[PATCH v4] USB: Fix device driver race

[Bastien Nocera <hadess@hadess.net>]

When a new device with a specialised device driver is plugged in, the
new driver will be modprobe()'d but the driver core will attach the
"generic" driver to the device.

After that, nothing will trigger a reprobe when the modprobe()'d device
driver has finished initialising, as the device has the "generic"
driver attached to it.

Trigger a reprobe ourselves when new specialised drivers get registered.

Fixes: 88b7381a939d
Signed-off-by: Bastien Nocera <hadess@hadess.net>
---

Changes since v3:
- Only reprobe devices that could use the new driver
- Many code fixes

Changes since v2:
- Fix formatting

Changes since v1:
- Simplified after Alan Stern's comments and some clarifications from
Benjamin Tissoires.

 drivers/usb/core/driver.c | 32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index f81606c6a35b..6731a8e104bc 100644
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -905,6 +905,27 @@ static int usb_uevent(struct device *dev, struct kobj_uevent_env *env)
 	return 0;
 }
 
+static int __usb_bus_reprobe_drivers(struct device *dev, void *data)
+{
+	struct usb_device_driver *new_udriver = data;
+	struct usb_device_driver *udriver;
+	struct usb_device *udev;
+
+	if (!dev->driver)
+		return 0;
+
+	udriver = to_usb_device_driver(dev->driver);
+	if (udriver != &usb_generic_driver)
+		return 0;
+
+	udev = to_usb_device(dev);
+	if (usb_device_match_id(udev, new_udriver->id_table) != NULL ||
+	    (new_udriver->match && new_udriver->match(udev) == 0))
+		device_reprobe(dev);
+
+	return 0;
+}
+
 /**
  * usb_register_device_driver - register a USB device (not interface) driver
  * @new_udriver: USB operations for the device driver
@@ -934,13 +955,20 @@ int usb_register_device_driver(struct usb_device_driver *new_udriver,
 
 	retval = driver_register(&new_udriver->drvwrap.driver);
 
-	if (!retval)
+	if (!retval) {
 		pr_info("%s: registered new device driver %s\n",
 			usbcore_name, new_udriver->name);
-	else
+		/* Check whether any device could be better served with
+		 * this new driver
+		 */
+		if (new_udriver->match || new_udriver->id_table)
+			bus_for_each_dev(&usb_bus_type, NULL, new_udriver,
+					 __usb_bus_reprobe_drivers);
+	} else {
 		printk(KERN_ERR "%s: error %d registering device "
 			"	driver %s\n",
 			usbcore_name, retval, new_udriver->name);
+	}
 
 	return retval;
 }