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>
diff --git a/drivers/bluetooth/hci_usb.h b/drivers/bluetooth/hci_usb.h
index 414080a..1790cc8 100644
--- a/drivers/bluetooth/hci_usb.h
+++ b/drivers/bluetooth/hci_usb.h
@@ -70,7 +70,8 @@
{
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 @@
{
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 {