From: Mao Wenan <wenan....@linux.alibaba.com>

[ Upstream commit 481a0d7422db26fb63e2d64f0652667a5c6d0f3e ]

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 <wenan....@linux.alibaba.com>
Acked-by: Michael S. Tsirkin <m...@redhat.com>
Link: 
https://lore.kernel.org/r/1596354249-96204-1-git-send-email-wenan....@linux.alibaba.com
Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
Acked-by: Jason Wang <jasow...@redhat.com>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
 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 b82bb0b081615..51278f8bd3ab3 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -829,6 +829,9 @@ 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 (u16)last_used_idx != virtio16_to_cpu(_vq->vdev, 
vq->vring.used->idx);
 }
-- 
2.25.1

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