[PATCH] drm/virtio: fix vq wait_event condition

[Dave Airlie]

Reviewed-by: Dave Airlie <airlied at redhat.com>

On Fri., 20 Apr. 2018, 17:23 Gerd Hoffmann, <kraxel at redhat.com> wrote:

> On Tue, Apr 03, 2018 at 11:59:04AM +0200, Gerd Hoffmann wrote:
> > Wait until we have enough space in the virt queue to actually queue up
> > our request.  Avoids the guest spinning in case we have a non-zero
> > amount of free entries but not enough for the request.
>
> Ping airlied, can you please either pick it up or review so I can commit
> myself?
>
> thanks,
>   Gerd
>
> > Cc: stable at vger.kernel.org
> > Reported-by: Alain Magloire <amagloire at blackberry.com>
> > Signed-off-by: Gerd Hoffmann <kraxel at redhat.com>
> > ---
> >  drivers/gpu/drm/virtio/virtgpu_vq.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c
> b/drivers/gpu/drm/virtio/virtgpu_vq.c
> > index 48e4f1df6e..020070d483 100644
> > --- a/drivers/gpu/drm/virtio/virtgpu_vq.c
> > +++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
> > @@ -293,7 +293,7 @@ static int
> virtio_gpu_queue_ctrl_buffer_locked(struct virtio_gpu_device *vgdev,
> >       ret = virtqueue_add_sgs(vq, sgs, outcnt, incnt, vbuf, GFP_ATOMIC);
> >       if (ret == -ENOSPC) {
> >               spin_unlock(&vgdev->ctrlq.qlock);
> > -             wait_event(vgdev->ctrlq.ack_queue, vq->num_free);
> > +             wait_event(vgdev->ctrlq.ack_queue, vq->num_free >= outcnt
> + incnt);
> >               spin_lock(&vgdev->ctrlq.qlock);
> >               goto retry;
> >       } else {
> > @@ -368,7 +368,7 @@ static int virtio_gpu_queue_cursor(struct
> virtio_gpu_device *vgdev,
> >       ret = virtqueue_add_sgs(vq, sgs, outcnt, 0, vbuf, GFP_ATOMIC);
> >       if (ret == -ENOSPC) {
> >               spin_unlock(&vgdev->cursorq.qlock);
> > -             wait_event(vgdev->cursorq.ack_queue, vq->num_free);
> > +             wait_event(vgdev->cursorq.ack_queue, vq->num_free >=
> outcnt);
> >               spin_lock(&vgdev->cursorq.qlock);
> >               goto retry;
> >       } else {
> > --
> > 2.9.3
> >
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