USB: extension of anchor API to unpoison an anchor

This extension allows unpoisoning an anchor allowing drivers that
resubmit URBs to reuse an anchor for methods like resume()

Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/core/urb.c

@@ -678,6 +678,26 @@ void usb_poison_anchored_urbs(struct usb_anchor *anchor)
 }
 EXPORT_SYMBOL_GPL(usb_poison_anchored_urbs);
 
+/**
+ * usb_unpoison_anchored_urbs - let an anchor be used successfully again
+ * @anchor: anchor the requests are bound to
+ *
+ * Reverses the effect of usb_poison_anchored_urbs
+ * the anchor can be used normally after it returns
+ */
+void usb_unpoison_anchored_urbs(struct usb_anchor *anchor)
+{
+	unsigned long flags;
+	struct urb *lazarus;
+
+	spin_lock_irqsave(&anchor->lock, flags);
+	list_for_each_entry(lazarus, &anchor->urb_list, anchor_list) {
+		usb_unpoison_urb(lazarus);
+	}
+	anchor->poisoned = 0;
+	spin_unlock_irqrestore(&anchor->lock, flags);
+}
+EXPORT_SYMBOL_GPL(usb_unpoison_anchored_urbs);
 /**
  * usb_unlink_anchored_urbs - asynchronously cancel transfer requests en masse
  * @anchor: anchor the requests are bound to