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    Subject[PATCH 4.16 030/113] drm/virtio: fix vq wait_event condition
    Date
    4.16-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Gerd Hoffmann <kraxel@redhat.com>

    commit d02d270014f70dcab0117776b81a37b6fca745ae upstream.

    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: stable@vger.kernel.org
    Reported-by: Alain Magloire <amagloire@blackberry.com>
    Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
    Reviewed-by: Dave Airlie <airlied@redhat.com>
    Link: http://patchwork.freedesktop.org/patch/msgid/20180403095904.11152-1-kraxel@redhat.com
    Signed-off-by: Sean Paul <seanpaul@chromium.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/gpu/drm/virtio/virtgpu_vq.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/drivers/gpu/drm/virtio/virtgpu_vq.c
    +++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
    @@ -291,7 +291,7 @@ retry:
    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 {
    @@ -366,7 +366,7 @@ retry:
    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 {

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