On Tue, Sep 18, 2012 at 04:36:53PM +0800, Lai Jiangshan wrote:
> The whole workqueue.c keeps activate-order equals to queue_work()-order
> in any given cwq except workqueue_set_max_active().
>
> If this order is not kept, something may be not good:
>
> first_work_fn() { release some resource; }
> second_work_fn() { wait and request the resource; use resource; }
>
> 1. user queues the first work. # ->max_active is low, is queued on
> ->delayed_works.
> 2. someone increases the >max_active via workqueue_set_max_active()
> 3. user queues the second work. # queued on cwq->pool.
>
> When the second work is launched to execute, it waits the first work
> to release the resource. But the first work is still in ->delayed_works,
> it waits the first work to finish and them it can be activated.
>
> It is bad. we fix it by activating the first work in the step 2.
>
> I can't fully determine that it is workqueue's responsibility
> or the user's responsibility.
> If it is workqueue's responsibility, the patch needs go to -stable.
> If it is user's responsibility. it is a nice cleanup, it can go to for-next.
> I prefer it is workqueue's responsibility.
Unless max_active == 1, workqueue doesn't give any guarantee on
execution order. I don't think we need to care about this.
Thanks.
--
tejun
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