linux-kernel - [PATCH] hci_usb:replace mb with smp

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Message-Id: <1217655225-4232-1-git-send-email-tom.leiming@gmail.com>
Date:	Sat,  2 Aug 2008 13:33:45 +0800
From:	tom.leiming@...il.com
To:	marcel@...tmann.org
Cc:	linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ming Lei <tom.leiming@...il.com>
Subject: [PATCH] hci_usb:replace mb with smp_mb

From: Ming Lei <tom.leiming@...il.com>

smp_mb is enough for ordering memory operations among processors,and
mb is more expensive than smp_mb for UP machine, so replace it with
smp_mb().

Signed-off-by: Ming Lei <tom.leiming@...il.com>
---
 drivers/bluetooth/hci_usb.h |   10 +++++-----
 1 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/bluetooth/hci_usb.h b/drivers/bluetooth/hci_usb.h
index 1790cc8..8e65991 100644
--- a/drivers/bluetooth/hci_usb.h
+++ b/drivers/bluetooth/hci_usb.h
@@ -70,8 +70,8 @@ static inline void _urb_queue_head(struct _urb_queue *q, struct _urb *_urb)
 {
 	unsigned long flags;
 	spin_lock_irqsave(&q->lock, flags);
-	/* _urb_unlink needs to know which spinlock to use, thus mb(). */
-	_urb->queue = q; mb(); list_add(&_urb->list, &q->head);
+	/* _urb_unlink needs to know which spinlock to use, thus smp_mb(). */
+	_urb->queue = q; smp_mb(); list_add(&_urb->list, &q->head);
 	spin_unlock_irqrestore(&q->lock, flags);
 }
 
@@ -79,8 +79,8 @@ static inline void _urb_queue_tail(struct _urb_queue *q, struct _urb *_urb)
 {
 	unsigned long flags;
 	spin_lock_irqsave(&q->lock, flags);
-	/* _urb_unlink needs to know which spinlock to use, thus mb(). */
-	_urb->queue = q; mb(); list_add_tail(&_urb->list, &q->head);
+	/* _urb_unlink needs to know which spinlock to use, thus smp_mb(). */
+	_urb->queue = q; smp_mb(); list_add_tail(&_urb->list, &q->head);
 	spin_unlock_irqrestore(&q->lock, flags);
 }
 
@@ -89,7 +89,7 @@ static inline void _urb_unlink(struct _urb *_urb)
 	struct _urb_queue *q;
 	unsigned long flags;
 
-	mb();
+	smp_mb();
 	q = _urb->queue;
 	/* If q is NULL, it will die at easy-to-debug NULL pointer dereference.
 	   No need to BUG(). */
-- 
1.5.6.rc2.45.gdc92c

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