Re: [PATCH] virtio_console: free unused buffers with virtio port

Pankaj Gupta
2019-03-11T06:53:33Z

> >
> > Hello Michael,
> >
> > Thanks for your reply.
> >
> > >
> > > On Mon, Mar 04, 2019 at 06:35:11PM +0530, Pankaj Gupta wrote:
> > > > The commit a7a69ec0d8e4 ("virtio_console: free buffers after reset")
> > > > deffered detaching of unused buffer to virtio device unplug time.
> > > >
> > > > This causes unplug/replug of single port in virtio device with an
> > > > error "Error allocating inbufs\n". As we don't free the unused
> > > > buffers
> > > > attached with the port. Re-plug the same port tries to allocate new
> > > > buffers in virtqueue and results in this error if queue is full.
>
> That's the basic issue, isn't it? Why aren't we
> reusing buffers that are already there?

I think that that's how initial design has been. Will see if I can fix this.

>
>
> > > >
> > > > This patch removes the unused buffers in vq's when we unplug the
> > > > port.
> > > > This is the best we can do as we cannot call device_reset because
> > > > virtio
> > > > device is still active. This was the working behaviour before the
> > > > change
> > > > introduced in commit b3258ff1d6.
> > > >
> > > > Reported-by: Xiaohui Li <xiaohli@redhat.com>
> > > > Fixes: b3258ff1d6 ("virtio_console: free buffers after reset")
> > > > Signed-off-by: Pankaj Gupta <pagupta@redhat.com>
> > >
> > > I think if you do this you need to add support
> > > in the packed ring.
> >
> > o.k. I will look at the implementation details for "support
> > of packed ring" for virtio_console. This will take some time.
> >
> > Meanwhile "virtio_console" port hotplug/unplug is broken in upstream.
> > Can we accept this patch as it fixes the upstream and together
> > with parent patch(b3258ff1d6) does nice cleanups as well.
> >
> > Thanks,
> > Pankaj
>
> Sorry, no - I don't think we should fix one configuration by breaking the
> other.
> If you want to go back, then that's a spec violation, but I guess we can
> fix the spec to match. OK, but code-wise if you call
> virtqueue_detach_unused_buf without device reset then you need to teach
> packed ring code to support that.

o.k. Will look at this.

Thanks for the pointers.

Thanks,
Pankaj

>
>
>
> > >
> > > > ---
> > > > drivers/char/virtio_console.c | 14 +++++++++++---
> > > > 1 file changed, 11 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/drivers/char/virtio_console.c
> > > > b/drivers/char/virtio_console.c
> > > > index fbeb71953526..5fbf2ac73111 100644
> > > > --- a/drivers/char/virtio_console.c
> > > > +++ b/drivers/char/virtio_console.c
> > > > @@ -1506,15 +1506,25 @@ static void remove_port(struct kref *kref)
> > > > kfree(port);
> > > > }
> > > >
> > > > +static void remove_unused_bufs(struct virtqueue *vq)
> > > > +{
> > > > + struct port_buffer *buf;
> > > > +
> > > > + while ((buf = virtqueue_detach_unused_buf(vq)))
> > > > + free_buf(buf, true);
> > > > +}
> > > > +
> > > > static void remove_port_data(struct port *port)
> > > > {
> > > > spin_lock_irq(&port->inbuf_lock);
> > > > /* Remove unused data this port might have received. */
> > > > discard_port_data(port);
> > > > + remove_unused_bufs(port->in_vq);
> > > > spin_unlock_irq(&port->inbuf_lock);
> > > >
> > > > spin_lock_irq(&port->outvq_lock);
> > > > reclaim_consumed_buffers(port);
> > > > + remove_unused_bufs(port->out_vq);
> > > > spin_unlock_irq(&port->outvq_lock);
> > > > }
> > > >
> > > > @@ -1950,11 +1960,9 @@ static void remove_vqs(struct ports_device
> > > > *portdev)
> > > > struct virtqueue *vq;
> > > >
> > > > virtio_device_for_each_vq(portdev->vdev, vq) {
> > > > - struct port_buffer *buf;
> > > >
> > > > flush_bufs(vq, true);
> > > > - while ((buf = virtqueue_detach_unused_buf(vq)))
> > > > - free_buf(buf, true);
> > > > + remove_unused_bufs(vq);
> > > > }
> > > > portdev->vdev->config->del_vqs(portdev->vdev);
> > > > kfree(portdev->in_vqs);
> > > > --
> > > > 2.20.1
> > >
>