Re: [PATCH v4 1/3] vfio: Fix container device registration life cycle

[Alex Williamson <alex.williamson@redhat.com>]

On Fri,  4 Nov 2022 12:57:25 -0700
Anthony DeRossi <ajderossi@gmail.com> wrote:

> In vfio_device_open(), vfio_container_device_register() is always called
> when open_count == 1. On error, vfio_device_container_unregister() is
> only called when open_count == 1 and close_device is set. This leaks a
> registration for devices without a close_device implementation.
> 
> In vfio_device_fops_release(), vfio_device_container_unregister() is
> called unconditionally. This can cause a device to be unregistered
> multiple times.
> 
> Treating container device registration/unregistration uniformly (always
> when open_count == 1) fixes both issues.

Good catch, I see that Jason does subtly fix this in "vfio: Move
vfio_device driver open/close code to a function", but I'd rather see
it more overtly fixed in a discrete patch like this.  All "real"
drivers provide a close_device callback, but mdpy and mtty do not.
Thanks,

Alex

> Fixes: ce4b4657ff18 ("vfio: Replace the DMA unmapping notifier with a callback")
> Signed-off-by: Anthony DeRossi <ajderossi@gmail.com>
> ---
>  drivers/vfio/vfio_main.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index 2d168793d4e1..9a4af880e941 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -801,8 +801,9 @@ static struct file *vfio_device_open(struct vfio_device *device)
>  err_close_device:
>  	mutex_lock(&device->dev_set->lock);
>  	mutex_lock(&device->group->group_lock);
> -	if (device->open_count == 1 && device->ops->close_device) {
> -		device->ops->close_device(device);
> +	if (device->open_count == 1) {
> +		if (device->ops->close_device)
> +			device->ops->close_device(device);
>  
>  		vfio_device_container_unregister(device);
>  	}
> @@ -1017,10 +1018,12 @@ static int vfio_device_fops_release(struct inode *inode, struct file *filep)
>  	mutex_lock(&device->dev_set->lock);
>  	vfio_assert_device_open(device);
>  	mutex_lock(&device->group->group_lock);
> -	if (device->open_count == 1 && device->ops->close_device)
> -		device->ops->close_device(device);
> +	if (device->open_count == 1) {
> +		if (device->ops->close_device)
> +			device->ops->close_device(device);
>  
> -	vfio_device_container_unregister(device);
> +		vfio_device_container_unregister(device);
> +	}
>  	mutex_unlock(&device->group->group_lock);
>  	device->open_count--;
>  	if (device->open_count == 0)