netdev - Re: [PATCH v4 13/25] virtio_console: enable VQs early

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Message-ID: <20141020133555.GA27111@redhat.com>
Date:	Mon, 20 Oct 2014 16:35:55 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Cornelia Huck <cornelia.huck@...ibm.com>
Cc:	Thomas Graf <tgraf@...g.ch>, linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org,
	linux-scsi@...r.kernel.org, linux-s390@...r.kernel.org,
	v9fs-developer@...ts.sourceforge.net, netdev@...r.kernel.org,
	kvm@...r.kernel.org, Amit Shah <amit.shah@...hat.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v4 13/25] virtio_console: enable VQs early

On Mon, Oct 20, 2014 at 02:42:23PM +0200, Cornelia Huck wrote:
> On Mon, 20 Oct 2014 13:07:50 +0100
> Thomas Graf <tgraf@...g.ch> wrote:
> 
> > On 10/13/14 at 10:50am, Michael S. Tsirkin wrote:
> > > virtio spec requires drivers to set DRIVER_OK before using VQs.
> > > This is set automatically after probe returns, virtio console violated this
> > > rule by adding inbufs, which causes the VQ to be used directly within
> > > probe.
> > > 
> > > To fix, call virtio_device_ready before using VQs.
> > > 
> > > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> > > ---
> > >  drivers/char/virtio_console.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > > 
> > > diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> > > index b585b47..6ebe8f6 100644
> > > --- a/drivers/char/virtio_console.c
> > > +++ b/drivers/char/virtio_console.c
> > > @@ -1449,6 +1449,8 @@ static int add_port(struct ports_device *portdev, u32 id)
> > >  	spin_lock_init(&port->outvq_lock);
> > >  	init_waitqueue_head(&port->waitqueue);
> > >  
> > > +	virtio_device_ready(portdev->vdev);
> > > +
> > >  	/* Fill the in_vq with buffers so the host can send us data. */
> > >  	nr_added_bufs = fill_queue(port->in_vq, &port->inbuf_lock);
> > >  	if (!nr_added_bufs) {
> > 
> > Seems like probe and add_port() now both set VIRTIO_CONFIG_S_DRIVER_OK
> 
> I think we need to set this in the probe function instead, otherwise we
> fail for multiqueue (which also wants to use the control queue early).
> 
> Completely untested patch below; I can send this with proper s-o-b if
> it helps.
> 
> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> index bfa6400..cf7a561 100644
> --- a/drivers/char/virtio_console.c
> +++ b/drivers/char/virtio_console.c
> @@ -1449,8 +1449,6 @@ static int add_port(struct ports_device *portdev, u32 id)
>  	spin_lock_init(&port->outvq_lock);
>  	init_waitqueue_head(&port->waitqueue);
>  
> -	virtio_device_ready(portdev->vdev);
> -
>  	/* Fill the in_vq with buffers so the host can send us data. */
>  	nr_added_bufs = fill_queue(port->in_vq, &port->inbuf_lock);
>  	if (!nr_added_bufs) {
> @@ -2026,6 +2024,8 @@ static int virtcons_probe(struct virtio_device *vdev)
>  	spin_lock_init(&portdev->ports_lock);
>  	INIT_LIST_HEAD(&portdev->ports);
>  
> +	virtio_device_ready(portdev->vdev);
> +
>  	if (multiport) {
>  		unsigned int nr_added_bufs;
>  

I wanted to set DRIVER_OK as late as possible, to both reduce
the chance it can fail after DRIVER_OK and to reduce  the risk of
introducing a regression since old qemu might only start sending
interrupts after DRIVER_OK is set.

So I wanted everything completely initialized before DRIVER_OK.

You patch makes sense to me since nothing can fail,
and we won't get interrupts before we add inbufs.

Reviewed-by: Michael S. Tsirkin <mst@...hat.com>

Testig will report shortly, pls send with sob line.

-- 
MST
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