struct tty_driver *__tty_alloc_driver(unsigned int lines, struct module *owner,
		unsigned long flags)
{
	struct tty_driver *driver;
	unsigned int cdevs = 1;
	int err;

	if (!lines || (flags & TTY_DRIVER_UNNUMBERED_NODE && lines > 1))
		return ERR_PTR(-EINVAL);

	driver = kzalloc(sizeof(struct tty_driver), GFP_KERNEL);
	if (!driver)
		return ERR_PTR(-ENOMEM);

	kref_init(&driver->kref);
	driver->magic = TTY_DRIVER_MAGIC;
	driver->num = lines;
	driver->owner = owner;
	driver->flags = flags;

	if (!(flags & TTY_DRIVER_DEVPTS_MEM)) {
		driver->ttys = kcalloc(lines, sizeof(*driver->ttys),
				GFP_KERNEL);
		driver->termios = kcalloc(lines, sizeof(*driver->termios),
				GFP_KERNEL);
		if (!driver->ttys || !driver->termios) {
			err = -ENOMEM;
			goto err_free_all;
		}
	}

	if (!(flags & TTY_DRIVER_DYNAMIC_ALLOC)) {
		driver->ports = kcalloc(lines, sizeof(*driver->ports),
				GFP_KERNEL);
		if (!driver->ports) {
			err = -ENOMEM;
			goto err_free_all;
		}
		cdevs = lines;
	}

	driver->cdevs = kcalloc(cdevs, sizeof(*driver->cdevs), GFP_KERNEL);
	if (!driver->cdevs) {
		err = -ENOMEM;
		goto err_free_all;
	}

	return driver;
err_free_all:
	kfree(driver->ports);
	kfree(driver->ttys);
	kfree(driver->termios);
	kfree(driver->cdevs);
	kfree(driver);
	return ERR_PTR(err);
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.