linux-kernel - Re: [PATCH v3] rcu: Change return type of rcu_spawn_one_boost

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Date:   Tue, 2 Jul 2019 14:11:03 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc:     josh@...htriplett.org, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        joel@...lfernandes.org, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@....com
Subject: Re: [PATCH v3] rcu: Change return type of
 rcu_spawn_one_boost_kthread()

On Mon, Jul 01, 2019 at 01:12:16PM -0700, Paul E. McKenney wrote:
> On Mon, Jul 01, 2019 at 09:40:39AM +0900, Byungchul Park wrote:
> > Hello,
> > 
> > I tested again if the WARN_ON_ONCE() is fired with my box.
> > 
> > And it was OK.
> > 
> > Thanks,
> > Byungchul
> 
> And it now applies just fine, so I have queued it, thank you!
> 
> In the future, could you please use something like "git send-email"
> to email a proper patch?  When you do it this way, after I do "git am",
> I have to hand-edit the commit to remove this preamble.

Oh! Sorry to hear that. I've been always using "git send-email" with
scissors in the body expecting you do "git am -c". Do you mean it's not
a good way, right? I won't use the scissors again.

> But while I was doing the hand-editing, I updated the commit log as
> follows:
> 
> 	rcu: Change return type of rcu_spawn_one_boost_kthread()
> 
> 	The return value of rcu_spawn_one_boost_kthread() is not used
> 	any longer.  This commit therefore changes its return type from
> 	int to void, and removes the cast to void from its callers.
> 
> Does that work for you?

Sure. Thank you.

Thanks,
Byungchul

> 						Thanx, Paul
> 
> > Changes from v2
> > -. Port the patch to a1af11a24cb0 (Paul's request)
> > -. Add a few new lines for a better look
> > 
> > Changes from v1
> > -. WARN_ON_ONCE() on failing to create rcu_boost_kthread.
> > -. Changed title and commit message a bit.
> > 
> > ---8<---
> > >From 20c934c5657a7a0f13ebb050ffd350d4174965d0 Mon Sep 17 00:00:00 2001
> > From: Byungchul Park <byungchul.park@....com>
> > Date: Mon, 1 Jul 2019 09:27:15 +0900
> > Subject: [PATCH v3] 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 | 20 +++++++++++---------
> >  1 file changed, 11 insertions(+), 9 deletions(-)
> > 
> > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> > index c588ef9..b8eea22 100644
> > --- a/kernel/rcu/tree_plugin.h
> > +++ b/kernel/rcu/tree_plugin.h
> > @@ -1119,7 +1119,7 @@ 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;
> > @@ -1127,25 +1127,27 @@ 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;
> >  }
> >  
> >  /*
> > @@ -1186,7 +1188,7 @@ static void __init rcu_spawn_boost_kthreads(void)
> >  	struct rcu_node *rnp;
> >  
> >  	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)
> > @@ -1196,7 +1198,7 @@ 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
> >