driver core: fix bus_rescan_devices() race.

[PATCH] driver core: fix bus_rescan_devices() race.

bus_rescan_devices_helper() does not hold the dev->sem when it checks for !dev->driver. device_attach() holds the sem, but calls again device_bind_driver() even when dev->driver is set (which means device is already bound to a driver). what happens is that a first device_attach() call (module insertion time) is on the way binding the device to a driver. another thread calls bus_rescan_devices(). now when bus_rescan_devices_helper() checks for dev->driver it is still NULL 'cos the the prior device_attach() is not yet finished. but as soon as the first one releases the dev->sem the second device_attach() tries to rebind the already bound device again. device_bind_driver() does this blindly which leads to a corrupt driver->klist_devices list (the device links itself, the head points to the device). later a call to device_release_driver() sets dev->driver to NULL and breaks the link it has to itself on knode_driver. rmmoding the driver later calls driver_detach() which leads to an endless loop 'cos the list head in klist_devices still points to the device. and since dev->driver is NULL it's stuck with the same device forever. boom. and rmmod hangs.

very easy to reproduce with new-style pcmcia and a 16bit card. just loop modprobe <pcmcia-modules> ;cardctl eject; rmmod <card driver, pcmcia modules>.

fix is not to call device_bind_driver() in device_attach() if dev->driver is non-NULL. this is wrong anyway since if dev->driver is set the device is bound. also remove the dev->drv check in bus_rescan_devices_helper().

and while at it replace spin_(un|)lock_irq in driver_detach with the non-irq variants. just doesn't make sense to me. the whole klist locking never uses the irq variants.

@@ -127,10 +127,9 @@ int device_attach(struct device * dev)
 	int ret = 0;
 
 	down(&dev->sem);
-	if (dev->driver) {
-		device_bind_driver(dev);
+	if (dev->driver)
 		ret = 1;
-	} else
+	else
 		ret = bus_for_each_drv(dev->bus, NULL, dev, __device_attach);
 	up(&dev->sem);
 	return ret;

@@ -222,15 +221,15 @@ void driver_detach(struct device_driver 
 	struct device * dev;
 
 	for (;;) {
-		spin_lock_irq(&drv->klist_devices.k_lock);
+		spin_lock(&drv->klist_devices.k_lock);
 		if (list_empty(&drv->klist_devices.k_list)) {
-			spin_unlock_irq(&drv->klist_devices.k_lock);
+			spin_unlock(&drv->klist_devices.k_lock);
 			break;
 		}
 		dev = list_entry(drv->klist_devices.k_list.prev,
 				struct device, knode_driver.n_node);
 		get_device(dev);
-		spin_unlock_irq(&drv->klist_devices.k_lock);
+		spin_unlock(&drv->klist_devices.k_lock);
 
 		down(&dev->sem);
 		if (dev->driver == drv)

@@ -485,8 +485,7 @@ void bus_remove_driver(struct device_dri
 /* Helper for bus_rescan_devices's iter */
 static int bus_rescan_devices_helper(struct device *dev, void *data)
 {
-	if (!dev->driver)
-		device_attach(dev);
+	device_attach(dev);
 	return 0;
 }