FAILED: patch "[PATCH] arm64: compat: fix stxr failure case in SWP emulation" failed to apply to 4.2-stable tree

FAILED: patch "[PATCH] arm64: compat: fix stxr failure case in SWP emulation" failed to apply to 4.2-stable tree

[gregkh]

The patch below does not apply to the 4.2-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 589cb22bbedacf325951014c07a35a2b01ca57f6 Mon Sep 17 00:00:00 2001
From: Will Deacon <will.deacon@arm.com>
Date: Thu, 15 Oct 2015 13:55:53 +0100
Subject: [PATCH] arm64: compat: fix stxr failure case in SWP emulation

If the STXR instruction fails in the SWP emulation code, we leave *data
overwritten with the loaded value, therefore corrupting the data written
by a subsequent, successful attempt.

This patch re-jigs the code so that we only write back to *data once we
know that the update has happened.

Cc: <stable@vger.kernel.org>
Fixes: bd35a4adc413 ("arm64: Port SWP/SWPB emulation support from arm")
Reported-by: Shengjiu Wang <shengjiu.wang@freescale.com>
Reported-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/kernel/armv8_deprecated.c b/arch/arm64/kernel/armv8_deprecated.c
index bcee7abac68e..937f5e58a4d3 100644
--- a/arch/arm64/kernel/armv8_deprecated.c
+++ b/arch/arm64/kernel/armv8_deprecated.c
@@ -284,21 +284,23 @@ static void register_insn_emulation_sysctl(struct ctl_table *table)
 	__asm__ __volatile__(					\
 	ALTERNATIVE("nop", SET_PSTATE_PAN(0), ARM64_HAS_PAN,	\
 		    CONFIG_ARM64_PAN)				\
-	"	mov		%w2, %w1\n"			\
-	"0:	ldxr"B"		%w1, [%3]\n"			\
-	"1:	stxr"B"		%w0, %w2, [%3]\n"		\
+	"0:	ldxr"B"		%w2, [%3]\n"			\
+	"1:	stxr"B"		%w0, %w1, [%3]\n"		\
 	"	cbz		%w0, 2f\n"			\
 	"	mov		%w0, %w4\n"			\
+	"	b		3f\n"				\
 	"2:\n"							\
+	"	mov		%w1, %w2\n"			\
+	"3:\n"							\
 	"	.pushsection	 .fixup,\"ax\"\n"		\
 	"	.align		2\n"				\
-	"3:	mov		%w0, %w5\n"			\
-	"	b		2b\n"				\
+	"4:	mov		%w0, %w5\n"			\
+	"	b		3b\n"				\
 	"	.popsection"					\
 	"	.pushsection	 __ex_table,\"a\"\n"		\
 	"	.align		3\n"				\
-	"	.quad		0b, 3b\n"			\
-	"	.quad		1b, 3b\n"			\
+	"	.quad		0b, 4b\n"			\
+	"	.quad		1b, 4b\n"			\
 	"	.popsection\n"					\
 	ALTERNATIVE("nop", SET_PSTATE_PAN(1), ARM64_HAS_PAN,	\
 		CONFIG_ARM64_PAN)				\