Re: [PATCH 2/2] virtio_pmem: set device ready in probe()

["Michael S. Tsirkin" <mst@redhat.com>]

I think you should CC the maintainer, Pankaj Gupta.

On Mon, Jun 20, 2022 at 04:15:19PM +0800, Jason Wang wrote:
> The NVDIMM region could be available before the virtio_device_ready()
> that is called by virtio_dev_probe(). This means the driver tries to
> use device before DRIVER_OK which violates the spec, fixing this by
> set device ready before the nvdimm_pmem_region_create().
> 
> Note that this means the virtio_pmem_host_ack() could be triggered
> before the creation of the nd region, this is safe since the
> virtio_pmem_host_ack() since pmem_lock has been initialized and we
> check if we've added any buffer before trying to proceed.
> 
> Fixes 6e84200c0a29 ("virtio-pmem: Add virtio pmem driver")
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
>  drivers/nvdimm/virtio_pmem.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/nvdimm/virtio_pmem.c b/drivers/nvdimm/virtio_pmem.c
> index 48f8327d0431..173f2f5adaea 100644
> --- a/drivers/nvdimm/virtio_pmem.c
> +++ b/drivers/nvdimm/virtio_pmem.c
> @@ -84,6 +84,17 @@ static int virtio_pmem_probe(struct virtio_device *vdev)
>  	ndr_desc.provider_data = vdev;
>  	set_bit(ND_REGION_PAGEMAP, &ndr_desc.flags);
>  	set_bit(ND_REGION_ASYNC, &ndr_desc.flags);
> +	/*
> +	 * The NVDIMM region could be available before the
> +	 * virtio_device_ready() that is called by
> +	 * virtio_dev_probe(), so we set device ready here.
> +	 *

virtio_dev_probe is not to blame here, right?
I don't like copying its logic here as we won't remember to fix
it if we change virtio_dev_probe to e.g. not call virtio_device_ready.

is it nvdimm_pmem_region_create what makes it possible for
the region to become available?
Then "The NVDIMM region could become available immediately
after the call to nvdimm_pmem_region_create.
Tell device we are ready to handle this case."

> +	 * The callback - virtio_pmem_host_ack() is safe to be called
> +	 * before the nvdimm_pmem_region_create() since the pmem_lock
> +	 * has been initialized and legality of a used buffer is
> +	 * validated before moving forward.
> +	 */
> +	virtio_device_ready(vdev);
>  	nd_region = nvdimm_pmem_region_create(vpmem->nvdimm_bus, &ndr_desc);
>  	if (!nd_region) {
>  		dev_err(&vdev->dev, "failed to create nvdimm region\n");
> @@ -92,6 +103,7 @@ static int virtio_pmem_probe(struct virtio_device *vdev)
>  	}
>  	return 0;
>  out_nd:
> +	virtio_reset_device(vdev);


Does this fix cleanup too?

>  	nvdimm_bus_unregister(vpmem->nvdimm_bus);
>  out_vq:
>  	vdev->config->del_vqs(vdev);
> -- 
> 2.25.1