linux-kernel - Re: [PATCH 2/3] rcu: Defer RCU kthreads wakeup when CPU is dying

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Date: Tue, 19 Dec 2023 16:47:20 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Boqun Feng <boqun.feng@...il.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Neeraj Upadhyay <neeraj.upadhyay@....com>,
	Uladzislau Rezki <urezki@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>, rcu <rcu@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/3] rcu: Defer RCU kthreads wakeup when CPU is dying

On Tue, Dec 19, 2023 at 07:29:23AM -0800, Paul E. McKenney wrote:
> > +static void swake_up_one_online(struct swait_queue_head *wqh)
> > +{
> > +	int cpu = get_cpu();
> 
> This works because get_cpu() is currently preempt_disable().  If there are plans to
> make get_cpu() be some sort of read lock, we might deadlock when synchronize_rcu()
> is invoked from a CPU-hotplug notifier, correct?
> 
> Might this be worth a comment somewhere at some point?

Sure, I can add that.

Thanks.