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From:   Junru Shen <hhusjrsjr@gmail.com>
To:     Will Deacon <will@kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H . Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org,
        Junru Shen <hhusjrsjr@gmail.com>
Subject: [PATCH] atomic: Put the fetching of the old value into the loop when doing atomic CAS
Date:   Thu, 24 Feb 2022 16:24:07 +0800
Message-Id: <20220224082407.580121-1-hhusjrsjr@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Put the acquisition of the expected value inside the loop to prevent an infinite loop when it does not match.

Signed-off-by: Junru Shen <hhusjrsjr@gmail.com>
---
 arch/x86/include/asm/atomic64_64.h | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/atomic64_64.h b/arch/x86/include/asm/atomic64_64.h
index 7886d0578..3df04c44c 100644
--- a/arch/x86/include/asm/atomic64_64.h
+++ b/arch/x86/include/asm/atomic64_64.h
@@ -207,9 +207,10 @@ static inline void arch_atomic64_and(s64 i, atomic64_t *v)
 
 static inline s64 arch_atomic64_fetch_and(s64 i, atomic64_t *v)
 {
-	s64 val = arch_atomic64_read(v);
+	s64 val;
 
 	do {
+		val = arch_atomic64_read(v);
 	} while (!arch_atomic64_try_cmpxchg(v, &val, val & i));
 	return val;
 }
@@ -225,9 +226,10 @@ static inline void arch_atomic64_or(s64 i, atomic64_t *v)
 
 static inline s64 arch_atomic64_fetch_or(s64 i, atomic64_t *v)
 {
-	s64 val = arch_atomic64_read(v);
+	s64 val;
 
 	do {
+		val = arch_atomic64_read(v);
 	} while (!arch_atomic64_try_cmpxchg(v, &val, val | i));
 	return val;
 }
@@ -243,9 +245,10 @@ static inline void arch_atomic64_xor(s64 i, atomic64_t *v)
 
 static inline s64 arch_atomic64_fetch_xor(s64 i, atomic64_t *v)
 {
-	s64 val = arch_atomic64_read(v);
+	s64 val;
 
 	do {
+		val = arch_atomic64_read(v);
 	} while (!arch_atomic64_try_cmpxchg(v, &val, val ^ i));
 	return val;
 }
-- 
2.30.2