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

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Date:	Mon, 11 Feb 2013 15:10:38 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Haojian Zhuang <haojian.zhuang@...aro.org>
Cc:	gregkh@...uxfoundation.org, viro@...iv.linux.org.uk,
	rusty@...tcorp.com.au, hpa@...ux.intel.com, jim.cromie@...il.com,
	linux-kernel@...r.kernel.org, linux@....linux.org.uk,
	linus.walleij@...aro.org, grant.likely@...retlab.ca, arnd@...db.de,
	broonie@...nsource.wolfsonmicro.com, patches@...aro.org
Subject: Re: [PATCH] driver core: add wait event for deferred probe

On Sun, 10 Feb 2013 00:57:57 +0800
Haojian Zhuang <haojian.zhuang@...aro.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.
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