From: guoren@kernel.org
To: chenhuacai@kernel.or, kernel@xen0n.name, arnd@arndb.de,
andi.shyti@linux.intel.com, wangrui@loongson.cn,
andrzej.hajda@intel.com, peterz@infradead.org, will@kernel.org,
boqun.feng@gmail.com, mark.rutland@arm.com, guoren@kernel.org
Cc: loongarch@lists.linux.dev, linux-kernel@vger.kernel.org,
Guo Ren <guoren@linux.alibaba.com>
Subject: [PATCH] LoongArch: Fixup cmpxchg sematic for memory barrier
Date: Mon, 31 Jul 2023 21:15:54 -0400 [thread overview]
Message-ID: <20230801011554.3950435-1-guoren@kernel.org> (raw)
From: Guo Ren <guoren@linux.alibaba.com>
When cmpxchg failed, no memory barrier was needed to take. Only
when cmpxchg success and the new value is written, then the memory
barriers needed.
- cmpxchg_asm: Unnecessary __WEAK_LLSC_WB for the fail path would
reduce the performance of the cmpxchg loop trying.
- cmpxchg_small: Miss an necessary __WEAK_LLSC_WB when sc succeeds.
It's a bug because there is no memory synchronization
when sc succeeds.
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
---
arch/loongarch/include/asm/cmpxchg.h | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/arch/loongarch/include/asm/cmpxchg.h b/arch/loongarch/include/asm/cmpxchg.h
index 979fde61bba8..6a05b92814b6 100644
--- a/arch/loongarch/include/asm/cmpxchg.h
+++ b/arch/loongarch/include/asm/cmpxchg.h
@@ -102,8 +102,8 @@ __arch_xchg(volatile void *ptr, unsigned long x, int size)
" move $t0, %z4 \n" \
" " st " $t0, %1 \n" \
" beqz $t0, 1b \n" \
- "2: \n" \
__WEAK_LLSC_MB \
+ "2: \n" \
: "=&r" (__ret), "=ZB"(*m) \
: "ZB"(*m), "Jr" (old), "Jr" (new) \
: "t0", "memory"); \
@@ -148,10 +148,8 @@ static inline unsigned int __cmpxchg_small(volatile void *ptr, unsigned int old,
" or %1, %1, %z6 \n"
" sc.w %1, %2 \n"
" beqz %1, 1b \n"
- " b 3f \n"
- "2: \n"
__WEAK_LLSC_MB
- "3: \n"
+ "2: \n"
: "=&r" (old32), "=&r" (temp), "=ZC" (*ptr32)
: "ZC" (*ptr32), "Jr" (mask), "Jr" (old), "Jr" (new)
: "memory");
--
2.36.1
next reply other threads:[~2023-08-01 1:16 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-01 1:15 guoren [this message]
2023-08-01 2:29 ` WANG Rui
2023-08-01 8:32 ` Will Deacon
2023-08-01 9:30 ` WANG Rui
2023-08-01 9:02 ` Guo Ren
2023-08-01 9:05 ` Guo Ren
2023-08-01 9:31 ` WANG Rui
2023-08-01 10:49 ` Guo Ren
2023-08-01 11:23 ` Xi Ruoyao
2023-08-01 11:28 ` Xi Ruoyao
2023-08-01 16:36 ` WANG Rui
2023-08-01 23:17 ` Guo Ren
2023-08-02 2:23 ` WANG Rui
2023-08-01 3:10 ` Xi Ruoyao
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