Linux Virtualization - Nov 2017 - [PATCH] virtio: release virtio index when fail to device_register

index can be reused by other virtio device.

Signed-off-by: weiping zhang <zhangweiping at didichuxing.com>
---
 drivers/virtio/virtio.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 48230a5..bf7ff39 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -333,6 +333,8 @@ int register_virtio_device(struct virtio_device *dev)
 	/* device_register() causes the bus infrastructure to look for a
 	 * matching driver. */
 	err = device_register(&dev->dev);
+	if (err)
+		ida_simple_remove(&virtio_index_ida, dev->index);
 out:
 	if (err)
 		virtio_add_status(dev, VIRTIO_CONFIG_S_FAILED);
-- 
2.9.4

On Wed, 29 Nov 2017 09:23:01 +0800
weiping zhang <zwp10758 at gmail.com> wrote:
> index can be reused by other virtio device.
> 
> Signed-off-by: weiping zhang <zhangweiping at didichuxing.com>
Reviewed-by: Cornelia Huck <cohuck at redhat.com>
> ---
>  drivers/virtio/virtio.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index 48230a5..bf7ff39 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -333,6 +333,8 @@ int register_virtio_device(struct virtio_device *dev)
>  	/* device_register() causes the bus infrastructure to look for a
>  	 * matching driver. */
>  	err = device_register(&dev->dev);
> +	if (err)
> +		ida_simple_remove(&virtio_index_ida, dev->index);
>  out:
>  	if (err)
>  		virtio_add_status(dev, VIRTIO_CONFIG_S_FAILED);
I think your patch is correct (giving up the index if we failed to
register), but this made me look at our error handling if a virtio
device failed to register.

We hold an extra reference to the struct device, even after a failed
register, and it is the responsibility of the caller to give up that
reference once no longer needed. As callers toregister_virtio_device()
embed the struct virtio_device, it needs to be their responsibility.
Looking at the existing callers,

- ccw does a put_device
- pci, mmio and remoteproc do nothing, causing a leak
- vop does a free on the embedding structure, which is a big no-no

Thoughts?

On Wed, Nov 29, 2017 at 09:23:01AM +0800, weiping zhang
wrote:
> index can be reused by other virtio device.
> 
> Signed-off-by: weiping zhang <zhangweiping at didichuxing.com>
Thanks!
I've queued this up, this is needed on stable as well.

> ---
>  drivers/virtio/virtio.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index 48230a5..bf7ff39 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -333,6 +333,8 @@ int register_virtio_device(struct virtio_device *dev)
>  	/* device_register() causes the bus infrastructure to look for a
>  	 * matching driver. */
>  	err = device_register(&dev->dev);
> +	if (err)
> +		ida_simple_remove(&virtio_index_ida, dev->index);
>  out:
>  	if (err)
>  		virtio_add_status(dev, VIRTIO_CONFIG_S_FAILED);
> -- 
> 2.9.4

On Wed, Nov 29, 2017 at 10:50:44AM +0100, Cornelia Huck
wrote:
> On Wed, 29 Nov 2017 09:23:01 +0800
> weiping zhang <zwp10758 at gmail.com> wrote:
> 
> > index can be reused by other virtio device.
> > 
> > Signed-off-by: weiping zhang <zhangweiping at didichuxing.com>
> 
> Reviewed-by: Cornelia Huck <cohuck at redhat.com>
> 
> > ---
> >  drivers/virtio/virtio.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> > index 48230a5..bf7ff39 100644
> > --- a/drivers/virtio/virtio.c
> > +++ b/drivers/virtio/virtio.c
> > @@ -333,6 +333,8 @@ int register_virtio_device(struct virtio_device
*dev)
> >  	/* device_register() causes the bus infrastructure to look for a
> >  	 * matching driver. */
> >  	err = device_register(&dev->dev);
> > +	if (err)
> > +		ida_simple_remove(&virtio_index_ida, dev->index);
> >  out:
> >  	if (err)
> >  		virtio_add_status(dev, VIRTIO_CONFIG_S_FAILED);
> 
> I think your patch is correct (giving up the index if we failed to
> register), but this made me look at our error handling if a virtio
> device failed to register.
> 
> We hold an extra reference to the struct device, even after a failed
> register, and it is the responsibility of the caller to give up that
> reference once no longer needed. As callers toregister_virtio_device()
> embed the struct virtio_device, it needs to be their responsibility.
> Looking at the existing callers,
> 
> - ccw does a put_device
> - pci, mmio and remoteproc do nothing, causing a leak
> - vop does a free on the embedding structure, which is a big no-no
> 
> Thoughts?
Sorry to relay late and thanks for your review.
Do you mean the "extra reference to the struct device" caused by the
following code?
 
err = device_register(&dev->dev);
	device_add(dev)
		get_device(dev)
If I'm understand right, I think there is no extra reference if we fail
virtio_register_device, because if device_register we don't get a
reference.

--
Thanks
weiping