PCI: Fix reference counting bug

pci_get_subsys() will decrement the reference count of the device that
it starts searching from.  Unfortunately, the pci_find_device() interface
will already have decremented the reference count of the device earlier,
so the device will end up losing all reference counts and be freed.

We can fix this by incrementing the reference count of the device to
start searching from before calling pci_get_subsys().
Signed-off-by: NMatthew Wilcox <willy@linux.intel.com>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>

drivers/pci/search.c

@@ -166,6 +166,7 @@ struct pci_dev *pci_find_device(unsigned int vendor, unsigned int device,
 {
 	struct pci_dev *pdev;
 
+	pci_dev_get(from);
 	pdev = pci_get_subsys(vendor, device, PCI_ANY_ID, PCI_ANY_ID, from);
 	pci_dev_put(pdev);
 	return pdev;
@@ -270,12 +271,8 @@ static struct pci_dev *pci_get_dev_by_id(const struct pci_device_id *id,
 	struct pci_dev *pdev = NULL;
 
 	WARN_ON(in_interrupt());
-	if (from) {
-		/* FIXME
-		 * take the cast off, when bus_find_device is made const.
-		 */
-		dev_start = (struct device *)&from->dev;
-	}
+	if (from)
+		dev_start = &from->dev;
 	dev = bus_find_device(&pci_bus_type, dev_start, (void *)id,
 			      match_pci_dev_by_id);
 	if (dev)