[PATCH -next] virtio_net: Avoid loop in virtnet_poll

[Mao Wenan]

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_napi_schedule //it will reschedule napi

Signed-off-by: Mao Wenan <wenan....@linux.alibaba.com>
---
 drivers/net/virtio_net.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index ba38765..a058da1 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -327,7 +327,8 @@ static void virtqueue_napi_complete(struct napi_struct 
*napi,
 
        opaque = virtqueue_enable_cb_prepare(vq);
        if (napi_complete_done(napi, processed)) {
-               if (unlikely(virtqueue_poll(vq, opaque)))
+               if (unlikely(virtqueue_poll(vq, opaque)) &&
+                   unlikely(!virtqueue_is_broken(vq)))
                        virtqueue_napi_schedule(napi, vq);
        } else {
                virtqueue_disable_cb(vq);
-- 
1.8.3.1