On 4/12/22 11:53 AM, Jason Gunthorpe wrote:
When the open_device() op is called the container_users is incremented and held incremented until close_device(). Thus, so long as drivers call functions within their open_device()/close_device() region they do not need to worry about the container_users. These functions can all only be called between open_device()/close_device(): vfio_pin_pages() vfio_unpin_pages() vfio_dma_rw() vfio_register_notifier() vfio_unregister_notifier() So eliminate the calls to vfio_group_add_container_user() and add a simple WARN_ON to detect mis-use by drivers.
vfio_device_fops_release decrements dev->open_count immediately before calling dev->ops->close_device, which means we could enter close_device with a dev_count of 0.
Maybe vfio_device_fops_release should handle the same way as vfio_group_get_device_fd?
if (device->open_count == 1 && device->ops->close_device) device->ops->close_device(device); device->open_count--;
