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

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Date:   Wed, 28 Jun 2017 16:15:09 -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 tomorrow.  My only concern about that is the use of WARN_ON().
As I may have mentioned in my note of 6/27, I saw about 600 instances of the warning
message just during boot of the PowerPC kernel.  I doubt that we want to see that on
an ongoing basis.

Michael

On 06/13/2017 03:10 PM, Tejun Heo wrote:
> Hello,
> 
> On Tue, Jun 13, 2017 at 03:04:30PM -0500, Michael Bringmann wrote:
>> @@ -3564,19 +3564,28 @@ static struct pool_workqueue *alloc_unbound_pwq(struct workqueue_struct *wq,
>>  static bool wq_calc_node_cpumask(const struct workqueue_attrs *attrs, int node,
>>  				 int cpu_going_down, cpumask_t *cpumask)
>>  {
>> +	cpumask_t	onl_targ_cm;
>> +
>>  	if (!wq_numa_enabled || attrs->no_numa)
>>  		goto use_dfl;
>>  
>>  	/* does @node have any online CPUs @attrs wants? */
>> -	cpumask_and(cpumask, cpumask_of_node(node), attrs->cpumask);
>> +	cpumask_and(&onl_targ_cm, cpumask_of_node(node), attrs->cpumask);
>>  	if (cpu_going_down >= 0)
>> -		cpumask_clear_cpu(cpu_going_down, cpumask);
>> +		cpumask_clear_cpu(cpu_going_down, &onl_targ_cm);
>>  
>> -	if (cpumask_empty(cpumask))
>> +	if (cpumask_empty(&onl_targ_cm))
>>  		goto use_dfl;
>>  
>>  	/* yeap, return possible CPUs in @node that @attrs wants */
>>  	cpumask_and(cpumask, attrs->cpumask, wq_numa_possible_cpumask[node]);
>> +
>> +	if (cpumask_weight(&onl_targ_cm) > cpumask_weight(cpumask)) {
>> +		printk(KERN_INFO "WARNING: WQ cpumask: onl intersect > "
>> +						"possible intersect\n");
>> +		return false;
>> +	}
> 
> Yeah, alternatively, we can just add right before returning,
> 
> 	if (WARN_ON(cpumask_empty(cpumask)))
> 		return false;
> 
> Thanks.
> 

-- 
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