struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
					   unsigned long *flags)
{
	struct sighand_struct *sighand;

	rcu_read_lock();
	for (;;) {
		sighand = rcu_dereference(tsk->sighand);
		if (unlikely(sighand == NULL))
			break;

		/*
		 * This sighand can be already freed and even reused, but
		 * we rely on SLAB_TYPESAFE_BY_RCU and sighand_ctor() which
		 * initializes ->siglock: this slab can't go away, it has
		 * the same object type, ->siglock can't be reinitialized.
		 *
		 * We need to ensure that tsk->sighand is still the same
		 * after we take the lock, we can race with de_thread() or
		 * __exit_signal(). In the latter case the next iteration
		 * must see ->sighand == NULL.
		 */
		spin_lock_irqsave(&sighand->siglock, *flags);
		if (likely(sighand == rcu_access_pointer(tsk->sighand)))
			break;
		spin_unlock_irqrestore(&sighand->siglock, *flags);
	}
	rcu_read_unlock();

	return sighand;
}