linux-kernel - [PATCH 4.7 169/184] sh: cmpxchg: fix a bit shift bug in big

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Date:   Thu, 22 Sep 2016 19:41:43 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Rich Felker <dalias@...c.org>
Subject: [PATCH 4.7 169/184] sh: cmpxchg: fix a bit shift bug in big_endian os

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

------------------

From: Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>

commit ff18143ceed3424b7d6cdb8659b9692fa734f0d8 upstream.

Correct bitoff in big endian OS.
Current code works correctly for 1 byte but not for 2 bytes.

Fixes: 3226aad81aa6 ("sh: support 1 and 2 byte xchg")
Signed-off-by: Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
Acked-by: Michael S. Tsirkin <mst@...hat.com>
Signed-off-by: Rich Felker <dalias@...c.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/sh/include/asm/cmpxchg-xchg.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/sh/include/asm/cmpxchg-xchg.h
+++ b/arch/sh/include/asm/cmpxchg-xchg.h
@@ -21,7 +21,7 @@ static inline u32 __xchg_cmpxchg(volatil
 	int off = (unsigned long)ptr % sizeof(u32);
 	volatile u32 *p = ptr - off;
 #ifdef __BIG_ENDIAN
-	int bitoff = (sizeof(u32) - 1 - off) * BITS_PER_BYTE;
+	int bitoff = (sizeof(u32) - size - off) * BITS_PER_BYTE;
 #else
 	int bitoff = off * BITS_PER_BYTE;
 #endif