hci_usb: replace mb with smp_mb

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@gmail.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/bluetooth/hci_usb.h b/drivers/bluetooth/hci_usb.h
index 1790cc8..8e65991 100644 (file)
--- 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(). */