Re: [PATCH v2 4/6] rcu-tasks: Maintain lists to eliminate RCU-tasks/do_exit() deadlocks

[Frederic Weisbecker <frederic@kernel.org>]

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();
>  }