linux-kernel - Re: [PATCH wq/for-4.5-fixes] workqueue: handle NUMA_NO_NODE for unbound pool

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Message-ID: <20160215173346.GA26207@dhcp22.suse.cz>
Date:	Mon, 15 Feb 2016 18:33:46 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Mike Galbraith <umgwanakikbuti@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH wq/for-4.5-fixes] workqueue: handle NUMA_NO_NODE for
 unbound pool_workqueue lookup

On Wed 10-02-16 10:55:03, Tejun Heo wrote:
[...]
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -570,6 +570,16 @@ static struct pool_workqueue *unbound_pwq_by_node(struct workqueue_struct *wq,
>  						  int node)
>  {
>  	assert_rcu_or_wq_mutex_or_pool_mutex(wq);
> +
> +	/*
> +	 * XXX: @node can be NUMA_NO_NODE if CPU goes offline while a
> +	 * delayed item is pending.  The plan is to keep CPU -> NODE
> +	 * mapping valid and stable across CPU on/offlines.  Once that
> +	 * happens, this workaround can be removed.

I am not sure this is completely true with the code as is currently.
Don't wee also need to use cpu_to_mem to handle memoryless CPUs?

> +	 */
> +	if (unlikely(node == NUMA_NO_NODE))
> +		return wq->dfl_pwq;
> +
>  	return rcu_dereference_raw(wq->numa_pwq_tbl[node]);
>  }


diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index c579dbab2e36..4785b895b9b5 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1325,7 +1325,7 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
 	if (!(wq->flags & WQ_UNBOUND))
 		pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);
 	else
-		pwq = unbound_pwq_by_node(wq, cpu_to_node(cpu));
+		pwq = unbound_pwq_by_node(wq, cpu_to_mem(cpu));
 
 	/*
 	 * If @work was previously on a different pool, it might still be

-- 
Michal Hocko
SUSE Labs