linux-kernel - Re: (resend) [PATCH v4 12/12] virtio: balloon: Add freeze, restore handlers to support S4

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Date:	Wed, 7 Dec 2011 16:09:41 +0530
From:	Amit Shah <amit.shah@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Virtualization List <virtualization@...ts.linux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>, levinsasha928@...il.com,
	linux-kernel@...r.kernel.org, Pavel Machek <pavel@....cz>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Len Brown <len.brown@...el.com>,
	linux-pm@...r.kernel.org
Subject: Re: (resend) [PATCH v4 12/12] virtio: balloon: Add freeze, restore
 handlers to support S4

On (Wed) 07 Dec 2011 [12:34:48], Michael S. Tsirkin wrote:
> On Wed, Dec 07, 2011 at 01:18:50AM +0530, Amit Shah wrote:
> > Now to not race with a host issuing ballooning requests while we are in
> > the process of freezing, we just exit from the vballoon kthread when the
> > processes are asked to freeze.  Upon thaw and restore, we re-start the
> > thread.
> 
> ...
> 
> > ---
> >  drivers/virtio/virtio_balloon.c |   79 ++++++++++++++++++++++++++++++++++++++-
> >  1 files changed, 78 insertions(+), 1 deletions(-)
> > 
> > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> > index 8bf99be..10ec638 100644
> > --- a/drivers/virtio/virtio_balloon.c
> > +++ b/drivers/virtio/virtio_balloon.c
> > @@ -258,7 +258,13 @@ static int balloon(void *_vballoon)
> >  	while (!kthread_should_stop()) {
> >  		s64 diff;
> >  
> > -		try_to_freeze();
> > +		/*
> > +		 * On suspend, we want to exit this thread.  We will
> > +		 * start a new thread on resume.
> > +		 */
> > +		if (freezing(current))
> > +			break;
> > +
> >  		wait_event_interruptible(vb->config_change,
> >  					 (diff = towards_target(vb)) != 0
> >  					 || vb->need_stats_update
> 
> ...
> 
> Note: this relies on kthreads being frozen before devices.
> Looking at kernel/power/hibernate.c this is the case,
> but I think we should add a comment to note this.

Yes, it does.  And for that reason, I mentioned that stopping the
thread doesn't buy us anything; I'll revert this change in the next
submission.

> Also Cc linux-pm crowd in case I got it wrong.

		Amit
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