[3.13.y.z extended stable] Patch "ARM: 8027/1: fix do_div() bug in big-endian systems" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    ARM: 8027/1: fix do_div() bug in big-endian systems

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.3.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From bd10e91dde183768d38ae596d9704935356556d0 Mon Sep 17 00:00:00 2001
From: Xiangyu Lu <luxiangyu at huawei.com>
Date: Tue, 15 Apr 2014 09:38:17 +0100
Subject: ARM: 8027/1: fix do_div() bug in big-endian systems

commit 80bb3ef109ff40a7593d9481c17de9bbc4d7c0e2 upstream.

In big-endian systems, "%1" get the most significant part of the value, cause the instruction to get the wrong result.

When viewing ftrace record in big-endian ARM systems, we found that
the timestamp errors:

swapper-0   [001] 1325.970000:   0:120:R ==> [001]    16:120:R events/1
events/1-16 [001] 1325.970000:   16:120:S ==> [001]    0:120:R swapper
swapper-0   [000] 1325.1000000:  0:120:R   + [000]    15:120:R events/0
swapper-0   [000] 1325.1000000:  0:120:R ==> [000]    15:120:R events/0
swapper-0   [000] 1326.030000:   0:120:R   + [000]  1150:120:R sshd
swapper-0   [000] 1326.030000:   0:120:R ==> [000]  1150:120:R sshd

When viewed ftrace records, it will call the do_div(n, base) function, which achieved arch/arm/include/asm/div64.h in. When n = 10000000, base = 1000000, in do_div(n, base) will execute "umull %Q0, %R0, %1, %Q2".

Reviewed-by: Dave Martin <Dave.Martin at arm.com>
Reviewed-by: Nicolas Pitre <nico at linaro.org>
Signed-off-by: Alex Wu <wuquanming at huawei.com>
Signed-off-by: Xiangyu Lu <luxiangyu at huawei.com>
Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/arm/include/asm/div64.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/div64.h b/arch/arm/include/asm/div64.h
index 191ada6..662c7bd 100644
--- a/arch/arm/include/asm/div64.h
+++ b/arch/arm/include/asm/div64.h
@@ -156,7 +156,7 @@
 		/* Select the best insn combination to perform the   */	\
 		/* actual __m * __n / (__p << 64) operation.         */	\
 		if (!__c) {						\
-			asm (	"umull	%Q0, %R0, %1, %Q2\n\t"		\
+			asm (	"umull	%Q0, %R0, %Q1, %Q2\n\t"		\
 				"mov	%Q0, #0"			\
 				: "=&r" (__res)				\
 				: "r" (__m), "r" (__n)			\
--
1.9.1