linux-kernel - Re: [PATCH v2 tip/core/rcu 01/10] rcu: Add call_rcu

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Message-ID: <20140801155310.GA2945@redhat.com>
Date:	Fri, 1 Aug 2014 17:53:10 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, fweisbec@...il.com, bobby.prani@...il.com
Subject: Re: [PATCH v2 tip/core/rcu 01/10] rcu: Add call_rcu_tasks()

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?

Oleg.

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