linux-kernel - Re: [PATCH 2/5] rcu/tree: Fix SCHED

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Message-ID: <20190801135103.GI5913@linux.ibm.com>
Date:   Thu, 1 Aug 2019 06:51:03 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org,
        Juri Lelli <juri.lelli@...hat.com>
Subject: Re: [PATCH 2/5] rcu/tree: Fix SCHED_FIFO params

On Thu, Aug 01, 2019 at 01:13:50PM +0200, Peter Zijlstra wrote:
> A rather embarrasing mistake had us call sched_setscheduler() before
> initializing the parameters passed to it.
> 
> Cc: Juri Lelli <juri.lelli@...hat.com>
> Cc: "Paul E. McKenney" <paulmck@...ux.ibm.com>

Thank you for having CCed me this time.  ;-)

Reviewed-by: Paul E. McKenney <paulmck@...ux.ibm.com>

> Fixes: 1a763fd7c633 ("rcu/tree: Call setschedule() gp ktread to SCHED_FIFO outside of atomic region")
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  kernel/rcu/tree.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -3234,13 +3234,13 @@ static int __init rcu_spawn_gp_kthread(v
>  	t = kthread_create(rcu_gp_kthread, NULL, "%s", rcu_state.name);
>  	if (WARN_ONCE(IS_ERR(t), "%s: Could not start grace-period kthread, OOM is now expected behavior\n", __func__))
>  		return 0;
> -	if (kthread_prio)
> +	if (kthread_prio) {
> +		sp.sched_priority = kthread_prio;
>  		sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
> +	}
>  	rnp = rcu_get_root();
>  	raw_spin_lock_irqsave_rcu_node(rnp, flags);
>  	rcu_state.gp_kthread = t;
> -	if (kthread_prio)
> -		sp.sched_priority = kthread_prio;
>  	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
>  	wake_up_process(t);
>  	rcu_spawn_nocb_kthreads();
> 
>