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

Vincent Donnefort
2020-12-11T13:18:32Z

On Fri, Dec 11, 2020 at 01:13:35PM +0000, Valentin Schneider wrote:
> 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().

Yes indeed, my bad, no problem here.