[PATCH] HVC init race

[Hollis Blanchard]

On Nov 3, 2005, at 11:02 PM, Michael Neuling wrote:

> I've been hitting a crash on boot where tty_open is being called 
> before the
> hvc console driver setup is complete.  Below patch fixes this problem.

What is the race exactly? I guess nothing should be calling into 
hvc_open before tty_register_driver()...?

-Hollis

>  drivers/char/hvc_console.c |   32 ++++++++++++++++++--------------
>  1 files changed, 18 insertions(+), 14 deletions(-)
>
> Index: linux-2.6/drivers/char/hvc_console.c
> ===================================================================
> --- linux-2.6.orig/drivers/char/hvc_console.c
> +++ linux-2.6/drivers/char/hvc_console.c
> @@ -823,34 +823,38 @@
>   * interfaces start to become available. */
>  int __init hvc_init(void)
>  {
> +	struct tty_driver *drv;
> +
>  	/* We need more than hvc_count adapters due to hotplug additions. */
> -	hvc_driver = alloc_tty_driver(HVC_ALLOC_TTY_ADAPTERS);
> -	if (!hvc_driver)
> +	drv = alloc_tty_driver(HVC_ALLOC_TTY_ADAPTERS);
> +	if (!drv)
>  		return -ENOMEM;
>
> -	hvc_driver->owner = THIS_MODULE;
> -	hvc_driver->devfs_name = "hvc/";
> -	hvc_driver->driver_name = "hvc";
> -	hvc_driver->name = "hvc";
> -	hvc_driver->major = HVC_MAJOR;
> -	hvc_driver->minor_start = HVC_MINOR;
> -	hvc_driver->type = TTY_DRIVER_TYPE_SYSTEM;
> -	hvc_driver->init_termios = tty_std_termios;
> -	hvc_driver->flags = TTY_DRIVER_REAL_RAW;
> -	tty_set_operations(hvc_driver, &hvc_ops);
> +	drv->owner = THIS_MODULE;
> +	drv->devfs_name = "hvc/";
> +	drv->driver_name = "hvc";
> +	drv->name = "hvc";
> +	drv->major = HVC_MAJOR;
> +	drv->minor_start = HVC_MINOR;
> +	drv->type = TTY_DRIVER_TYPE_SYSTEM;
> +	drv->init_termios = tty_std_termios;
> +	drv->flags = TTY_DRIVER_REAL_RAW;
> +	tty_set_operations(drv, &hvc_ops);
>
>  	/* Always start the kthread because there can be hotplug vty adapters
>  	 * added later. */
>  	hvc_task = kthread_run(khvcd, NULL, "khvcd");
>  	if (IS_ERR(hvc_task)) {
>  		panic("Couldn't create kthread for console.\n");
> -		put_tty_driver(hvc_driver);
> +		put_tty_driver(drv);
>  		return -EIO;
>  	}
>
> -	if (tty_register_driver(hvc_driver))
> +	if (tty_register_driver(drv))
>  		panic("Couldn't register hvc console driver\n");
>
> +	mb();
> +	hvc_driver = drv;
>  	return 0;
>  }
>  module_init(hvc_init);
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