From: Will Deacon <will.deacon@arm.com>
Date: Mon, 30 Apr 2018 13:56:32 +0100
Subject: arm64: cmpwait: Clear event register before arming exclusive monitor
Git-commit: 1cfc63b5ae60fe7e01773f38132f98d8b13a99a0
Patch-mainline: v4.18-rc1
References: git-fixes

When waiting for a cacheline to change state in cmpwait, we may immediately
wake-up the first time around the outer loop if the event register was
already set (for example, because of the event stream).

Avoid these spurious wakeups by explicitly clearing the event register
before loading the cacheline and setting the exclusive monitor.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Ivan T. Ivanov <iivanov@suse.de>
---
 arch/arm64/include/asm/cmpxchg.h |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/arm64/include/asm/cmpxchg.h
+++ b/arch/arm64/include/asm/cmpxchg.h
@@ -229,7 +229,9 @@ static inline void __cmpwait_case_##name
 	unsigned long tmp;						\
 									\
 	asm volatile(							\
-	"	ldxr" #sz "\t%" #w "[tmp], %[v]\n"		\
+	"	sevl\n"							\
+	"	wfe\n"							\
+	"	ldxr" #sz "\t%" #w "[tmp], %[v]\n"			\
 	"	eor	%" #w "[tmp], %" #w "[tmp], %" #w "[val]\n"	\
 	"	cbnz	%" #w "[tmp], 1f\n"				\
 	"	wfe\n"							\