| Date | Fri, 1 Aug 2014 20:57:53 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH v3 tip/core/rcu 1/9] rcu: Add call_rcu_tasks() |
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On 07/31, 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)) { > + get_task_struct(t); > + t->rcu_tasks_nvcsw = ACCESS_ONCE(t->nvcsw); > + ACCESS_ONCE(t->rcu_tasks_holdout) = 1; > + list_add(&t->rcu_tasks_holdout_list, > + &rcu_tasks_holdouts); > + } > + } > + rcu_read_unlock();
So let me repeat. for_each_process_thread() above can not (in general) see the exiting tasks which have already called exit_notify(), because such a task can be removed from rcu lists at any time.
Now suppose that proc_exit_connector() is probed. Or another function which can be called after exit_notify(), this doesn't matter.
An exiting task T jumps into trampoline and gets the preemption. It can be already (auto)reaped and removed from rcu lists.
synchronize_rcu_tasks() can not see this task, so it can return before T gets a chance to resume.
Oleg.
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