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

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

On Mon, Jun 20, 2022 at 04:39:27PM +0800, Jason Wang wrote:
> 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

Oh, right.

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