uio: Request/free irq separate from dev lifecycle

Separate irq request/free from the device lifecycle.
After device unregister the parent module can call pci_disable_msi.
>From the PCI MSI how to:

"Before calling this function, a device driver must always call free_irq()
on any interrupt for which it previously called request_irq().
Failure to do so results in a BUG_ON(), leaving the device with
MSI enabled and thus leaking its vector."

So we need to separately free the irq at unregister to allow the device
to be kept around in the case of it still having open FDs.
Signed-off-by: Brian Russell <brussell@brocade.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/uio/uio.c

@@ -835,7 +835,15 @@ int __uio_register_device(struct module *owner,
 	info->uio_dev = idev;
 
 	if (info->irq && (info->irq != UIO_IRQ_CUSTOM)) {
-		ret = devm_request_irq(idev->dev, info->irq, uio_interrupt,
+		/*
+		 * Note that we deliberately don't use devm_request_irq
+		 * here. The parent module can unregister the UIO device
+		 * and call pci_disable_msi, which requires that this
+		 * irq has been freed. However, the device may have open
+		 * FDs at the time of unregister and therefore may not be
+		 * freed until they are released.
+		 */
+		ret = request_irq(info->irq, uio_interrupt,
 				  info->irq_flags, info->name, idev);
 		if (ret)
 			goto err_request_irq;
@@ -871,6 +879,8 @@ void uio_unregister_device(struct uio_info *info)
 
 	uio_dev_del_attributes(idev);
 
+	free_irq(idev->info->irq, idev);
+
 	device_destroy(&uio_class, MKDEV(uio_major, idev->minor));
 
 	return;