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

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

2017-12-02 0:55 GMT+08:00 weiping zhang <zwp10758 at
gmail.com>:
> 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.
I go through these callers,  virtio_mmio_probe should do more cleanup.
I'll sent a patch fix that.
> --
> Thanks
> weiping

On Sat, 2 Dec 2017 00:55:39 +0800
weiping zhang <zwp10758 at gmail.com> wrote:
> On Wed, Nov 29, 2017 at 10:50:44AM +0100, Cornelia Huck wrote:
> > 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.
The device_initialize() already gives you a reference. If device_add()
fails, it has cleaned up any additional reference it might have
obtained, but the initial reference is still there and needs to be
released by the caller.

2017-12-04 17:38 GMT+08:00 Cornelia Huck <cohuck at
redhat.com>:
> On Sat, 2 Dec 2017 00:55:39 +0800
> weiping zhang <zwp10758 at gmail.com> wrote:
>
>> On Wed, Nov 29, 2017 at 10:50:44AM +0100, Cornelia Huck wrote:
>
>> > 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.
>
> The device_initialize() already gives you a reference. If device_add()
> fails, it has cleaned up any additional reference it might have
> obtained, but the initial reference is still there and needs to be
> released by the caller.
Thanks your clarify, I also notice the comments at device_register,
device_initialize, device_add,

 * NOTE: _Never_ directly free @dev after calling this function, even
 * if it returned an error! Always use put_device() to give up the
 * reference initialized in this function instead.

--
Thanks
weiping