diff --git a/Documentation/ABI/testing/configfs-usb-gadget-loopback b/Documentation/ABI/testing/configfs-usb-gadget-loopback
new file mode 100644
index 000000000000..852b2365a5b5
--- /dev/null
+++ b/Documentation/ABI/testing/configfs-usb-gadget-loopback
@@ -0,0 +1,8 @@
+What:		/config/usb-gadget/gadget/functions/Loopback.name
+Date:		Nov 2013
+KenelVersion:	3.13
+Description:
+		The attributes:
+
+		qlen		- depth of loopback queue
+		bulk_buflen	- buffer length
diff --git a/drivers/usb/gadget/Kconfig b/drivers/usb/gadget/Kconfig
index a91e6422f930..26fe8769be45 100644
--- a/drivers/usb/gadget/Kconfig
+++ b/drivers/usb/gadget/Kconfig
@@ -689,6 +689,18 @@ config USB_CONFIGFS_MASS_STORAGE
 	  device (in much the same way as the "loop" device driver),
 	  specified as a module parameter or sysfs option.
 
+config USB_CONFIGFS_F_LB
+	boolean "Loopback function (for testing)"
+	depends on USB_CONFIGFS
+	select USB_F_SS_LB
+	help
+	  It loops back a configurable number of transfers.
+	  It also implements control requests, for "chapter 9" conformance.
+	  Make this be the first driver you try using on top of any new
+	  USB peripheral controller driver.  Then you can use host-side
+	  test software, like the "usbtest" driver, to put your hardware
+	  and its driver through a basic set of functional tests.
+
 config USB_ZERO
 	tristate "Gadget Zero (DEVELOPMENT)"
 	select USB_LIBCOMPOSITE
diff --git a/drivers/usb/gadget/f_loopback.c b/drivers/usb/gadget/f_loopback.c
index b79065376a16..c35bb40cabf2 100644
--- a/drivers/usb/gadget/f_loopback.c
+++ b/drivers/usb/gadget/f_loopback.c
@@ -231,6 +231,14 @@ autoconf_fail:
 
 static void lb_free_func(struct usb_function *f)
 {
+	struct f_lb_opts *opts;
+
+	opts = container_of(f->fi, struct f_lb_opts, func_inst);
+
+	mutex_lock(&opts->lock);
+	opts->refcnt--;
+	mutex_unlock(&opts->lock);
+
 	usb_free_all_descriptors(f);
 	kfree(func_to_loop(f));
 }
@@ -386,6 +394,11 @@ static struct usb_function *loopback_alloc(struct usb_function_instance *fi)
 		return ERR_PTR(-ENOMEM);
 
 	lb_opts = container_of(fi, struct f_lb_opts, func_inst);
+
+	mutex_lock(&lb_opts->lock);
+	lb_opts->refcnt++;
+	mutex_unlock(&lb_opts->lock);
+
 	buflen = lb_opts->bulk_buflen;
 	qlen = lb_opts->qlen;
 	if (!qlen)
@@ -402,6 +415,118 @@ static struct usb_function *loopback_alloc(struct usb_function_instance *fi)
 	return &loop->function;
 }
 
+static inline struct f_lb_opts *to_f_lb_opts(struct config_item *item)
+{
+	return container_of(to_config_group(item), struct f_lb_opts,
+			    func_inst.group);
+}
+
+CONFIGFS_ATTR_STRUCT(f_lb_opts);
+CONFIGFS_ATTR_OPS(f_lb_opts);
+
+static void lb_attr_release(struct config_item *item)
+{
+	struct f_lb_opts *lb_opts = to_f_lb_opts(item);
+
+	usb_put_function_instance(&lb_opts->func_inst);
+}
+
+static struct configfs_item_operations lb_item_ops = {
+	.release		= lb_attr_release,
+	.show_attribute		= f_lb_opts_attr_show,
+	.store_attribute	= f_lb_opts_attr_store,
+};
+
+static ssize_t f_lb_opts_qlen_show(struct f_lb_opts *opts, char *page)
+{
+	int result;
+
+	mutex_lock(&opts->lock);
+	result = sprintf(page, "%d", opts->qlen);
+	mutex_unlock(&opts->lock);
+
+	return result;
+}
+
+static ssize_t f_lb_opts_qlen_store(struct f_lb_opts *opts,
+				    const char *page, size_t len)
+{
+	int ret;
+	u32 num;
+
+	mutex_lock(&opts->lock);
+	if (opts->refcnt) {
+		ret = -EBUSY;
+		goto end;
+	}
+
+	ret = kstrtou32(page, 0, &num);
+	if (ret)
+		goto end;
+
+	opts->qlen = num;
+	ret = len;
+end:
+	mutex_unlock(&opts->lock);
+	return ret;
+}
+
+static struct f_lb_opts_attribute f_lb_opts_qlen =
+	__CONFIGFS_ATTR(qlen, S_IRUGO | S_IWUSR,
+			f_lb_opts_qlen_show,
+			f_lb_opts_qlen_store);
+
+static ssize_t f_lb_opts_bulk_buflen_show(struct f_lb_opts *opts, char *page)
+{
+	int result;
+
+	mutex_lock(&opts->lock);
+	result = sprintf(page, "%d", opts->bulk_buflen);
+	mutex_unlock(&opts->lock);
+
+	return result;
+}
+
+static ssize_t f_lb_opts_bulk_buflen_store(struct f_lb_opts *opts,
+				    const char *page, size_t len)
+{
+	int ret;
+	u32 num;
+
+	mutex_lock(&opts->lock);
+	if (opts->refcnt) {
+		ret = -EBUSY;
+		goto end;
+	}
+
+	ret = kstrtou32(page, 0, &num);
+	if (ret)
+		goto end;
+
+	opts->bulk_buflen = num;
+	ret = len;
+end:
+	mutex_unlock(&opts->lock);
+	return ret;
+}
+
+static struct f_lb_opts_attribute f_lb_opts_bulk_buflen =
+	__CONFIGFS_ATTR(buflen, S_IRUGO | S_IWUSR,
+			f_lb_opts_bulk_buflen_show,
+			f_lb_opts_bulk_buflen_store);
+
+static struct configfs_attribute *lb_attrs[] = {
+	&f_lb_opts_qlen.attr,
+	&f_lb_opts_bulk_buflen.attr,
+	NULL,
+};
+
+static struct config_item_type lb_func_type = {
+	.ct_item_ops    = &lb_item_ops,
+	.ct_attrs	= lb_attrs,
+	.ct_owner       = THIS_MODULE,
+};
+
 static void lb_free_instance(struct usb_function_instance *fi)
 {
 	struct f_lb_opts *lb_opts;
@@ -417,7 +542,14 @@ static struct usb_function_instance *loopback_alloc_instance(void)
 	lb_opts = kzalloc(sizeof(*lb_opts), GFP_KERNEL);
 	if (!lb_opts)
 		return ERR_PTR(-ENOMEM);
+	mutex_init(&lb_opts->lock);
 	lb_opts->func_inst.free_func_inst = lb_free_instance;
+	lb_opts->bulk_buflen = GZERO_BULK_BUFLEN;
+	lb_opts->qlen = GZERO_QLEN;
+
+	config_group_init_type_name(&lb_opts->func_inst.group, "",
+				    &lb_func_type);
+
 	return  &lb_opts->func_inst;
 }
 DECLARE_USB_FUNCTION(Loopback, loopback_alloc_instance, loopback_alloc);
diff --git a/drivers/usb/gadget/g_zero.h b/drivers/usb/gadget/g_zero.h
index a1c1a978b5e9..19ec50a42a74 100644
--- a/drivers/usb/gadget/g_zero.h
+++ b/drivers/usb/gadget/g_zero.h
@@ -6,6 +6,9 @@
 #ifndef __G_ZERO_H
 #define __G_ZERO_H
 
+#define GZERO_BULK_BUFLEN	4096
+#define GZERO_QLEN		32
+
 struct usb_zero_options {
 	unsigned pattern;
 	unsigned isoc_interval;
@@ -30,6 +33,15 @@ struct f_lb_opts {
 	struct usb_function_instance func_inst;
 	unsigned bulk_buflen;
 	unsigned qlen;
+
+	/*
+	 * Read/write access to configfs attributes is handled by configfs.
+	 *
+	 * This is to protect the data from concurrent access by read/write
+	 * and create symlink/remove symlink.
+	 */
+	struct mutex			lock;
+	int				refcnt;
 };
 
 void lb_modexit(void);
diff --git a/drivers/usb/gadget/zero.c b/drivers/usb/gadget/zero.c
index 0dd07ae1555d..d954bba7b405 100644
--- a/drivers/usb/gadget/zero.c
+++ b/drivers/usb/gadget/zero.c
@@ -66,8 +66,8 @@ module_param(loopdefault, bool, S_IRUGO|S_IWUSR);
 static struct usb_zero_options gzero_options = {
 	.isoc_interval = 4,
 	.isoc_maxpacket = 1024,
-	.bulk_buflen = 4096,
-	.qlen = 32,
+	.bulk_buflen = GZERO_BULK_BUFLEN,
+	.qlen = GZERO_QLEN,
 };
 
 /*-------------------------------------------------------------------------*/