linux-kernel - Re: Oops on Power8 (was Re: [PATCH v2 1/7] workqueue: make workqueue available early during boot)

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Date:   Mon, 10 Oct 2016 08:53:03 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Balbir Singh <bsingharora@...il.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        torvalds@...ux-foundation.org, linuxppc-dev@...ts.ozlabs.org,
        akpm@...ux-foundation.org, kernel-team@...com,
        jiangshanlai@...il.com, linux-kernel@...r.kernel.org
Subject: Re: Oops on Power8 (was Re: [PATCH v2 1/7] workqueue: make workqueue
 available early during boot)

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