usb: udc: core: Use lock when write to soft_connect

Use lock to guard against concurrent access for soft-connect/disconnect
operations when writing to soft_connect sysfs.

Fixes: 2ccea03 ("usb: gadget: introduce UDC Class")
Cc: stable@vger.kernel.org
Acked-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Link: https://lore.kernel.org/r/338ea01fbd69b1985ef58f0f59af02c805ddf189.1610611437.git.Thinh.Nguyen@synopsys.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Thinh Nguyen

drivers/usb/gadget/udc/core.c

@@ -1529,10 +1529,13 @@ static ssize_t soft_connect_store(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t n)
 {
 	struct usb_udc		*udc = container_of(dev, struct usb_udc, dev);
+	ssize_t			ret;
 
+	mutex_lock(&udc_lock);
 	if (!udc->driver) {
 		dev_err(dev, "soft-connect without a gadget driver\n");
-		return -EOPNOTSUPP;
+		ret = -EOPNOTSUPP;
+		goto out;
 	}
 
 	if (sysfs_streq(buf, "connect")) {
@@ -1543,10 +1546,14 @@ static ssize_t soft_connect_store(struct device *dev,
 		usb_gadget_udc_stop(udc);
 	} else {
 		dev_err(dev, "unsupported command '%s'\n", buf);
-		return -EINVAL;
+		ret = -EINVAL;
+		goto out;
 	}
 
-	return n;
+	ret = n;
+out:
+	mutex_unlock(&udc_lock);
+	return ret;
 }
 static DEVICE_ATTR_WO(soft_connect);