static int
pinspect_enable(struct proc *p, struct lwp *l)
{
	struct lwp *lt;
	struct cpu_info *ci;
	int s;
	int error = 0;
	u_int ipi_id;

	KASSERT(l == curlwp);

	if ((ipi_id = ipi_register(pinspect_ipi, NULL)) == 0)
		return ENOMEM;

	s = splhigh();
	kpreempt_disable();
	mutex_enter(p->p_lock);
	if (ISSET(p->p_sflag, PS_INSPECTING)) {
		error = EBUSY;
		goto err;
	}

	KASSERT(!ISSET(l->l_pflag, LP_INSPECTOR));

	SET(p->p_sflag, PS_INSPECTING);
	SET(l->l_pflag, LP_INSPECTOR);

	/*
	 * Send IPI to all other LWPs running on CPU,
	 * so they will return to the kernel and block
	 * in userret().
	 */
	LIST_FOREACH(lt, &p->p_lwps, l_sibling) {
		/* Do not inspect self */
		if (lt == l)
			continue;

		lwp_lock(lt);
		if (lt->l_stat == LSONPROC) {
			ci = lwp_getcpu(lt);
			ipi_trigger(ipi_id, ci);
		}
		lwp_unlock(lt);
	}

err:
	mutex_exit(p->p_lock);
	kpreempt_enable();
	splx(s);

	ipi_unregister(ipi_id);

	return error;
}