Re: [PATCH 2/2] workqueue: Fix affinity of kworkers attached during late hotplug

Valentin Schneider
2020-12-11T13:15:36Z

On 11/12/20 12:51, Valentin Schneider wrote:
>> In that case maybe we should check for the cpu_active_mask here too ?
>
> Looking at it again, I think we might need to.
>
> IIUC you can end up with pools bound to a single NUMA node (?). In that
> case, say the last CPU of a node is going down, then:
>
> workqueue_offline_cpu()
> wq_update_unbound_numa()
> alloc_unbound_pwq()
> get_unbound_pool()
>
> would still pick that node, because it doesn't look at the online / active
> mask. And at this point, we would affine the
> kworkers to that node, and we're back to having kworkers enqueued on a
> (!active, online) CPU that is going down...

Assuming a node covers at least 2 CPUs, that can't actually happen per
is_cpu_allowed().