From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wj0-f198.google.com (mail-wj0-f198.google.com [209.85.210.198]) by kanga.kvack.org (Postfix) with ESMTP id 3480B6B0038 for ; Mon, 5 Dec 2016 04:39:23 -0500 (EST) Received: by mail-wj0-f198.google.com with SMTP id xr1so61202896wjb.7 for ; Mon, 05 Dec 2016 01:39:23 -0800 (PST) Received: from szxga01-in.huawei.com (szxga01-in.huawei.com. [58.251.152.64]) by mx.google.com with ESMTP id xu5si14201109wjb.254.2016.12.05.01.39.20 for ; Mon, 05 Dec 2016 01:39:22 -0800 (PST) Message-ID: <584532DF.7080805@huawei.com> Date: Mon, 5 Dec 2016 17:26:55 +0800 From: Xishi Qiu MIME-Version: 1.0 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 Sender: owner-linux-mm@kvack.org List-ID: To: Christian Borntraeger , Andrew Morton , Mel Gorman , Yaowei Bai Cc: Linux MM , LKML , Yisheng Xie 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org