linux-kernel - Re: [PATCH RFC tip/core/rcu 1/9] rcu: Add call_rcu

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Date:	Wed, 30 Jul 2014 14:52:41 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
CC:	<linux-kernel@...r.kernel.org>, <mingo@...nel.org>,
	<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>, <oleg@...hat.com>, <bobby.prani@...il.com>
Subject: Re: [PATCH RFC tip/core/rcu 1/9] rcu: Add call_rcu_tasks()

On 07/29/2014 06:56 AM, Paul E. McKenney wrote:

> +		/*
> +		 * Each pass through the following loop scans the list
> +		 * of holdout tasks, removing any that are no longer
> +		 * holdouts.  When the list is empty, we are done.
> +		 */
> +		while (!list_empty(&rcu_tasks_holdouts)) {
> +			schedule_timeout_interruptible(HZ / 10);
> +			flush_signals(current);
> +			rcu_read_lock();
> +			list_for_each_entry_rcu(t, &rcu_tasks_holdouts,
> +						rcu_tasks_holdout_list) {
> +				if (smp_load_acquire(&t->rcu_tasks_holdout))
> +					continue;
> +				list_del_init(&t->rcu_tasks_holdout_list);
> +				/* @@@ need to check for usermode on CPU. */
> +			}
> +			rcu_read_unlock();

Maybe I missed something. The task @t may already exited and we access to
the stale memory here if without patch 8/9.
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