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From: Xishi Qiu <qiuxishi@huawei.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	Yaowei Bai <baiyaowei@cmss.chinamobile.com>
Cc: Linux MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Yisheng Xie <xieyisheng1@huawei.com>
Subject: [RFC PATCH v2] mm: use ACCESS_ONCE in page_cpupid_xchg_last()
Date: Mon, 5 Dec 2016 17:26:55 +0800	[thread overview]
Message-ID: <584532DF.7080805@huawei.com> (raw)
In-Reply-To: <0cc3c2bb-e292-2d7b-8d44-16c8e6c19899@de.ibm.com>

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 <qiuxishi@huawei.com>
Suggested-by: Christian Borntraeger <borntraeger@de.ibm.com>
---
 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



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WARNING: multiple messages have this Message-ID (diff)
From: Xishi Qiu <qiuxishi@huawei.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	"Yaowei Bai" <baiyaowei@cmss.chinamobile.com>
Cc: Linux MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Yisheng Xie <xieyisheng1@huawei.com>
Subject: [RFC PATCH v2] mm: use ACCESS_ONCE in page_cpupid_xchg_last()
Date: Mon, 5 Dec 2016 17:26:55 +0800	[thread overview]
Message-ID: <584532DF.7080805@huawei.com> (raw)
In-Reply-To: <0cc3c2bb-e292-2d7b-8d44-16c8e6c19899@de.ibm.com>

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 <qiuxishi@huawei.com>
Suggested-by: Christian Borntraeger <borntraeger@de.ibm.com>
---
 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

  parent reply	other threads:[~2016-12-05  9:39 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-12-05  8:23 [RFC PATCH] mm: use ACCESS_ONCE in page_cpupid_xchg_last() Xishi Qiu
2016-12-05  8:23 ` Xishi Qiu
2016-12-05  8:31 ` Christian Borntraeger
2016-12-05  8:31   ` Christian Borntraeger
2016-12-05  8:50   ` Christian Borntraeger
2016-12-05  8:50     ` Christian Borntraeger
2016-12-05  9:22     ` Xishi Qiu
2016-12-05  9:22       ` Xishi Qiu
2016-12-05  9:26     ` Xishi Qiu [this message]
2016-12-05  9:26       ` [RFC PATCH v2] " Xishi Qiu
2016-12-05  9:44       ` Christian Borntraeger
2016-12-05  9:44         ` Christian Borntraeger
2016-12-06  1:53 ` [RFC PATCH v3] mm: use READ_ONCE " Xishi Qiu
2016-12-06  1:53   ` Xishi Qiu
2016-12-07  8:39   ` Vlastimil Babka
2016-12-07  8:39     ` Vlastimil Babka
2016-12-07  8:43   ` Michal Hocko
2016-12-07  8:43     ` Michal Hocko
2016-12-07  8:48     ` Vlastimil Babka
2016-12-07  8:48       ` Vlastimil Babka
2016-12-07  8:58       ` Michal Hocko
2016-12-07  8:58         ` Michal Hocko
2016-12-07  9:29         ` Vlastimil Babka
2016-12-07  9:29           ` Vlastimil Babka
2016-12-07  9:40           ` Christian Borntraeger
2016-12-07  9:40             ` Christian Borntraeger
2016-12-07  9:59             ` Michal Hocko
2016-12-07  9:59               ` Michal Hocko
2016-12-07 10:03               ` Christian Borntraeger
2016-12-07 10:03                 ` Christian Borntraeger
2016-12-07 22:16                 ` Rasmus Villemoes
2016-12-07 22:16                   ` Rasmus Villemoes

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