Re: keventd_create_kthread

[Andrew Morton <akpm@osdl.org>]

Srivatsa Vaddagiri <vatsa@in.ibm.com> wrote:
>
> On Thu, Feb 19, 2004 at 08:12:19AM +0000, Andrew Morton wrote:
> > However, if that wake_up_process() comes too early we'll just flip the new
> > thread out of TASK_INTERUPTIBLE into TASK_RUNNING and the schedule() in
> > kthread() will fall straight through.  So perhaps we can simply remove the
> > wait_task_inactive()?
> 
> If wake_up_process() comes too early (when the target task is still
> in TASK_RUNNING state), then won't wake_up_process() be a no-op?
> In which case, the target kthread will miss a wake-up event 
> (kthread_start/kthread_stop)?

No, that's OK - the new kernel thread sets TASK_INTERRUPTIBLE before waking
the invoking thread via complete():

new thread:

	/* OK, tell user we're spawned, wait for stop or wakeup */
	__set_current_state(TASK_INTERRUPTIBLE);
	complete(&create->started);
	schedule();

invoker:

	wait_for_completion(&create->started);
	create->result = find_task_by_pid(pid);
	wait_task_inactive(create->result);

It's the window after the complete() and before the schedule() where
wait_task_inactive() is spinning.