From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Rafael J. Wysocki" <rjw@sisk.pl>
Subject: Re: [PATCH 6/8] PM: Add suspend blocking work.
Date: Wed, 28 Apr 2010 23:09:42 +0200
Message-ID: <201004282309.42188.rjw@sisk.pl>
References: <1272429119-12103-1-git-send-email-arve@android.com>
	<1272429119-12103-7-git-send-email-arve@android.com>
	<20100428194028.GA16389@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
Return-path: <linux-pm-bounces@lists.linux-foundation.org>
In-Reply-To: <20100428194028.GA16389@redhat.com>
List-Unsubscribe: <https://lists.linux-foundation.org/mailman/listinfo/linux-pm>,
	<mailto:linux-pm-request@lists.linux-foundation.org?subject=unsubscribe>
List-Archive: <http://lists.linux-foundation.org/pipermail/linux-pm>
List-Post: <mailto:linux-pm@lists.linux-foundation.org>
List-Help: <mailto:linux-pm-request@lists.linux-foundation.org?subject=help>
List-Subscribe: <https://lists.linux-foundation.org/mailman/listinfo/linux-pm>,
	<mailto:linux-pm-request@lists.linux-foundation.org?subject=subscribe>
Sender: linux-pm-bounces@lists.linux-foundation.org
Errors-To: linux-pm-bounces@lists.linux-foundation.org
To: Oleg Nesterov <oleg@redhat.com>, Arve =?iso-8859-1?q?Hj=F8nnev=E5g?= <arve@android.com>
Cc: Len Brown <len.brown@intel.com>, linux-kernel@vger.kernel.org, Tejun Heo <tj@kernel.org>, linux-pm@lists.linux-foundation.org
List-Id: linux-pm@vger.kernel.org

On Wednesday 28 April 2010, Oleg Nesterov wrote:
> On 04/27, Arve Hj=F8nnev=E5g 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 =3D queue_work(wq, &work->work);
> > +	if (ret)
> > +		work->active++;
> =

> why not
> =

> 	ret =3D 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.

Agreed.  Arve, any objections to doing that?

> 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...

It is.

> 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 =3D schedule_work(&work->work);
> =

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

Please see my reply to Tejun. :-)

Rafael