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

[Jason Wang <jasowang@redhat.com>]

On Mon, Jun 20, 2022 at 4:32 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> I think you should CC the maintainer, Pankaj Gupta.

Yes, I miss him accidentally.

>
> 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?

Yes and actually it's not to blame, it just describes what can happen now.

> 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?

I think so.

> 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."

That's fine.

>
> > +      * 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?

Not sure I get this, we make the device ready before
nvdimm_pmem_region_create(), so we need to reset if
nvdimm_pmem_region_create() fails?

Thanks

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