driver core: platform: fix race condition with driver_override

The driver_override implementation is susceptible to race condition when
different threads are reading vs storing a different driver override.
Add locking to avoid race condition.

Fixes: 3d713e0e382e ("driver core: platform: add device binding path 'driver_override'")
Cc: stable@vger.kernel.org
Signed-off-by: Adrian Salido <salidoa@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
void __init early_platform_driver_register_all(char *class_str)
{
	/* The "class_str" parameter may or may not be present on the kernel
	 * command line. If it is present then there may be more than one
	 * matching parameter.
	 *
	 * Since we register our early platform drivers using early_param()
	 * we need to make sure that they also get registered in the case
	 * when the parameter is missing from the kernel command line.
	 *
	 * We use parse_early_options() to make sure the early_param() gets
	 * called at least once. The early_param() may be called more than
	 * once since the name of the preferred device may be specified on
	 * the kernel command line. early_platform_driver_register() handles
	 * this case for us.
	 */
	parse_early_options(class_str);
}

void __init early_platform_driver_register_all(char *class_str)
{
	/* The "class_str" parameter may or may not be present on the kernel
	 * command line. If it is present then there may be more than one
	 * matching parameter.
	 *
	 * Since we register our early platform drivers using early_param()
	 * we need to make sure that they also get registered in the case
	 * when the parameter is missing from the kernel command line.
	 *
	 * We use parse_early_options() to make sure the early_param() gets
	 * called at least once. The early_param() may be called more than
	 * once since the name of the preferred device may be specified on
	 * the kernel command line. early_platform_driver_register() handles
	 * this case for us.
	 */
	parse_early_options(class_str);
}
