Re: [PATCH 1/2] virtio: reset region cache when on queue deletion

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

On Thu, Jan 02, 2020 at 09:09:04AM +0200, Yuri Benditovich wrote:
> 
> 
> On Thu, Jan 2, 2020 at 1:50 AM Michael S. Tsirkin <mst@redhat.com> wrote:
> 
>     On Thu, Dec 26, 2019 at 11:29:50AM +0200, Yuri Benditovich wrote:
>     > On Thu, Dec 26, 2019 at 10:58 AM Jason Wang <jasowang@redhat.com> wrote:
>     > >
>     > >
>     > > On 2019/12/26 下午12:36, Yuri Benditovich wrote:
>     > > > https://bugzilla.redhat.com/show_bug.cgi?id=1708480
>     > > > Fix leak of region reference that prevents complete
>     > > > device deletion on hot unplug.
>     > >
>     > >
>     > > More information is needed here, the bug said only q35 can meet this
>     > > issue. What makes q35 different here?
>     > >
>     >
>     > I do not have any ready answer, I did not dig into it too much.
>     > Probably Michael Tsirkin or Paolo Bonzini can answer without digging.
> 
> 
> 
>     > >
>     > > >
>     > > > Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>
>     > > > ---
>     > > >   hw/virtio/virtio.c | 5 +++++
>     > > >   1 file changed, 5 insertions(+)
>     > > >
>     > > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
>     > > > index 04716b5f6c..baadec8abc 100644
>     > > > --- a/hw/virtio/virtio.c
>     > > > +++ b/hw/virtio/virtio.c
>     > > > @@ -2340,6 +2340,11 @@ void virtio_del_queue(VirtIODevice *vdev, int
>     n)
>     > > >       vdev->vq[n].vring.num_default = 0;
>     > > >       vdev->vq[n].handle_output = NULL;
>     > > >       vdev->vq[n].handle_aio_output = NULL;
>     > > > +    /*
>     > > > +     * with vring.num = 0 the queue will be ignored
>     > > > +     * in later loops of region cache reset
>     > > > +     */
>     > >
>     > >
>     > > I can't get the meaning of this comment.
>     > >
>     > > Thanks
>     > >
>     > >
>     > > > +    virtio_virtqueue_reset_region_cache(&vdev->vq[n]);
> 
> 
>     Do we need to drop this from virtio_device_free_virtqueues then?
> 
> 
> 
> Not mandatory. Repetitive  virtio_virtqueue_reset_region_cache does not do
> anything bad.
> Some of virtio devices do not do 'virtio_del_queue' at all. Currently 
> virtio_device_free_virtqueues resets region cache for them.
> IMO, not calling 'virtio_del_queue' is a bug, but not in the scope of current
> series, I'll take care of that later.

Maybe we should just del all queues in virtio_device_unrealize?
Will allow us to drop some logic tracking which vqs were created.


> 
>     > > >       g_free(vdev->vq[n].used_elems);
>     > > >   }
>     > > >
>     > >
> 
>