linux-kernel - Re: [PATCH] kthread: Don't depend on work queues (take 2)

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Message-ID: <20070411192809.GA106@tv-sign.ru>
Date:	Wed, 11 Apr 2007 23:28:09 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Davide Libenzi <davidel@...ilserver.org>,
	Jan Engelhardt <jengelh@...ux01.gwdg.de>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Robin Holt <holt@....com>, Roland McGrath <roland@...hat.com>,
	"Serge E. Hallyn" <serge@...lyn.com>, linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Gautham R Shenoy <ego@...ibm.com>
Subject: Re: [PATCH] kthread: Don't depend on work queues (take 2)

On 04/11, Eric W. Biederman wrote:
> 
> @@ -435,8 +436,12 @@ static void __init setup_command_line(char *command_line)
>  static void noinline rest_init(void)
>  	__releases(kernel_lock)
>  {
> +	int pid;
>  	kernel_thread(init, NULL, CLONE_FS | CLONE_SIGHAND);
>  	numa_default_policy();
> +
> +	pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
> +	kthreadd_task = find_task_by_pid(pid);
>  	unlock_kernel();

Just curious. What if kernel/kthread.c declares

	static struct task_struct *kthreadd_task = &init_task;

an then kthreadd_setup() does kthreadd_task = current. I assume it is always
safe to try_to_wake_up(idle_thread), because it always TASK_RUNNING. This
way we don't need to export kthreadd_task.

> +	spin_lock(&kthread_create_lock);
> +	list_add_tail(&create.list, &kthread_create_list);
> +	wake_up_process(kthreadd_task);
> +	spin_unlock(&kthread_create_lock);

Very minor nit, but we don't need to do wake_up under spin_unlock().

Oleg.

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