[PATCH] USB: add "present" flag to usb_device structure.

This solves lots of races when drivers hold a reference to the usb_device
after the device is physically removed from the system (like when a user
has a open handle.)  This now prevents any new urbs being submitted or
canceled for the device.

drivers/usb/core/urb.c

@@ -195,7 +195,7 @@ int usb_submit_urb(struct urb *urb, int mem_flags)
 
 	if (!urb || urb->hcpriv || !urb->complete)
 		return -EINVAL;
-	if (!(dev = urb->dev) || !dev->bus || dev->devnum <= 0)
+	if (!(dev = urb->dev) || !dev->present || !dev->bus || dev->devnum <= 0)
 		return -ENODEV;
 	if (!(op = dev->bus->op) || !op->submit_urb)
 		return -ENODEV;
@@ -376,7 +376,7 @@ int usb_submit_urb(struct urb *urb, int mem_flags)
  */
 int usb_unlink_urb(struct urb *urb)
 {
-	if (urb && urb->dev && urb->dev->bus && urb->dev->bus->op)
+	if (urb && urb->dev && urb->dev->present && urb->dev->bus && urb->dev->bus->op)
 		return urb->dev->bus->op->unlink_urb(urb);
 	else
 		return -ENODEV;

drivers/usb/core/usb.c

@@ -679,6 +679,7 @@ struct usb_device *usb_alloc_dev(struct usb_device *parent, struct usb_bus *bus)
 	memset(dev, 0, sizeof(*dev));
 
 	device_initialize(&dev->dev);
+	dev->present = 1;
 
 	usb_bus_get(bus);
 
@@ -854,6 +855,10 @@ void usb_disconnect(struct usb_device **pdev)
 	}
 	device_unregister(&dev->dev);
 
+	/* mark the device as not present so any further urb submissions for
+	 * this device will fail. */
+	dev->present = 0;
+
 	/* Decrement the reference count, it'll auto free everything when */
 	/* it hits 0 which could very well be now */
 	usb_put_dev(dev);

include/linux/usb.h

@@ -239,6 +239,7 @@ struct usb_device {
 
 	int have_langid;		/* whether string_langid is valid yet */
 	int string_langid;		/* language ID for strings */
+	int present;			/* if device is present or not */
 
 	void *hcpriv;			/* Host Controller private data */