linux-kernel - Re: [PATCH] cgroup/cpuset: fix circular locking dependency

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Message-ID: <20180109134448.GE3668920@devbig577.frc2.facebook.com>
Date:   Tue, 9 Jan 2018 05:44:48 -0800
From:   Tejun Heo <tj@...nel.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Prateek Sood <prsood@...eaurora.org>,
        Peter Zijlstra <peterz@...radead.org>, avagin@...il.com,
        mingo@...nel.org, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, sramana@...eaurora.org
Subject: Re: [PATCH] cgroup/cpuset: fix circular locking dependency

Hello, Paul.

On Mon, Jan 08, 2018 at 08:20:16PM -0800, Paul E. McKenney wrote:
> OK, so I can put WQ_MEM_RECLAIM on the early boot creation of RCU's
> workqueue_struct as shown below, right?

Yes, this looks good to me.  Just one question.

> +struct workqueue_struct *rcu_gp_workqueue;
> +
>  void __init rcu_init(void)
>  {
>  	int cpu;
> @@ -4298,6 +4300,10 @@ void __init rcu_init(void)
>  		rcu_cpu_starting(cpu);
>  		rcutree_online_cpu(cpu);
>  	}
> +
> +	/* Create workqueue for expedited GPs and for Tree SRCU. */
> +	rcu_gp_workqueue = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
> +	WARN_ON(!rcu_gp_workqueue);

The code was previously using both system_power_efficient_wq and
system_workqueue (for the expedited path).  I guess the options were
either using two workqueues or dropping POWER_EFFICIENT.  I have no
idea how big an impact this will make or whether it'd even be
noticeable but maybe it'd be worthwhile to mention that in the
description?

Thanks.

-- 
tejun