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

[Oleg Nesterov <oleg@redhat.com>]

On 08/01, Paul E. McKenney wrote:
>
> 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?

Ah. Sorry for confusion, I replied to the wrong email, let me resend...

Oleg.