netdev - [PATCH -next] virtio_net: Avoid loop in virtnet

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Message-Id: <1596339683-117617-1-git-send-email-wenan.mao@linux.alibaba.com>
Date:   Sun,  2 Aug 2020 11:41:23 +0800
From:   Mao Wenan <wenan.mao@...ux.alibaba.com>
To:     mst@...hat.com, jasowang@...hat.com, davem@...emloft.net,
        kuba@...nel.org
Cc:     netdev@...r.kernel.org, Mao Wenan <wenan.mao@...ux.alibaba.com>
Subject: [PATCH -next] virtio_net: Avoid loop in virtnet_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_napi_schedule //it will reschedule napi

Signed-off-by: Mao Wenan <wenan.mao@...ux.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