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[PATCH] workqueue: Ensure that cpumask set for pools created after boot

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  [PATCH] workqueue: Ensure that cpumask set for pools created after  boot Michael Bringmann <mwb@linux.vnet.ibm.com> - 2017-05-10 18:50 +0200
    Re: [PATCH] workqueue: Ensure that cpumask set for pools created  after boot Tejun Heo <tj@kernel.org> - 2017-05-10 19:40 +0200

#1638963 — [PATCH] workqueue: Ensure that cpumask set for pools created after boot

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.  This patch ensures that the pools
created for new workqueues will be initialized with a cpumask before
the first worker is created, attached, and woken up.  If the mask is
not set up, then the kernel will crash when 'wakeup_process' is unable
to find a valid CPU to which to assign the new worker.

Signed-off-by: Michael Bringmann <mwb@linux.vnet.ibm.com>
---
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index c74bf39..6091069 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3366,6 +3366,8 @@ static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
 	copy_workqueue_attrs(pool->attrs, attrs);
 	pool->node = target_node;
 
+	cpumask_copy(pool->attrs->cpumask, cpumask_of(smp_processor_id()));
+
 	/*
 	 * no_numa isn't a worker_pool attribute, always clear it.  See
 	 * 'struct workqueue_attrs' comments for detail.

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#1638981 — Re: [PATCH] workqueue: Ensure that cpumask set for pools created after boot

Hello,

On Wed, May 10, 2017 at 11:48:17AM -0500, 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.  This patch ensures that the pools
> created for new workqueues will be initialized with a cpumask before
> the first worker is created, attached, and woken up.  If the mask is
> not set up, then the kernel will crash when 'wakeup_process' is unable
> to find a valid CPU to which to assign the new worker.
> 
> Signed-off-by: Michael Bringmann <mwb@linux.vnet.ibm.com>
> ---
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index c74bf39..6091069 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -3366,6 +3366,8 @@ static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
>  	copy_workqueue_attrs(pool->attrs, attrs);
>  	pool->node = target_node;
>  
> +	cpumask_copy(pool->attrs->cpumask, cpumask_of(smp_processor_id()));

What prevents a cpu getting added right here tho?

Maybe the right thing to do is protecting the whole thing with hotplug
readlock?

Thanks.

-- 
tejun

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