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    SubjectRe: Fw: [PATCH -mm] workqueue: debug possible endless loop in cancel_rearming_delayed_work
    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;
    spin_lock_irq(&cwq->lock);

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

    spin_unlock_irq(&cwq->lock);
    } 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);
    work_clear_pending(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().

    Oleg.

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