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Subject: [PATCH v3 1/5] arch,locking/atomic: arc: arch_cmpxchg should check data size
Date:   Tue, 21 Nov 2023 22:23:43 +0800
Message-Id: <20231121142347.241356-2-wuqiang.matt@bytedance.com>
In-Reply-To: <20231121142347.241356-1-wuqiang.matt@bytedance.com>
References: <20231121142347.241356-1-wuqiang.matt@bytedance.com>
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arch_cmpxchg() should check data size rather than pointer size in case
CONFIG_ARC_HAS_LLSC is defined. So rename __cmpxchg to __cmpxchg_32 to
emphasize it's explicit support of 32bit data size with BUILD_BUG_ON()
added to avoid any possible misuses with unsupported data types.

In case CONFIG_ARC_HAS_LLSC is undefined, arch_cmpxchg() uses spinlock
to accomplish SMP-safety, so the BUILD_BUG_ON checking is uncecessary.

v2 -> v3:
  - Patches regrouped and has the improvement for xtensa included
  - Comments refined to address why these changes are needed

v1 -> v2:
  - Try using native cmpxchg variants if avaialble, as Arnd advised

Signed-off-by: wuqiang.matt <wuqiang.matt@bytedance.com>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 arch/arc/include/asm/cmpxchg.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h
index e138fde067de..bf46514f6f12 100644
--- a/arch/arc/include/asm/cmpxchg.h
+++ b/arch/arc/include/asm/cmpxchg.h
@@ -18,14 +18,16 @@
  * if (*ptr == @old)
  *      *ptr = @new
  */
-#define __cmpxchg(ptr, old, new)					\
+#define __cmpxchg_32(ptr, old, new)					\
 ({									\
 	__typeof__(*(ptr)) _prev;					\
 									\
+	BUILD_BUG_ON(sizeof(*(ptr)) != 4);				\
+									\
 	__asm__ __volatile__(						\
-	"1:	llock  %0, [%1]	\n"					\
+	"1:	llock  %0, [%1]		\n"				\
 	"	brne   %0, %2, 2f	\n"				\
-	"	scond  %3, [%1]	\n"					\
+	"	scond  %3, [%1]		\n"				\
 	"	bnz     1b		\n"				\
 	"2:				\n"				\
 	: "=&r"(_prev)	/* Early clobber prevent reg reuse */		\
@@ -47,7 +49,7 @@
 									\
 	switch(sizeof((_p_))) {						\
 	case 4:								\
-		_prev_ = __cmpxchg(_p_, _o_, _n_);			\
+		_prev_ = __cmpxchg_32(_p_, _o_, _n_);			\
 		break;							\
 	default:							\
 		BUILD_BUG();						\
@@ -65,8 +67,6 @@
 	__typeof__(*(ptr)) _prev_;					\
 	unsigned long __flags;						\
 									\
-	BUILD_BUG_ON(sizeof(_p_) != 4);					\
-									\
 	/*								\
 	 * spin lock/unlock provide the needed smp_mb() before/after	\
 	 */								\
-- 
2.40.1