linux-kernel - [PATCH 7/8] usb, cdc-acm: optimize barrier usage for Rmw atomic bitops

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Message-Id: <20200129181545.25302-1-dave@stgolabs.net>
Date:   Wed, 29 Jan 2020 10:15:45 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     oneukum@...e.com
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        dave@...olabs.net, Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 7/8] usb, cdc-acm: optimize barrier usage for Rmw atomic bitops

We can avoid the unnecessary barrier on non LL/SC architectures,
such as x86. Instead, use the smp_mb__after_atomic() call.

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 drivers/usb/class/cdc-acm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 62f4fb9b362f..0bc4b558f387 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -842,7 +842,7 @@ static void acm_tty_unthrottle(struct tty_struct *tty)
 	clear_bit(ACM_THROTTLED, &acm->flags);
 
 	/* Matches the smp_mb__after_atomic() in acm_read_bulk_callback(). */
-	smp_mb();
+	smp_mb__after_atomic();
 
 	acm_submit_read_urbs(acm, GFP_KERNEL);
 }
-- 
2.16.4