Re: [PATCH] workqueue: Add pool_workqueue to pending_pwqs list when unplugging multiple inactive works

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Mar 31, 2026 at 02:05:41PM -1000, Tejun Heo wrote:
> Hello,
> 
> On Tue, Mar 31, 2026 at 03:18:39PM -0700, Matthew Brost wrote:
> > @@ -1849,8 +1849,20 @@ static void unplug_oldest_pwq(struct workqueue_struct *wq)
> >  	raw_spin_lock_irq(&pwq->pool->lock);
> >  	if (pwq->plugged) {
> >  		pwq->plugged = false;
> > -		if (pwq_activate_first_inactive(pwq, true))
> > +		if (pwq_activate_first_inactive(pwq, true)) {
> > +			if (!list_empty(&pwq->inactive_works)) {
> > +				struct worker_pool *pool = pwq->pool;
> > +				struct wq_node_nr_active *nna =
> > +					wq_node_nr_active(wq, pool->node);
> > +
> > +				raw_spin_lock(&nna->lock);
> > +				if (list_empty(&pwq->pending_node))
> > +					list_add_tail(&pwq->pending_node,
> > +						      &nna->pending_pwqs);
> > +				raw_spin_unlock(&nna->lock);
> > +			}
> 
> It's a bit gnarly to open code locking and list operation. Would just
> calling pwq_activate_first_inactive(pwq, false) one more time work here?
> That'd trigger tryinc_node_nr_active() failure in pwq_tryinc_nr_active() and
> the addition to the pending list. As this is quite subtle, it'd be nice to
> have some comment - it's compensating for the missed pwq_tryinc_nr_active()
> call due to plugging, right?

Yeah, I think that will work. Let me verify with my reproducer and
adjust the patch accordingly.

+1 on the comment as well—very subtle. Took a few days of
reverse-engineering work queues to track down.

Matt

> 
> Thanks.
> 
> -- 
> tejun