[PATCH V2] workqueue: Ensure that cpumask set for pools created after boot

[PATCH V2] workqueue: Ensure that cpumask set for pools created after boot

[Michael Bringmann]

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>
---
Changes in V2:
  -- Only fill in empty cpumasks.
---
 kernel/workqueue.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index c74bf39..1b16ac4 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3366,6 +3366,9 @@ static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
 	copy_workqueue_attrs(pool->attrs, attrs);
 	pool->node = target_node;
 
+	if (!cpumask_weight(pool->attrs->cpumask))
+		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.

Re: [PATCH V2] workqueue: Ensure that cpumask set for pools created after boot

[Tejun Heo]

Hello, Michael.

On Thu, May 25, 2017 at 09:55:10AM -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>
> ---
> Changes in V2:
>   -- Only fill in empty cpumasks.
> ---
>  kernel/workqueue.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index c74bf39..1b16ac4 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -3366,6 +3366,9 @@ static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
>  	copy_workqueue_attrs(pool->attrs, attrs);
>  	pool->node = target_node;
>  
> +	if (!cpumask_weight(pool->attrs->cpumask))
> +		cpumask_copy(pool->attrs->cpumask, cpumask_of(smp_processor_id()));
> +

So, the problem is that control is reaching here with empty mask.
Filling it with an arbitrary cpu id doesn't really fix the bug.  I
think I just messed up wq_calc_node_cpumask().  Will send a fix soon.

Thanks.

-- 
tejun