Re: [PATCH] driver core: add wait event for deferred probe

[Andrew Morton <akpm@linux-foundation.org>]

On Sun, 10 Feb 2013 00:57:57 +0800
Haojian Zhuang <haojian.zhuang@linaro.org> wrote:

> do_initcalls() could call all driver initialization code in kernel_init
> thread. It means that probe() function will be also called from that
> time. After this, kernel could access console & release __init section
> in the same thread.
> 
> But if device probe fails and moves into deferred probe list, a new
> thread is created to reinvoke probe. If the device is serial console,
> kernel has to open console failure & release __init section before
> reinvoking failure. Because there's no synchronization mechanism.
> Now add wait event to synchronize after do_initcalls().

It sounds like this:

static int __ref kernel_init(void *unused)
{
	kernel_init_freeable();
	/* need to finish all async __init code before freeing the memory */
	async_synchronize_full();

is designed to prevent the problem you describe?

> --- a/init/main.c
> +++ b/init/main.c
> @@ -786,6 +786,7 @@ static void __init do_basic_setup(void)
>  	do_ctors();
>  	usermodehelper_enable();
>  	do_initcalls();
> +	wait_for_device_probe();
>  }

Needs a nice comment here explaining what's going on.