linux-kernel - [PATCH V7 1/5] asm-generic: ticket-lock: Remove unnecessary atomic

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Message-Id: <20220628081707.1997728-2-guoren@kernel.org>
Date:   Tue, 28 Jun 2022 04:17:03 -0400
From:   guoren@...nel.org
To:     palmer@...osinc.com, arnd@...db.de, mingo@...hat.com,
        will@...nel.org, longman@...hat.com, boqun.feng@...il.com
Cc:     linux-riscv@...ts.infradead.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, Guo Ren <guoren@...ux.alibaba.com>,
        Guo Ren <guoren@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH V7 1/5] asm-generic: ticket-lock: Remove unnecessary atomic_read

From: Guo Ren <guoren@...ux.alibaba.com>

Remove unnecessary atomic_read in arch_spin_value_unlocked(lock),
because the value has been in lock. This patch could prevent
arch_spin_value_unlocked contend spin_lock data again.

Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
Signed-off-by: Guo Ren <guoren@...nel.org>
Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Palmer Dabbelt <palmer@...osinc.com>
---
 include/asm-generic/spinlock.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/asm-generic/spinlock.h b/include/asm-generic/spinlock.h
index fdfebcb050f4..f1e4fa100f5a 100644
--- a/include/asm-generic/spinlock.h
+++ b/include/asm-generic/spinlock.h
@@ -84,7 +84,9 @@ static __always_inline int arch_spin_is_contended(arch_spinlock_t *lock)
 
 static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
 {
-	return !arch_spin_is_locked(&lock);
+	u32 val = lock.counter;
+
+	return ((val >> 16) == (val & 0xffff));
 }
 
 #include <asm/qrwlock.h>
-- 
2.36.1