linux-kernel - Re: [PATCH v2 4/6] rcu-tasks: Maintain lists to eliminate RCU-tasks/do

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Date: Fri, 23 Feb 2024 13:19:42 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Boqun Feng <boqun.feng@...il.com>
Cc: linux-kernel@...r.kernel.org, rcu@...r.kernel.org,
	Neeraj Upadhyay <Neeraj.Upadhyay@....com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Chen Zhongjin <chenzhongjin@...wei.com>,
	Yang Jihong <yangjihong1@...wei.com>,
	Neeraj Upadhyay <quic_neeraju@...cinc.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>
Subject: Re: [PATCH v2 4/6] rcu-tasks: Maintain lists to eliminate
 RCU-tasks/do_exit() deadlocks

On Fri, Feb 16, 2024 at 05:27:39PM -0800, Boqun Feng wrote:
> -void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu)
> +void exit_tasks_rcu_start(void)
>  {
> -	current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu);
> +	unsigned long flags;
> +	struct rcu_tasks_percpu *rtpcp;
> +	struct task_struct *t = current;
> +
> +	WARN_ON_ONCE(!list_empty(&t->rcu_tasks_exit_list));
> +	preempt_disable();
> +	rtpcp = this_cpu_ptr(rcu_tasks.rtpcpu);
> +	t->rcu_tasks_exit_cpu = smp_processor_id();
> +	raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
> +	if (!rtpcp->rtp_exit_list.next)

And then you might want to turn that into a WARN_ONCE.

Thanks.

> +		INIT_LIST_HEAD(&rtpcp->rtp_exit_list);
> +	list_add(&t->rcu_tasks_exit_list, &rtpcp->rtp_exit_list);
> +	raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
> +	preempt_enable();
>  }