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

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Message-ID: <20100428194028.GA16389@redhat.com>
Date:	Wed, 28 Apr 2010 21:40:28 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Arve Hjønnevåg <arve@...roid.com>
Cc:	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	Tejun Heo <tj@...nel.org>, Pavel Machek <pavel@....cz>,
	Len Brown <len.brown@...el.com>
Subject: Re: [PATCH 6/8] PM: Add suspend blocking work.

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.

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