From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f70.google.com (mail-oi0-f70.google.com [209.85.218.70]) by kanga.kvack.org (Postfix) with ESMTP id 4FBDA6B0069 for ; Mon, 5 Dec 2016 20:58:04 -0500 (EST) Received: by mail-oi0-f70.google.com with SMTP id l192so585970292oih.2 for ; Mon, 05 Dec 2016 17:58:04 -0800 (PST) Received: from szxga02-in.huawei.com (szxga02-in.huawei.com. [119.145.14.65]) by mx.google.com with ESMTPS id w21si8048277oia.24.2016.12.05.17.58.01 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 05 Dec 2016 17:58:03 -0800 (PST) Message-ID: <58461A0A.3070504@huawei.com> Date: Tue, 6 Dec 2016 09:53:14 +0800 From: Xishi Qiu MIME-Version: 1.0 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 Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton , Mel Gorman , Yaowei Bai , Christian Borntraeger 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 = READ_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