linux-kernel - [PATCH 3.12 057/142] powerpc/thp: Use ACCESS

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Message-Id: <9de1fa60881dc08bd562aa3b1a31e42829eb8dd1.1411724724.git.jslaby@suse.cz>
Date:	Fri, 26 Sep 2014 11:44:28 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 057/142] powerpc/thp: Use ACCESS_ONCE when loading pmdp

From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 7e467245bf5226db34c4b12d3cbacfa2f7a15a8b upstream.

We would get wrong results in compiler recomputed old_pmd. Avoid
that by using ACCESS_ONCE

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 arch/powerpc/mm/hugepage-hash64.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/hugepage-hash64.c b/arch/powerpc/mm/hugepage-hash64.c
index e0da84719b46..7d86c868040d 100644
--- a/arch/powerpc/mm/hugepage-hash64.c
+++ b/arch/powerpc/mm/hugepage-hash64.c
@@ -84,7 +84,9 @@ int __hash_page_thp(unsigned long ea, unsigned long access, unsigned long vsid,
 	 * atomically mark the linux large page PMD busy and dirty
 	 */
 	do {
-		old_pmd = pmd_val(*pmdp);
+		pmd_t pmd = ACCESS_ONCE(*pmdp);
+
+		old_pmd = pmd_val(pmd);
 		/* If PMD busy, retry the access */
 		if (unlikely(old_pmd & _PAGE_BUSY))
 			return 0;
-- 
2.1.0

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