USB: create a new thread for every USB device found during the probe sequence

Might speed up some systems.  If nothing else, a bad driver should not
take the whole USB subsystem down with it.
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/core/Kconfig

@@ -72,6 +72,21 @@ config USB_SUSPEND
 
 	  If you are unsure about this, say N here.
 
+config USB_MULTITHREAD_PROBE
+	bool "USB Multi-threaded probe (EXPERIMENTAL)"
+	depends on USB && EXPERIMENTAL
+	default n
+	help
+	  Say Y here if you want the USB core to spawn a new thread for
+	  every USB device that is probed.  This can cause a small speedup
+	  in boot times on systems with a lot of different USB devices.
+
+	  This option should be safe to enable, but if any odd probing
+	  problems are found, please disable it, or dynamically turn it
+	  off in the /sys/module/usbcore/parameters/multithread_probe
+	  file
+
+	  When in doubt, say N.
 
 config USB_OTG
 	bool

drivers/usb/core/hub.c

@@ -87,6 +87,16 @@ static DECLARE_WAIT_QUEUE_HEAD(khubd_wait);
 
 static struct task_struct *khubd_task;
 
+/* multithreaded probe logic */
+static int multithread_probe =
+#ifdef CONFIG_USB_MULTITHREAD_PROBE
+	1;
+#else
+	0;
+#endif
+module_param(multithread_probe, bool, S_IRUGO);
+MODULE_PARM_DESC(multithread_probe, "Run each USB device probe in a new thread");
+
 /* cycle leds on hubs that aren't blinking for attention */
 static int blinkenlights = 0;
 module_param (blinkenlights, bool, S_IRUGO);
@@ -1238,29 +1248,17 @@ static inline void show_string(struct usb_device *udev, char *id, char *string)
 static int __usb_port_suspend(struct usb_device *, int port1);
 #endif
 
-/**
- * usb_new_device - perform initial device setup (usbcore-internal)
- * @udev: newly addressed device (in ADDRESS state)
- *
- * This is called with devices which have been enumerated, but not yet
- * configured.  The device descriptor is available, but not descriptors
- * for any device configuration.  The caller must have locked either
- * the parent hub (if udev is a normal device) or else the
- * usb_bus_list_lock (if udev is a root hub).  The parent's pointer to
- * udev has already been installed, but udev is not yet visible through
- * sysfs or other filesystem code.
- *
- * Returns 0 for success (device is configured and listed, with its
- * interfaces, in sysfs); else a negative errno value.
- *
- * This call is synchronous, and may not be used in an interrupt context.
- *
- * Only the hub driver or root-hub registrar should ever call this.
- */
-int usb_new_device(struct usb_device *udev)
+static int __usb_new_device(void *void_data)
 {
+	struct usb_device *udev = void_data;
 	int err;
 
+	/* Lock ourself into memory in order to keep a probe sequence
+	 * sleeping in a new thread from allowing us to be unloaded.
+	 */
+	if (!try_module_get(THIS_MODULE))
+		return -EINVAL;
+
 	err = usb_get_configuration(udev);
 	if (err < 0) {
 		dev_err(&udev->dev, "can't read configurations, error %d\n",
@@ -1356,13 +1354,52 @@ int usb_new_device(struct usb_device *udev)
 		goto fail;
 	}
 
-	return 0;
+exit:
+	module_put(THIS_MODULE);
+	return err;
 
 fail:
 	usb_set_device_state(udev, USB_STATE_NOTATTACHED);
-	return err;
+	goto exit;
 }
 
+/**
+ * usb_new_device - perform initial device setup (usbcore-internal)
+ * @udev: newly addressed device (in ADDRESS state)
+ *
+ * This is called with devices which have been enumerated, but not yet
+ * configured.  The device descriptor is available, but not descriptors
+ * for any device configuration.  The caller must have locked either
+ * the parent hub (if udev is a normal device) or else the
+ * usb_bus_list_lock (if udev is a root hub).  The parent's pointer to
+ * udev has already been installed, but udev is not yet visible through
+ * sysfs or other filesystem code.
+ *
+ * The return value for this function depends on if the
+ * multithread_probe variable is set or not.  If it's set, it will
+ * return a if the probe thread was successfully created or not.  If the
+ * variable is not set, it will return if the device is configured
+ * properly or not.  interfaces, in sysfs); else a negative errno value.
+ *
+ * This call is synchronous, and may not be used in an interrupt context.
+ *
+ * Only the hub driver or root-hub registrar should ever call this.
+ */
+int usb_new_device(struct usb_device *udev)
+{
+	struct task_struct *probe_task;
+	int ret = 0;
+
+	if (multithread_probe) {
+		probe_task = kthread_run(__usb_new_device, udev,
+					 "usb-probe-%s", udev->devnum);
+		if (IS_ERR(probe_task))
+			ret = PTR_ERR(probe_task);
+	} else
+		ret = __usb_new_device(udev);
+
+	return ret;
+}
 
 static int hub_port_status(struct usb_hub *hub, int port1,
 			       u16 *status, u16 *change)