linux-kernel - Re: [PATCH v6] workqueue: Fix edge cases for calc of pool's cpumask

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Message-Id: <47ac4fb9-a316-0125-7d4e-73cf602d891e@linux.vnet.ibm.com>
Date:   Thu, 27 Jul 2017 13:42:16 -0500
From:   Nathan Fontenot <nfont@...ux.vnet.ibm.com>
To:     Michael Bringmann <mwb@...ux.vnet.ibm.com>,
        Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6] workqueue: Fix edge cases for calc of pool's cpumask

On 07/27/2017 01:15 PM, Michael Bringmann wrote:
> 
> On NUMA systems with dynamic processors, the content of the cpumask
> may change over time.  As new processors are added via DLPAR operations,
> workqueues are created for them.  Depending upon the order in which CPUs
> are added/removed, we may run into problems with the content of the
> cpumask used by the workqueues.  This patch deals with situations where
> the online cpumask for a node is a proper superset of possible cpumask
> for the node.  It also deals with edge cases where the order in which
> CPUs are removed/added from the online cpumask may leave the set for a
> node empty, and require execution by CPUs on another node.
> 
> In these and other cases, the patch attempts to ensure that a valid,
> usable cpumask is used to set up newly created pools for workqueues.
> This patch provides a fix for NUMA systems which can add/subtract
> processors dynamically.  The patch is expected to be an intermediate
> one while developers search for any underlying issues.
> 
> [With additions to the patch provided by Tejun Hao <tj@...nel.org>]
> 
> Signed-off-by: Michael Bringmann <mwb@...ux.vnet.ibm.com>
> ---
> Changes in V6:
>   -- Update descriptive text
> ---
>  kernel/workqueue.c |    7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index c74bf39..6b6d540 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -3577,6 +3577,13 @@ static bool wq_calc_node_cpumask(const struct workqueue_attrs *attrs, int node,
> 
>  	/* yeap, return possible CPUs in @node that @attrs wants */
>  	cpumask_and(cpumask, attrs->cpumask, wq_numa_possible_cpumask[node]);
> +
> +	if (cpumask_empty(cpumask)) {
> +		pr_warn_once("WARNING: workqueue cpumask: onl intersect > "
                                                          ^^^
This message doesn't seem right, or I am missing something, "onl"?

-Nathan

> +				"possible intersect\n");
> +		return false;
> +	}
> +
>  	return !cpumask_equal(cpumask, attrs->cpumask);
> 
>  use_dfl:
>