Subject: Re: [PATCH v3 1/3] init / kthread: add module_long_probe_init() and module_long_probe_exit()

From: Oleg Nesterov <[email-masked]>
Date: Wed, 13 Aug 2014 19:51:01 +0200

On 08/12, Luis R. Rodriguez wrote:
>
> +/* To be used by modules which can take over 30 seconds at probe */

Probably the comment should explain that this hack should only be
used if the driver is buggy and is wating for "real fix".

> +#define module_long_probe_init(initfn)				\
> +	static struct task_struct *__init_thread;		\
> +	static int _long_probe_##initfn(void *arg)		\
> +	{							\
> +		return initfn();				\
> +	}							\
> +	static inline __init int __long_probe_##initfn(void)	\
> +	{							\
> +		__init_thread = kthread_run(_long_probe_##initfn,\
> +					    NULL,		\
> +					    #initfn);		\
> +		if (IS_ERR(__init_thread))			\
> +			return PTR_ERR(__init_thread);		\
> +		return 0;					\
> +	}							\
> +	module_init(__long_probe_##initfn);
> +/* To be used by modules that require module_long_probe_init() */
> +#define module_long_probe_exit(exitfn)				\
> +	static inline void __long_probe_##exitfn(void)		\
> +	{							\
> +		exitfn();					\
> +		if (__init_thread)				\
> +			kthread_stop(__init_thread);		\
> +	}							\

exitfn() should be called after kthread_stop(), and only if initfn()
returns 0. So it should probably do

	int err = kthread_stop(__init_thread);
	if (!err)
		exitfn();

But there is an additional complication, you can't use __init_thread
without get_task_struct(), so  __long_probe_##initfn() can't use
kthread_run(). It needs kthread_create() + get_task_struct() + wakeup.

Oleg.