PCI: Catch attempts to disable already-disabled devices

Warn when disabling a device that has already been disabled.

[bhelgaas: message wording]
Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/pci/pci.c

@@ -1401,6 +1401,9 @@ pci_disable_device(struct pci_dev *dev)
 	if (dr)
 		dr->enabled = 0;
 
+	dev_WARN_ONCE(&dev->dev, atomic_read(&dev->enable_cnt) <= 0,
+		      "disabling already-disabled device");
+
 	if (atomic_sub_return(1, &dev->enable_cnt) != 0)
 		return;