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From: Ingo Molnar on 28 Jun 2010 10:20

* Peter Zijlstra <peterz(a)infradead.org> wrote:

> +static __initdata DEFINE_MUTEX(kthreadd_lock);

> + /*
> + * We need to spawn init first so that it obtains pid-1, however
> + * the init task will end up wanting to create kthreads, which
> + * if we schedule it before we create kthreadd, will OOPS.
> + */
> + mutex_lock(&kthreadd_lock);
> kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
> numa_default_policy();
> pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
> rcu_read_lock();
> kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
> rcu_read_unlock();
> + mutex_unlock(&kthreadd_lock);
> unlock_kernel();
>
> /*
> @@ -847,6 +856,13 @@ static noinline int init_post(void)
>
> static int __init kernel_init(void * unused)
> {
> + /*
> + * We spawned this thread while holding this lock, ensure the
> + * locked section in rest_init() is complete before proceeding.
> + */
> + mutex_lock(&kthreadd_lock);
> + mutex_unlock(&kthreadd_lock);

I think you may be using a mutex as a completion in essence. Why not use
completions instead?

Ingo
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From: Ilya Loginov on 28 Jun 2010 16:10
On Mon, 28 Jun 2010 13:53:17 +0200
Peter Zijlstra <peterz(a)infradead.org> wrote:

> I just realized its all __init code so its all 'free' anyway, how about
> the nicer version:

I will try both versions and write about results. But I think, that there is
some logical inconsistent in these patches (for me). I like v2 more than v1.
But, I would move mutex_lock/unlock. Anyway, I will try your patches first.

Many thanks.

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Ilya Loginov <isloginov(a)gmail.com>
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