7080805@huawei.com> Date: Mon, 5 Dec 2016 17:26:55 +0800 From: Xishi Qiu User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:12.0) Gecko/20120428 Thunderbird/12.0.1 MIME-Version: 1.0 To: Christian Borntraeger , Andrew Morton , Mel Gorman , "Yaowei Bai" CC: Linux MM , LKML , Yisheng Xie Subject: [RFC PATCH v2] mm: use ACCESS_ONCE in page_cpupid_xchg_last() References: <584523E4.9030600@huawei.com> <26c66f28-d836-4d6e-fb40-3e2189a540ed@de.ibm.com> <0cc3c2bb-e292-2d7b-8d44-16c8e6c19899@de.ibm.com> In-Reply-To: <0cc3c2bb-e292-2d7b-8d44-16c8e6c19899@de.ibm.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.177.25.179] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org A compiler could re-read "old_flags" from the memory location after reading and calculation "flags" and passes a newer value into the cmpxchg making the comparison succeed while it should actually fail. Signed-off-by: Xishi Qiu Suggested-by: Christian Borntraeger --- mm/mmzone.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/mmzone.c b/mm/mmzone.c index 5652be8..e0b698e 100644 --- a/mm/mmzone.c +++ b/mm/mmzone.c @@ -102,7 +102,7 @@ int page_cpupid_xchg_last(struct page *page, int cpupid) int last_cpupid; do { - old_flags = flags = page->flags; + old_flags = flags = ACCESS_ONCE(page->flags); last_cpupid = page_cpupid_last(page); flags &= ~(LAST_CPUPID_MASK << LAST_CPUPID_PGSHIFT); -- 1.8.3.1