Re: [RFC PATCH 06/18] signal/kthread: Initial implementation of kthread signal handling

On Mon 2015-06-15 21:14:29, Oleg Nesterov wrote:

Ah, understand. You think that we need to take ->siglock in advance
to avoid the race with SIGCONT?

exactly

No, we don't. Let me show you the code I suggested again:

	void kthread_do_signal_stop(void)
	{
		spin_lock_irq(&curtent->sighand->siglock);
		if (current->jobctl & JOBCTL_STOP_DEQUEUED)
			__set_current_state(TASK_STOPPED);
		spin_unlock_irq(&current->sighand->siglock);

		schedule();
	}
	
so you can dequeue_signal() and call kthread_do_signal_stop() without
holding ->siglock. We can rely on JOBCTL_STOP_DEQUEUED bit. SIGCONT
clears it, so kthread_do_signal_stop() can't race.

Heureka, I have got it. I have previously missed the meaning of the
JOBCTL_STOP_DEQUEUED bit. Thanks for explanation.

Best Regards,
Petr