linux-kernel - [PATCH] bluetooth: optimize barrier usage for Rmw atomics

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Message-Id: <20200129181041.24853-1-dave@stgolabs.net>
Date:   Wed, 29 Jan 2020 10:10:41 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     marcel@...tmann.org
Cc:     johan.hedberg@...il.com, linux-kernel@...r.kernel.org,
        linux-bluetooth@...r.kernel.org,
        Davidlohr Bueso <dave@...olabs.net>,
        Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH] bluetooth: optimize barrier usage for Rmw atomics

Use smp_mb__before_atomic() instead of smp_mb() and avoid the
unnecessary barrier for non LL/SC architectures, such as x86.

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 net/bluetooth/hidp/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/bluetooth/hidp/core.c b/net/bluetooth/hidp/core.c
index bef84b95e2c4..3b4fa27a44e6 100644
--- a/net/bluetooth/hidp/core.c
+++ b/net/bluetooth/hidp/core.c
@@ -1279,7 +1279,7 @@ static int hidp_session_thread(void *arg)
 	add_wait_queue(sk_sleep(session->intr_sock->sk), &intr_wait);
 	/* This memory barrier is paired with wq_has_sleeper(). See
 	 * sock_poll_wait() for more information why this is needed. */
-	smp_mb();
+	smp_mb__before_atomic();
 
 	/* notify synchronous startup that we're ready */
 	atomic_inc(&session->state);
-- 
2.16.4