On Wed, Jun 22, 2022 at 2:29 PM Michael S. Tsirkin <[email protected]> wrote:
>
> On Tue, Jun 21, 2022 at 03:38:35PM -0700, Dan Williams wrote:
> > 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().
> >
> > Can you clarify the failure path. What race is virtio_device_ready()
> > losing?
> >
> > >
> > > 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.
> >
> > I got a little bit lost with the usage of "we" here. Can you clarify
> > which function / context is making which guarantee?
> >
> > >
> > > Fixes 6e84200c0a29 ("virtio-pmem: Add virtio pmem driver")
> > > Signed-off-by: Jason Wang <[email protected]>
> > > ---
> > > 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.
> > > + *
> > > + * 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.
> >
> > This comment feels like changelog material. Just document why
> > virtio_device_ready() must be called before device_add() of the
> > nd_region.
>
> Agree here. More specifically if you are documenting why is it
> safe to invoke each callback then that belongs to the callback itself.
Ok, so I will move it to the callback and leave a simple comment like
" See comment in virtio_pmem_host_ack(), it is safe to be called
before nvdimm_pmem_region_create()"
Thanks
>
> > > + */
> > > + 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);
> > > nvdimm_bus_unregister(vpmem->nvdimm_bus);
> > > out_vq:
> > > vdev->config->del_vqs(vdev);
> > > --
> > > 2.25.1
> > >
>
