From b318d41f1bd10bf10c71c350d41eed4f6da133a8 Mon Sep 17 00:00:00 2001
From: Heiko Carstens <hca@linux.ibm.com>
Date: Mon, 9 Jan 2023 11:51:20 +0100
Subject: [PATCH] s390/percpu: add READ_ONCE() to arch_this_cpu_to_op_simple()

commit e3f360db08d55a14112bd27454e616a24296a8b0 upstream.

Make sure that *ptr__ within arch_this_cpu_to_op_simple() is only
dereferenced once by using READ_ONCE(). Otherwise the compiler could
generate incorrect code.

Cc: <stable@vger.kernel.org>
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/s390/include/asm/percpu.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/s390/include/asm/percpu.h b/arch/s390/include/asm/percpu.h
index 918f0ba4f4d20..5e26e2c4641b4 100644
--- a/arch/s390/include/asm/percpu.h
+++ b/arch/s390/include/asm/percpu.h
@@ -31,7 +31,7 @@
 	pcp_op_T__ *ptr__;						\
 	preempt_disable_notrace();					\
 	ptr__ = raw_cpu_ptr(&(pcp));					\
-	prev__ = *ptr__;						\
+	prev__ = READ_ONCE(*ptr__);					\
 	do {								\
 		old__ = prev__;						\
 		new__ = old__ op (val);					\