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From: Bang Li <libang.linuxer@gmail.com>
To: vgupta@kernel.org
Cc: peterz@infradead.org, mingo@kernel.org,
	valentin.schneider@arm.com, linux-snps-arc@lists.infradead.org,
	linux-kernel@vger.kernel.org, Bang Li <libang.linuxer@gmail.com>
Subject: [PATCH] ARC: remove redundant READ_ONCE() in cmpxchg loop
Date: Sat, 19 Mar 2022 10:03:16 +0800	[thread overview]
Message-ID: <20220319020316.142479-1-libang.linuxer@gmail.com> (raw)

This patch reverts commit 7082a29c22ac ("ARC: use ACCESS_ONCE in cmpxchg
loop").

It is not necessary to use READ_ONCE() because cmpxchg contains barrier. We
can get it from commit d57f727264f1 ("ARC: add compiler barrier to LLSC
based cmpxchg").

Signed-off-by: Bang Li <libang.linuxer@gmail.com>
---
 arch/arc/kernel/smp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arc/kernel/smp.c b/arch/arc/kernel/smp.c
index 78e6d069b1c1..56c23f3e1309 100644
--- a/arch/arc/kernel/smp.c
+++ b/arch/arc/kernel/smp.c
@@ -274,7 +274,7 @@ static void ipi_send_msg_one(int cpu, enum ipi_msg_type msg)
 	 * and read back old value
 	 */
 	do {
-		new = old = READ_ONCE(*ipi_data_ptr);
+		new = old = *ipi_data_ptr;
 		new |= 1U << msg;
 	} while (cmpxchg(ipi_data_ptr, old, new) != old);
 
-- 
2.25.1


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WARNING: multiple messages have this Message-ID (diff)
From: Bang Li <libang.linuxer@gmail.com>
To: vgupta@kernel.org
Cc: peterz@infradead.org, mingo@kernel.org,
	valentin.schneider@arm.com, linux-snps-arc@lists.infradead.org,
	linux-kernel@vger.kernel.org, Bang Li <libang.linuxer@gmail.com>
Subject: [PATCH] ARC: remove redundant READ_ONCE() in cmpxchg loop
Date: Sat, 19 Mar 2022 10:03:16 +0800	[thread overview]
Message-ID: <20220319020316.142479-1-libang.linuxer@gmail.com> (raw)

This patch reverts commit 7082a29c22ac ("ARC: use ACCESS_ONCE in cmpxchg
loop").

It is not necessary to use READ_ONCE() because cmpxchg contains barrier. We
can get it from commit d57f727264f1 ("ARC: add compiler barrier to LLSC
based cmpxchg").

Signed-off-by: Bang Li <libang.linuxer@gmail.com>
---
 arch/arc/kernel/smp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arc/kernel/smp.c b/arch/arc/kernel/smp.c
index 78e6d069b1c1..56c23f3e1309 100644
--- a/arch/arc/kernel/smp.c
+++ b/arch/arc/kernel/smp.c
@@ -274,7 +274,7 @@ static void ipi_send_msg_one(int cpu, enum ipi_msg_type msg)
 	 * and read back old value
 	 */
 	do {
-		new = old = READ_ONCE(*ipi_data_ptr);
+		new = old = *ipi_data_ptr;
 		new |= 1U << msg;
 	} while (cmpxchg(ipi_data_ptr, old, new) != old);
 
-- 
2.25.1


             reply	other threads:[~2022-03-19  2:03 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-19  2:03 Bang Li [this message]
2022-03-19  2:03 ` [PATCH] ARC: remove redundant READ_ONCE() in cmpxchg loop Bang Li
2022-04-18 19:19 ` Vineet Gupta
2022-04-18 19:19   ` Vineet Gupta

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