linux-kernel - [PATCH AUTOSEL 4.19 43/50] arm64: fix unreachable code issue with cmpxchg

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Date:   Tue, 24 Sep 2019 12:48:40 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Arnd Bergmann <arnd@...db.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Andrew Murray <andrew.murray@....com>,
        Will Deacon <will@...nel.org>, Sasha Levin <sashal@...nel.org>,
        clang-built-linux@...glegroups.com
Subject: [PATCH AUTOSEL 4.19 43/50] arm64: fix unreachable code issue with cmpxchg

From: Arnd Bergmann <arnd@...db.de>

[ Upstream commit 920fdab7b3ce98c14c840261e364f490f3679a62 ]

On arm64 build with clang, sometimes the __cmpxchg_mb is not inlined
when CONFIG_OPTIMIZE_INLINING is set.
Clang then fails a compile-time assertion, because it cannot tell at
compile time what the size of the argument is:

mm/memcontrol.o: In function `__cmpxchg_mb':
memcontrol.c:(.text+0x1a4c): undefined reference to `__compiletime_assert_175'
memcontrol.c:(.text+0x1a4c): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `__compiletime_assert_175'

Mark all of the cmpxchg() style functions as __always_inline to
ensure that the compiler can see the result.

Acked-by: Nick Desaulniers <ndesaulniers@...gle.com>
Reported-by: Nathan Chancellor <natechancellor@...il.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/648
Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
Tested-by: Nathan Chancellor <natechancellor@...il.com>
Reviewed-by: Andrew Murray <andrew.murray@....com>
Tested-by: Andrew Murray <andrew.murray@....com>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Will Deacon <will@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/arm64/include/asm/cmpxchg.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/cmpxchg.h b/arch/arm64/include/asm/cmpxchg.h
index 3b09382815419..d8b01c7c9cd3f 100644
--- a/arch/arm64/include/asm/cmpxchg.h
+++ b/arch/arm64/include/asm/cmpxchg.h
@@ -74,7 +74,7 @@ __XCHG_CASE( ,  ,  mb_8, dmb ish, nop,  , a, l, "memory")
 #undef __XCHG_CASE
 
 #define __XCHG_GEN(sfx)							\
-static inline unsigned long __xchg##sfx(unsigned long x,		\
+static __always_inline  unsigned long __xchg##sfx(unsigned long x,	\
 					volatile void *ptr,		\
 					int size)			\
 {									\
@@ -116,7 +116,7 @@ __XCHG_GEN(_mb)
 #define xchg(...)		__xchg_wrapper( _mb, __VA_ARGS__)
 
 #define __CMPXCHG_GEN(sfx)						\
-static inline unsigned long __cmpxchg##sfx(volatile void *ptr,		\
+static __always_inline unsigned long __cmpxchg##sfx(volatile void *ptr,	\
 					   unsigned long old,		\
 					   unsigned long new,		\
 					   int size)			\
@@ -223,7 +223,7 @@ __CMPWAIT_CASE( ,  , 8);
 #undef __CMPWAIT_CASE
 
 #define __CMPWAIT_GEN(sfx)						\
-static inline void __cmpwait##sfx(volatile void *ptr,			\
+static __always_inline void __cmpwait##sfx(volatile void *ptr,		\
 				  unsigned long val,			\
 				  int size)				\
 {									\
-- 
2.20.1