linux-kernel - Re: [PATCH] rcu: Avoid boost task running on isolated cpus

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Message-ID: <20211115131145.GE641268@paulmck-ThinkPad-P17-Gen-1>
Date:   Mon, 15 Nov 2021 05:11:45 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Zqiang <qiang.zhang1211@...il.com>
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        frederic@...nel.org
Subject: Re: [PATCH] rcu: Avoid boost task running on isolated cpus

On Mon, Nov 15, 2021 at 01:15:46PM +0800, Zqiang wrote:
> If the nohz_full is enabled, when the boost task be created,
> the cpus_allowed_ptr be set housekeeping_cpumask(HK_FLAG_KTHREAD),
> however when the rcu_boost_kthread_setaffinity() be called, the
> original affinity will be changed, the isolated cpus should be
> considered again.
> 
> Signed-off-by: Zqiang <qiang.zhang1211@...il.com>

I have queued this for testing and further review, thank you!

I am particularly interested in Frederic's thoughts on how this might
interact with any future ability to change the set of nohz_full CPUs
at runtime.

							Thanx, Paul

> ---
>  kernel/rcu/tree_plugin.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 5199559fbbf0..87e7ebbdb12e 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -1204,8 +1204,9 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
>  		if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
>  		    cpu != outgoingcpu)
>  			cpumask_set_cpu(cpu, cm);
> +	cpumask_and(cm, cm, housekeeping_cpumask(HK_FLAG_RCU));
>  	if (cpumask_weight(cm) == 0)
> -		cpumask_setall(cm);
> +		cpumask_copy(cm, housekeeping_cpumask(HK_FLAG_RCU));
>  	set_cpus_allowed_ptr(t, cm);
>  	free_cpumask_var(cm);
>  }
> -- 
> 2.17.1
>