linux-kernel - Re: [PATCH rcu 3/3] rcu: Allow expedited RCU grace periods on incoming CPUs

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Message-ID: <YgK81N+w/zsW12N9@slm.duckdns.org>
Date:   Tue, 8 Feb 2022 08:56:20 -1000
From:   Tejun Heo <tj@...nel.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, rostedt@...dmis.org,
        Mukesh Ojha <quic_mojha@...cinc.com>
Subject: Re: [PATCH rcu 3/3] rcu: Allow expedited RCU grace periods on
 incoming CPUs

On Fri, Feb 04, 2022 at 02:55:07PM -0800, Paul E. McKenney wrote:
> Although it is usually safe to invoke synchronize_rcu_expedited() from a
> preemption-enabled CPU-hotplug notifier, if it is invoked from a notifier
> between CPUHP_AP_RCUTREE_ONLINE and CPUHP_AP_ACTIVE, its attempts to
> invoke a workqueue handler will hang due to RCU waiting on a CPU that
> the scheduler is not paying attention to.  This commit therefore expands
> use of the existing workqueue-independent synchronize_rcu_expedited()
> from early boot to also include CPUs that are being hotplugged.
> 
> Link: https://lore.kernel.org/lkml/7359f994-8aaf-3cea-f5cf-c0d3929689d6@quicinc.com/
> Reported-by: Mukesh Ojha <quic_mojha@...cinc.com>
> Cc: Tejun Heo <tj@...nel.org>
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun