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

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Message-ID: <m18xcvonl5.fsf@ebiederm.dsl.xmission.com>
Date:	Fri, 13 Apr 2007 17:34:46 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Davide Libenzi <davidel@...ilserver.org>,
	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

Oleg Nesterov <oleg@...sign.ru> writes:

> 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().

Well we do need rcu_read_lock();
But if we are going to wait until the thread has run we can just pass
back current.

> 	- 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().

We can do even better.  We only need a single completion. 
If it was an error create_create can complete it.
Otherwise kthread() can complete it.

Patch in a bit as soon as I finish testing...


Eric
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