linux-kernel - [RFC][PATCH v2 6/8] x86: don't reload after cmpxchg in unsafe_atomic

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Message-Id: <20200327022836.881203-6-viro@ZenIV.linux.org.uk>
Date:   Fri, 27 Mar 2020 02:28:34 +0000
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [RFC][PATCH v2 6/8] x86: don't reload after cmpxchg in unsafe_atomic_op2() loop

From: Al Viro <viro@...iv.linux.org.uk>

lock cmpxchg leaves the current value in eax; no need to reload it.

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 arch/x86/include/asm/futex.h | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/futex.h b/arch/x86/include/asm/futex.h
index 53c07ab63762..d5d36f408ad0 100644
--- a/arch/x86/include/asm/futex.h
+++ b/arch/x86/include/asm/futex.h
@@ -34,17 +34,17 @@ do {								\
 do {								\
 	int oldval = 0, ret, tem;				\
 	asm volatile("1:\tmovl	%2, %0\n"			\
-		     "\tmovl\t%0, %3\n"				\
+		     "2:\tmovl\t%0, %3\n"			\
 		     "\t" insn "\n"				\
-		     "2:\t" LOCK_PREFIX "cmpxchgl %3, %2\n"	\
-		     "\tjnz\t1b\n"				\
-		     "3:\n"					\
+		     "3:\t" LOCK_PREFIX "cmpxchgl %3, %2\n"	\
+		     "\tjnz\t2b\n"				\
+		     "4:\n"					\
 		     "\t.section .fixup,\"ax\"\n"		\
-		     "4:\tmov\t%5, %1\n"			\
+		     "5:\tmov\t%5, %1\n"			\
 		     "\tjmp\t3b\n"				\
 		     "\t.previous\n"				\
-		     _ASM_EXTABLE_UA(1b, 4b)			\
-		     _ASM_EXTABLE_UA(2b, 4b)			\
+		     _ASM_EXTABLE_UA(1b, 5b)			\
+		     _ASM_EXTABLE_UA(3b, 5b)			\
 		     : "=&a" (oldval), "=&r" (ret),		\
 		       "+m" (*uaddr), "=&r" (tem)		\
 		     : "r" (oparg), "i" (-EFAULT), "1" (0));	\
-- 
2.11.0