Hi Hillf, thanks for the review
On Sat, Apr 03, 2021 at 10:09:02AM +0800, Hillf Danton wrote:
> On Fri, 2 Apr 2021 12:16:32 Dan Schatzberg wrote:
> > +queue_work:
> > + if (worker) {
> > + /*
> > + * We need to remove from the idle list here while
> > + * holding the lock so that the idle timer doesn't
> > + * free the worker
> > + */
> > + if (!list_empty(&worker->idle_list))
> > + list_del_init(&worker->idle_list);
>
> Nit, only queue work if the worker is inactive - otherwise it is taking
> care of the cmd_list.
By worker is inactive, you mean worker is on the idle_list? Yes, I
think you're right that queue_work() is unnecessary in that case since
each worker checks empty cmd_list then adds itself to idle_list under
the lock.
>
> > + work = &worker->work;
> > + cmd_list = &worker->cmd_list;
> > + } else {
> > + work = &lo->rootcg_work;
> > + cmd_list = &lo->rootcg_cmd_list;
> > + }
> > + list_add_tail(&cmd->list_entry, cmd_list);
> > + queue_work(lo->workqueue, work);
> > + spin_unlock_irq(&lo->lo_work_lock);
> > }
> [...]
> > + /*
> > + * We only add to the idle list if there are no pending cmds
> > + * *and* the worker will not run again which ensures that it
> > + * is safe to free any worker on the idle list
> > + */
> > + if (worker && !work_pending(&worker->work)) {
>
> The empty cmd_list is a good enough reason for worker to become idle.
This is only true with the above change to avoid a gratuitous
queue_work(), right? Otherwise we run the risk of freeing a worker
concurrently with loop_process_work() being invoked.
