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

On 10/10/16 23:53, Tejun Heo wrote:

On Mon, Oct 10, 2016 at 10:17:16PM +1100, Balbir Singh wrote:

quoted

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).

Yes, Of course, looking at the stack trace again, it was not the wake_up itself,
but the absence of cfs_rq of p->se that caused the issue. Will try and chase it
down. Quick look shows cgroup_init() has occurred before workqueue_init(), so
ideally p->se.cfs_rq should be allocated.

Sorry for the noise,

Balbir