This patch checks the new event idx to make sure used event idx never goes back. This is used to synchronize the calls between virtqueue_enable_cb_delayed() and virtqueue_enable_cb(). Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx> --- drivers/virtio/virtio_ring.c | 7 +++++-- 1 files changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 3b1f89b..1b3929f 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -559,14 +559,17 @@ unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq) u16 last_used_idx; START_USE(vq); - + last_used_idx = vq->last_used_idx; /* We optimistically turn back on interrupts, then check if there was * more to do. */ /* Depending on the VIRTIO_RING_F_EVENT_IDX feature, we need to * either clear the flags bit or point the event index at the next * entry. Always do both to keep code simple. */ vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT; - vring_used_event(&vq->vring) = last_used_idx = vq->last_used_idx; + /* Make sure used event never go backwards */ + if (!vring_need_event(vring_used_event(&vq->vring), + vq->vring.avail->idx, last_used_idx)) + vring_used_event(&vq->vring) = last_used_idx; END_USE(vq); return last_used_idx; } -- 1.7.1 _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
