linux-kernel - Re: [PATCH v3 09/11] virtio: net: Add freeze, restore handlers to support S4

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Message-ID: <20111117123311.GE19682@redhat.com>
Date:	Thu, 17 Nov 2011 14:33:11 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Amit Shah <amit.shah@...hat.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Virtualization List <virtualization@...ts.linux-foundation.org>,
	levinsasha928@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 09/11] virtio: net: Add freeze, restore handlers to
 support S4

On Thu, Nov 17, 2011 at 05:57:06PM +0530, Amit Shah wrote:
> On (Thu) 17 Nov 2011 [14:19:09], Michael S. Tsirkin wrote:
> > On Thu, Nov 17, 2011 at 05:27:40PM +0530, Amit Shah wrote:
> 
> > > +#ifdef CONFIG_PM
> > > +static int virtnet_freeze(struct virtio_device *vdev)
> > > +{
> > > +	struct virtnet_info *vi = vdev->priv;
> > > +
> > > +	netif_device_detach(vi->dev);
> > > +	remove_vq_common(vi);
> > 
> > This stops TX in progress, if any, but not RX
> > which might use the RX VQ. Then remove_vq_common
> > might delete this VQ while it's still in use.
> > 
> > So I think we need to call something like napi_disable.
> > However, the subtle twist is that we need to call that
> > *after interrupts have been disabled*.
> > Otherwise we might schedule another napi callback.
> 
> resetting the vqs will mean the host won't pass us any data in the
> vqs.  Plus we're removing the vqs altogether.  Also, we're disabling
> the pci device in virtio_pci.c, so all of these actions will take
> care of that, isn't it?

I don't think so.

> In addition, once the vqs are taken off, there's no chance for any
> other rx to happen, so napi_disable() after plugging off vqs doesn't
> make sense.
> 
> 		Amit


Yes but napi might have been scheduled before remove_vq_common was
called, and run afterwards.

-- 
MST
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