linux-kernel - [PATCH] ARC: remove redundant READ

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Date:   Sat, 19 Mar 2022 10:03:16 +0800
From:   Bang Li <libang.linuxer@...il.com>
To:     vgupta@...nel.org
Cc:     peterz@...radead.org, mingo@...nel.org, valentin.schneider@....com,
        linux-snps-arc@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Bang Li <libang.linuxer@...il.com>
Subject: [PATCH] ARC: remove redundant READ_ONCE() in cmpxchg loop

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@...il.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