linux-kernel - Re: [PATCH v2] rcu: Change return type of rcu_spawn_one_boost

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Date:   Thu, 27 Jun 2019 09:42:40 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Byungchul Park <byungchul.park@....com>
Cc:     paulmck@...ux.ibm.com, josh@...htriplett.org, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@....com
Subject: Re: [PATCH v2] rcu: Change return type of
 rcu_spawn_one_boost_kthread()

On Thu, Jun 27, 2019 at 04:07:46PM +0900, Byungchul Park wrote:
> Hello,
> 
> I tested if the WARN_ON_ONCE() is fired with my box and it was ok.

Looks pretty safe to me and nice clean up!

Acked-by: Joel Fernandes (Google) <joel@...lfernandes.org>

 - Joel

> 
> Thanks,
> Byungchul
> 
> Changes from v1
> -. WARN_ON_ONCE() on failing to create rcu_boost_kthread.
> -. Changed title and commit message a bit.
> 
> ---8<---
> From 7100fcf82202f063f70f45def208ea5198412f5a Mon Sep 17 00:00:00 2001
> From: Byungchul Park <byungchul.park@....com>
> Date: Thu, 27 Jun 2019 15:58:10 +0900
> Subject: [PATCH v2] rcu: Change return type of rcu_spawn_one_boost_kthread()
> 
> The return value of rcu_spawn_one_boost_kthread() is not used any
> longer. Change return type of that function from int to void.
> 
> Signed-off-by: Byungchul Park <byungchul.park@....com>
> ---
>  kernel/rcu/tree_plugin.h | 17 ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 1102765..3c8444e 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -1131,7 +1131,7 @@ static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
>   * already exist.  We only create this kthread for preemptible RCU.
>   * Returns zero if all is well, a negated errno otherwise.
>   */
> -static int rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
> +static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
>  {
>  	int rnp_index = rnp - rcu_get_root();
>  	unsigned long flags;
> @@ -1139,25 +1139,24 @@ static int rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
>  	struct task_struct *t;
>  
>  	if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
> -		return 0;
> +		return;
>  
>  	if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
> -		return 0;
> +		return;
>  
>  	rcu_state.boost = 1;
>  	if (rnp->boost_kthread_task != NULL)
> -		return 0;
> +		return;
>  	t = kthread_create(rcu_boost_kthread, (void *)rnp,
>  			   "rcub/%d", rnp_index);
> -	if (IS_ERR(t))
> -		return PTR_ERR(t);
> +	if (WARN_ON_ONCE(IS_ERR(t)))
> +		return;
>  	raw_spin_lock_irqsave_rcu_node(rnp, flags);
>  	rnp->boost_kthread_task = t;
>  	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
>  	sp.sched_priority = kthread_prio;
>  	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
>  	wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
> -	return 0;
>  }
>  
>  static void rcu_cpu_kthread_setup(unsigned int cpu)
> @@ -1265,7 +1264,7 @@ static void __init rcu_spawn_boost_kthreads(void)
>  	if (WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec), "%s: Could not start rcub kthread, OOM is now expected behavior\n", __func__))
>  		return;
>  	rcu_for_each_leaf_node(rnp)
> -		(void)rcu_spawn_one_boost_kthread(rnp);
> +		rcu_spawn_one_boost_kthread(rnp);
>  }
>  
>  static void rcu_prepare_kthreads(int cpu)
> @@ -1275,7 +1274,7 @@ static void rcu_prepare_kthreads(int cpu)
>  
>  	/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
>  	if (rcu_scheduler_fully_active)
> -		(void)rcu_spawn_one_boost_kthread(rnp);
> +		rcu_spawn_one_boost_kthread(rnp);
>  }
>  
>  #else /* #ifdef CONFIG_RCU_BOOST */
> -- 
> 1.9.1
>