linux-kernel - Re: [PATCH v4 06/12] virtio: blk: Add freeze, restore handlers to support S4

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Message-ID: <20111207105647.GI4651@amit-x200.redhat.com>
Date:	Wed, 7 Dec 2011 16:26:47 +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
Subject: Re: [PATCH v4 06/12] virtio: blk: Add freeze, restore handlers to
 support S4

On (Wed) 07 Dec 2011 [12:37:02], Michael S. Tsirkin wrote:
> On Wed, Dec 07, 2011 at 01:18:44AM +0530, Amit Shah wrote:
> > Delete the vq and flush any pending requests from the block queue on the
> > freeze callback to prepare for hibernation.
> > 
> > Re-create the vq in the restore callback to resume normal function.
> > 
> > Signed-off-by: Amit Shah <amit.shah@...hat.com>
> > ---
> >  drivers/block/virtio_blk.c |   38 ++++++++++++++++++++++++++++++++++++++
> >  1 files changed, 38 insertions(+), 0 deletions(-)
> > 
> > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > index 467f218..a9147a6 100644
> > --- a/drivers/block/virtio_blk.c
> > +++ b/drivers/block/virtio_blk.c
> > @@ -568,6 +568,40 @@ static void __devexit virtblk_remove(struct virtio_device *vdev)
> >  	ida_simple_remove(&vd_index_ida, index);
> >  }
> >  
> > +#ifdef CONFIG_PM
> > +static int virtblk_freeze(struct virtio_device *vdev)
> > +{
> > +	struct virtio_blk *vblk = vdev->priv;
> > +
> > +	/* Ensure we don't receive any more interrupts */
> > +	vdev->config->reset(vdev);
> > +
> > +	flush_work(&vblk->config_work);
> 
> It bothers me that config work can be running
> after reset here. If it does, it will not get sane
> values from reading config.

Why so?

The reset only ensures the host doesn't write anything more, isn't it?
Why would the values be affected?

> Also, can there be stuff in the reqs list?
> If yes is this a problem?

Should be all cleared by the two commands below.  At least that's my
expectation.  If not, let me know!

> > +	spin_lock_irq(vblk->disk->queue->queue_lock);
> > +	blk_stop_queue(vblk->disk->queue);
> > +	spin_unlock_irq(vblk->disk->queue->queue_lock);
> > +	blk_sync_queue(vblk->disk->queue);
> > +
> > +	vdev->config->del_vqs(vdev);
> > +	return 0;
> > +}
> > +
> 
> Thinking about it, looks like there's a bug in
> virtblk_remove: if we get a config change after
> flush_work we schedule another work.
> That's a problem for sure as structure is removed.

Yep, it is a potential issue.

		Amit
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