linux-kernel - Re: [PATCH 2/3] make kthread

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Message-Id: <20070413143104.99a1eeb9.akpm@linux-foundation.org>
Date:	Fri, 13 Apr 2007 14:31:04 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Davide Libenzi <davidel@...ilserver.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Roland McGrath <roland@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] make kthread_create() more scalable

On Fri, 13 Apr 2007 17:02:01 +0400
Oleg Nesterov <oleg@...sign.ru> wrote:

> If kernel_thread(kthread) succeeds, kthread() can not fail on its path to
> complete(&create->started) + schedule(). After that it can't be woken because
> nobody can see the new task yet. This means:
> 
> 	- we don't need tasklist_lock for find_task_by_pid().
> 
> 	- create_kthread() doesn't need to wait for create->started. Instead,
> 	  kthread_create() first waits for create->created to get the result of
> 	  kernel_thread(), then waits for create->started to synchronize with
> 	  kthread().

Why don't we need tasklist_lock for find_task_by_pid()?  I'd have though that
we'd at least need rcu_read_lock(), and I'm not sure that the implicit
understanding of pid-management internals here is a great idea.
-
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