Re: [PATCH v2 tip/core/rcu 01/10] rcu: Add call_rcu_tasks()

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Fri, Aug 01, 2014 at 05:53:10PM +0200, Oleg Nesterov wrote:
> On 07/30, Paul E. McKenney wrote:
> >
> > +		rcu_read_lock();
> > +		for_each_process_thread(g, t) {
> > +			if (t != current && ACCESS_ONCE(t->on_rq) &&
> > +			    !is_idle_task(t)) {
> > +				t->rcu_tasks_nvcsw = ACCESS_ONCE(t->nvcsw);
> > +				t->rcu_tasks_holdout = 1;
> > +				list_add(&t->rcu_tasks_holdout_list,
> > +					 &rcu_tasks_holdouts);
> > +			}
> > +		}
> > +		rcu_read_unlock();
> 
> Wait, unless I missed something this can't work...
> 
> The problem is, once the exiting task passes exit_notify() it can
> be removed from rcu lists.
> 
> Now suppose that (say) proc_exit_connector() has a probe, and this
> task has jumped into trampoline and it was preempted there.
> 
> No?

OK, this sounds to me like another vote for get_task_struct() as used
in the v3 series.  Or am I missing something?

							Thanx, Paul