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Sender: Tejun Heo <htejun@gmail.com>
Date: Mon, 10 Oct 2016 08:53:03 -0400
From: Tejun Heo <tj@kernel.org>
To: Balbir Singh <bsingharora@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>, torvalds@linux-foundation.org,
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Subject: Re: Oops on Power8 (was Re: [PATCH v2 1/7] workqueue: make workqueue
 available early during boot)
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On Mon, Oct 10, 2016 at 10:17:16PM +1100, Balbir Singh wrote:
> rest_init()
> {
> 	...
> 	kernel_thread(kernel_init, NULL, CLONE_FS);
> 	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);
> 	...
> 
> }
> 
> create_worker() needs kthreadd, it wakes up kthreadd in kthread_create_on_node,
> workqueue_init() is called from kernel_init() , but kthreadd is created after
> the call to kernel_init(), so its touch and go

But the first thing kernel_init_freeable() does is
wait_for_completion(&kthreadd_done).

Thanks.

-- 
tejun