Re: [PATCH -next v3] virtio_ring: Avoid loop when vq is broken in virtqueue_poll

The loop may exist if vq->broken is true,
virtqueue_get_buf_ctx_packed or virtqueue_get_buf_ctx_split
will return NULL, so virtnet_poll will reschedule napi to
receive packet, it will lead cpu usage(si) to 100%.

call trace as below:
virtnet_poll
	virtnet_receive
		virtqueue_get_buf_ctx
			virtqueue_get_buf_ctx_packed
			virtqueue_get_buf_ctx_split
	virtqueue_napi_complete
		virtqueue_poll           //return true
		virtqueue_napi_schedule //it will reschedule napi

to fix this, return false if vq is broken in virtqueue_poll.

Signed-off-by: Mao Wenan <redacted>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
---
  v2->v3: change subject, original is : "virtio_net: Avoid loop in virtnet_poll"
  v1->v2: fix it in virtqueue_poll suggested by Michael S. Tsirkin [off-list ref]
  drivers/virtio/virtio_ring.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 58b96ba..4f7c73e 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c

@@ -1960,6 +1960,9 @@ bool virtqueue_poll(struct virtqueue *_vq, unsigned last_used_idx)
  {
  	struct vring_virtqueue *vq = to_vvq(_vq);
  
+	if (unlikely(vq->broken))
+		return false;
+
  	virtio_mb(vq->weak_barriers);
  	return vq->packed_ring ? virtqueue_poll_packed(_vq, last_used_idx) :
  				 virtqueue_poll_split(_vq, last_used_idx);