linux-kernel - Re: [PATCH] workqueue: Ensure that cpumask set for pools created after boot

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Message-Id: <f0723547-1383-efa2-a691-eb91ff0620c4@linux.vnet.ibm.com>
Date:   Thu, 25 May 2017 10:30:46 -0500
From:   Michael Bringmann <mwb@...ux.vnet.ibm.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org,
        Nathan Fontenot <nfont@...ux.vnet.ibm.com>
Subject: Re: [PATCH] workqueue: Ensure that cpumask set for pools created
 after boot

I will try that patch shortly.  I also updated my patch to be conditional
on whether the pool's cpumask attribute was empty.  You should have received
V2 of that patch by now.

As to your remark about 'proper subset of possible cpumask for the node',
would that not be the case when we are removing VPs?

On 05/25/2017 10:07 AM, Tejun Heo wrote:
> On Thu, May 25, 2017 at 11:03:53AM -0400, Tejun Heo wrote:
>> wq_update_unbound_numa() should have never called into
>> alloc_unbound_pwq() w/ empty node cpu mask.  It should have fallen
>> back to the dfl_pwq.  It looks like I just messed up the logic there
>> from the initial commit of the feature.  Can you please see whether
>> the following fixes the problem?
> 
> Can you please try the following instead.  On the second thought, I
> don't think the current logic is wrong.  If this fixes the issue,
> somehow your setup is having a situation where online cpumask for a
> node is a proper superset of possible cpumask for the node.
> 
> Thanks.
> 
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index c74bf39ef764..4da5ff649ff8 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -3559,13 +3559,13 @@ static struct pool_workqueue *alloc_unbound_pwq(struct workqueue_struct *wq,
>   * stable.
>   *
>   * Return: %true if the resulting @cpumask is different from @attrs->cpumask,
> - * %false if equal.
> + * %false if equal.  On %false return, the content of @cpumask is undefined.
>   */
>  static bool wq_calc_node_cpumask(const struct workqueue_attrs *attrs, int node,
>  				 int cpu_going_down, cpumask_t *cpumask)
>  {
>  	if (!wq_numa_enabled || attrs->no_numa)
> -		goto use_dfl;
> +		return false;
> 
>  	/* does @node have any online CPUs @attrs wants? */
>  	cpumask_and(cpumask, cpumask_of_node(node), attrs->cpumask);
> @@ -3573,15 +3573,13 @@ static bool wq_calc_node_cpumask(const struct workqueue_attrs *attrs, int node,
>  		cpumask_clear_cpu(cpu_going_down, cpumask);
> 
>  	if (cpumask_empty(cpumask))
> -		goto use_dfl;
> +		return false;
> 
>  	/* yeap, return possible CPUs in @node that @attrs wants */
>  	cpumask_and(cpumask, attrs->cpumask, wq_numa_possible_cpumask[node]);
> -	return !cpumask_equal(cpumask, attrs->cpumask);
> 
> -use_dfl:
> -	cpumask_copy(cpumask, attrs->cpumask);
> -	return false;
> +	return !cpumask_empty(cpumask) &&
> +		!cpumask_equal(cpumask, attrs->cpumask);
>  }
> 
>  /* install @pwq into @wq's numa_pwq_tbl[] for @node and return the old pwq */
> 
> 

-- 
Michael W. Bringmann
Linux Technology Center
IBM Corporation
Tie-Line  363-5196
External: (512) 286-5196
Cell:       (512) 466-0650
mwb@...ux.vnet.ibm.com