linux-kernel - Re: [PATCH 0/1] kthreads: simplify !kthreadd_task logic, kill kthreadd_task_init

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Date:	Fri, 18 Sep 2009 20:54:25 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Wu Fei <at.wufei@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>, arjan@...radead.org,
	jeremy@...p.org, mschmidt@...hat.com, mingo@...hat.com,
	hpa@...or.com, linux-kernel@...r.kernel.org, tj@...nel.org,
	tglx@...utronix.de, Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-tip-commits@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 0/1] kthreads: simplify !kthreadd_task logic, kill
	kthreadd_task_init_done

On 09/19, Wu Fei wrote:
>
> On Fri, Sep 04, 2009 at 09:37:49AM +0200, Ingo Molnar wrote:
> >
> > Lets delay this until i can debug it more fully.
> >
> CONFIG_PREEMPT_VOLUNTARY looks like the key of this problem,
> might_resched becomes _cond_resched, and since d86ee480 changes
> it not to check SYSTEM_RUNNING,

... and should_resched() is true under preempt_disable()

> --- a/init/main.c
> +++ b/init/main.c
> @@ -452,10 +452,10 @@ static noinline void __init_refok rest_init(void)
>  	int pid;
>
>  	rcu_scheduler_starting();
> -	kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
> -	numa_default_policy();
>  	pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
>  	kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
> +	kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);

We can't do this. kernel_init() should run with ->pid == 1, we are
going to exec /sbin/init.

Oleg.

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