Re: [dpdk-dev] [PATCH] vhost: fix notification for packed ring

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

On Thu, Oct 11, 2018 at 09:34:06PM +0800, Jason Wang wrote:
> 
> 
> On 2018年10月11日 21:06, Tiwei Bie wrote:
> > The notification can't be disabled in packed ring when
> > application tries to disable notification, because the
> > device event flags field is overwritten by an unexpected
> > value. This patch fixes this issue.
> > 
> > Fixes: b1cce26af1dc ("vhost: add notification for packed ring")
> > Cc: stable@dpdk.org
> > 
> > Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
> > ---
> >   lib/librte_vhost/vhost.c | 7 +++++--
> >   1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
> > index e62f4c594..c9270bdec 100644
> > --- a/lib/librte_vhost/vhost.c
> > +++ b/lib/librte_vhost/vhost.c
> > @@ -667,8 +667,10 @@ vhost_enable_notify_packed(struct virtio_net *dev,
> >   {
> >   	uint16_t flags;
> > -	if (!enable)
> > -		vq->device_event->flags = VRING_EVENT_F_DISABLE;
> > +	if (!enable) {
> > +		flags = VRING_EVENT_F_DISABLE;
> > +		goto out;
> > +	}
> >   	flags = VRING_EVENT_F_ENABLE;
> >   	if (dev->features & (1ULL << VIRTIO_RING_F_EVENT_IDX)) {
> > @@ -677,6 +679,7 @@ vhost_enable_notify_packed(struct virtio_net *dev,
> >   			vq->avail_wrap_counter << 15;
> >   	}
> > +out:
> >   	rte_smp_wmb();
> 
> It looks to me the barrier is even not needed for !enable.
> 
> Thanks

Good point, I agree.
Besides that

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>



> >   	vq->device_event->flags = flags;