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authorChristian Lamparter <chunkeey@googlemail.com>2010-08-03 02:32:28 +0200
committerGreg Kroah-Hartman <gregkh@suse.de>2010-08-13 13:31:01 -0700
commit8762dc2878fcdab3a3d71502c42e5923c79e8086 (patch)
tree7ab01435f3e31d8eea4a1250ba20e633cc18c56e
parent733677e180eb390067ae5f53ef9ff7396aa8a07b (diff)
downloadlinux-2.6.34-ux500-8762dc2878fcdab3a3d71502c42e5923c79e8086.tar.gz
USB: fix thread-unsafe anchor utiliy routines
commit b3e670443b7fb8a2d29831b62b44a039c283e351 upstream. 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: 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>
-rw-r--r--drivers/usb/core/urb.c50
1 files changed, 21 insertions, 29 deletions
diff --git a/drivers/usb/core/urb.c b/drivers/usb/core/urb.c
index 7c0555548ac..419e6b34e2f 100644
--- a/drivers/usb/core/urb.c
+++ b/drivers/usb/core/urb.c
@@ -137,6 +137,16 @@ void usb_anchor_urb(struct urb *urb, struct usb_anchor *anchor)
}
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
@@ -156,17 +166,14 @@ void usb_unanchor_urb(struct urb *urb)
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);
- usb_put_urb(urb);
- if (list_empty(&anchor->urb_list))
- wake_up(&anchor->wait);
}
EXPORT_SYMBOL_GPL(usb_unanchor_urb);
@@ -749,20 +756,11 @@ EXPORT_SYMBOL_GPL(usb_unpoison_anchored_urbs);
void usb_unlink_anchored_urbs(struct usb_anchor *anchor)
{
struct urb *victim;
- unsigned long flags;
- 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);
- spin_lock_irqsave(&anchor->lock, flags);
}
- spin_unlock_irqrestore(&anchor->lock, flags);
}
EXPORT_SYMBOL_GPL(usb_unlink_anchored_urbs);
@@ -799,12 +797,11 @@ struct urb *usb_get_from_anchor(struct usb_anchor *anchor)
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);
} else {
- spin_unlock_irqrestore(&anchor->lock, flags);
victim = NULL;
}
+ spin_unlock_irqrestore(&anchor->lock, flags);
return victim;
}
@@ -826,12 +823,7 @@ void usb_scuttle_anchored_urbs(struct usb_anchor *anchor)
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);
}