This patch fixes a race condition in two utility routines
related to the removal/unlinking of urbs from an anchor.
If two threads are concurrently accessing the same anchor,
both could end up with the same urb - thinking they are
the exclusive owner.
Alan Stern pointed out a related issue in
usb_unlink_anchored_urbs:
"The URB isn't removed from the anchor until it completes
(as a by-product of completion, in fact), which might not
be for quite some time after the unlink call returns.
In the meantime, the subroutine will keep trying to unlink
it, over and over again."
Cc: stable <stable@kernel.org>
Cc: Oliver Neukum <oneukum@suse.de>
Cc: Greg Kroah-Hartman <greg@kroah.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
}
EXPORT_SYMBOL_GPL(usb_anchor_urb);
}
EXPORT_SYMBOL_GPL(usb_anchor_urb);
+/* Callers must hold anchor->lock */
+static void __usb_unanchor_urb(struct urb *urb, struct usb_anchor *anchor)
+{
+ urb->anchor = NULL;
+ list_del(&urb->anchor_list);
+ usb_put_urb(urb);
+ if (list_empty(&anchor->urb_list))
+ wake_up(&anchor->wait);
+}
+
/**
* usb_unanchor_urb - unanchors an URB
* @urb: pointer to the urb to anchor
/**
* usb_unanchor_urb - unanchors an URB
* @urb: pointer to the urb to anchor
return;
spin_lock_irqsave(&anchor->lock, flags);
return;
spin_lock_irqsave(&anchor->lock, flags);
- if (unlikely(anchor != urb->anchor)) {
- /* we've lost the race to another thread */
- spin_unlock_irqrestore(&anchor->lock, flags);
- return;
- }
- urb->anchor = NULL;
- list_del(&urb->anchor_list);
+ /*
+ * At this point, we could be competing with another thread which
+ * has the same intention. To protect the urb from being unanchored
+ * twice, only the winner of the race gets the job.
+ */
+ if (likely(anchor == urb->anchor))
+ __usb_unanchor_urb(urb, anchor);
spin_unlock_irqrestore(&anchor->lock, flags);
spin_unlock_irqrestore(&anchor->lock, flags);
- usb_put_urb(urb);
- if (list_empty(&anchor->urb_list))
- wake_up(&anchor->wait);
}
EXPORT_SYMBOL_GPL(usb_unanchor_urb);
}
EXPORT_SYMBOL_GPL(usb_unanchor_urb);
void usb_unlink_anchored_urbs(struct usb_anchor *anchor)
{
struct urb *victim;
void usb_unlink_anchored_urbs(struct usb_anchor *anchor)
{
struct urb *victim;
- spin_lock_irqsave(&anchor->lock, flags);
- while (!list_empty(&anchor->urb_list)) {
- victim = list_entry(anchor->urb_list.prev, struct urb,
- anchor_list);
- usb_get_urb(victim);
- spin_unlock_irqrestore(&anchor->lock, flags);
- /* this will unanchor the URB */
+ while ((victim = usb_get_from_anchor(anchor)) != NULL) {
usb_unlink_urb(victim);
usb_put_urb(victim);
usb_unlink_urb(victim);
usb_put_urb(victim);
- spin_lock_irqsave(&anchor->lock, flags);
- spin_unlock_irqrestore(&anchor->lock, flags);
}
EXPORT_SYMBOL_GPL(usb_unlink_anchored_urbs);
}
EXPORT_SYMBOL_GPL(usb_unlink_anchored_urbs);
victim = list_entry(anchor->urb_list.next, struct urb,
anchor_list);
usb_get_urb(victim);
victim = list_entry(anchor->urb_list.next, struct urb,
anchor_list);
usb_get_urb(victim);
- spin_unlock_irqrestore(&anchor->lock, flags);
- usb_unanchor_urb(victim);
+ __usb_unanchor_urb(victim, anchor);
- spin_unlock_irqrestore(&anchor->lock, flags);
+ spin_unlock_irqrestore(&anchor->lock, flags);
while (!list_empty(&anchor->urb_list)) {
victim = list_entry(anchor->urb_list.prev, struct urb,
anchor_list);
while (!list_empty(&anchor->urb_list)) {
victim = list_entry(anchor->urb_list.prev, struct urb,
anchor_list);
- usb_get_urb(victim);
- spin_unlock_irqrestore(&anchor->lock, flags);
- /* this may free the URB */
- usb_unanchor_urb(victim);
- usb_put_urb(victim);
- spin_lock_irqsave(&anchor->lock, flags);
+ __usb_unanchor_urb(victim, anchor);
}
spin_unlock_irqrestore(&anchor->lock, flags);
}
}
spin_unlock_irqrestore(&anchor->lock, flags);
}