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hci_usb.h: fix hard-to-trigger race 

If someone tries to _urb_unlink while _urb_queue_head is running, he'll see
_urb->queue == NULL and fail to do any locking.  Prevent that from happening
by strategically placed barriers.

Signed-off-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Pavel Machek 2008-05-02 16:45:10 -07:00 committed by David S. Miller
parent 84994e16f2
commit 026672d099
1 changed files with 13 additions and 8 deletions
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21
drivers/bluetooth/hci_usb.h
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@ -70,7 +70,8 @@ static inline void _urb_queue_head(struct _urb_queue *q, struct _urb *_urb)
{
unsigned long flags;
spin_lock_irqsave(&q->lock, flags);
list_add(&_urb->list, &q->head); _urb->queue = q;
/* _urb_unlink needs to know which spinlock to use, thus mb(). */
_urb->queue = q; mb(); list_add(&_urb->list, &q->head);
spin_unlock_irqrestore(&q->lock, flags);
}
@ -78,19 +79,23 @@ static inline void _urb_queue_tail(struct _urb_queue *q, struct _urb *_urb)
{
unsigned long flags;
spin_lock_irqsave(&q->lock, flags);
list_add_tail(&_urb->list, &q->head); _urb->queue = q;
/* _urb_unlink needs to know which spinlock to use, thus mb(). */
_urb->queue = q; mb(); list_add_tail(&_urb->list, &q->head);
spin_unlock_irqrestore(&q->lock, flags);
}
static inline void _urb_unlink(struct _urb *_urb)
{
struct _urb_queue *q = _urb->queue;
struct _urb_queue *q;
unsigned long flags;
if (q) {
spin_lock_irqsave(&q->lock, flags);
list_del(&_urb->list); _urb->queue = NULL;
spin_unlock_irqrestore(&q->lock, flags);
}
mb();
q = _urb->queue;
/* If q is NULL, it will die at easy-to-debug NULL pointer dereference.
No need to BUG(). */
spin_lock_irqsave(&q->lock, flags);
list_del(&_urb->list); _urb->queue = NULL;
spin_unlock_irqrestore(&q->lock, flags);
}
struct hci_usb {