Re: Fw: [PATCH -mm] workqueue: debug possible endless loop in cancel_rearming_delayed_work

From: Oleg Nesterov
Date: Wed Apr 25 2007 - 11:43:05 EST

On 04/25, Oleg Nesterov wrote:
> On 04/25, Jarek Poplawski wrote:
> >
> > Probably this is also possible without timer i.e.
> > with queue_work.
> Yes, thanks. While adding cpu-hotplug check I forgot to add ->current_work
> check, which is needed to actually implement this
> > > Note that cancel_rearming_delayed_work() now can handle the works
> > > which re-arm itself via queue_work(), not only queue_delayed_work().
> part. I'll resend after fix.

Hm. But can't we do better? Looks like we don't need to check ->current_work,

void cancel_rearming_delayed_work(struct delayed_work *dwork)
struct work_struct *work = &dwork->work;
struct cpu_workqueue_struct *cwq = get_wq_data(work);
int done;

do {
done = 1;

if (!list_empty(&work->entry))
else if (test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work)))
done = del_timer(&dwork->timer)

} while (!done);

* Nobody can clear WORK_STRUCT_PENDING. This means that the
* work can't be re-queued and the timer can't be re-started.
needs_a_good_name(cwq->wq, work);

Jarek, I didn't think much about this, just a new idea. I am posting this code
in a hope you can review it while I sleep on this... CPU-hotplug is ignored for
now. Note that this version doesn't need the change in run_workqueue().


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