From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752236AbcLFBxj (ORCPT ); Mon, 5 Dec 2016 20:53:39 -0500 Received: from szxga02-in.huawei.com ([119.145.14.65]:38759 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751515AbcLFBxg (ORCPT ); Mon, 5 Dec 2016 20:53:36 -0500 Message-ID: <58461A0A.3070504@huawei.com> Date: Tue, 6 Dec 2016 09:53:14 +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: Andrew Morton , Mel Gorman , Yaowei Bai , Christian Borntraeger CC: Linux MM , LKML , Yisheng Xie Subject: [RFC PATCH v3] mm: use READ_ONCE in page_cpupid_xchg_last() References: <584523E4.9030600@huawei.com> In-Reply-To: <584523E4.9030600@huawei.com> Content-Type: text/plain; charset="ISO-8859-1" 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 = READ_ONCE(page->flags); last_cpupid = page_cpupid_last(page); flags &= ~(LAST_CPUPID_MASK << LAST_CPUPID_PGSHIFT); -- 1.8.3.1