Re: [PATCH 6/8] PM: Add suspend blocking work.

Oleg Nesterov
2010-04-28T19:40:28Z

On 04/27, Arve Hjønnevåg wrote:
>
> Allow work to be queued that will block suspend while it is pending
> or executing. To get the same functionality in the calling code often
> requires a separate suspend_blocker for pending and executing work, or
> additional state and locking. This implementation does add additional
> state and locking, but this can be removed later if we add support for
> suspend blocking work to the core workqueue code.

I think this patch is fine.

Just one silly question,

> +int queue_suspend_blocking_work(struct workqueue_struct *wq,
> + struct suspend_blocking_work *work)
> +{
> + int ret;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&work->lock, flags);
> + suspend_block(&work->suspend_blocker);
> + ret = queue_work(wq, &work->work);
> + if (ret)
> + work->active++;

why not

ret = queue_work(wq, &work->work);
if (ret) {
suspend_block(&work->suspend_blocker);
work->active++;
}

?

Afaics, we can't race with work->func() doing unblock, we hold work-lock.
And this way the code looks more clear.

Sorry, I had no chance to read the previous patches. After the quick look
at 1/8 I think it is OK to call suspend_block() twice, but still...

Or I missed something? Just curious.

Hmm... actually, queue_work() can also fail if we race with cancel_ which
temporary sets WORK_STRUCT_PENDING. In that case suspend_block() won't
be paired by unblock ?

> +int schedule_suspend_blocking_work(struct suspend_blocking_work *work)
> +{
> ...
> + ret = schedule_work(&work->work);

Off-topic. We should probably export keventd_wq to avoid the duplications
like this.

Oleg.