[PATCH] drm/virtio: fix vq wait_event condition

[Gerd Hoffmann]

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.

Cc: sta...@vger.kernel.org
Reported-by: Alain Magloire <amaglo...@blackberry.com>
Signed-off-by: Gerd Hoffmann <kra...@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