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--;