* [PATCH -next] virtio_net: Avoid loop in virtnet_poll
@ 2020-08-02 3:41 Mao Wenan
2020-08-02 4:40 ` Michael S. Tsirkin
0 siblings, 1 reply; 2+ messages in thread
From: Mao Wenan @ 2020-08-02 3:41 UTC (permalink / raw)
To: mst, jasowang, davem, kuba; +Cc: netdev, 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.mao@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
^ permalink raw reply related [flat|nested] 2+ messages in thread* Re: [PATCH -next] virtio_net: Avoid loop in virtnet_poll
2020-08-02 3:41 [PATCH -next] virtio_net: Avoid loop in virtnet_poll Mao Wenan
@ 2020-08-02 4:40 ` Michael S. Tsirkin
0 siblings, 0 replies; 2+ messages in thread
From: Michael S. Tsirkin @ 2020-08-02 4:40 UTC (permalink / raw)
To: Mao Wenan; +Cc: jasowang, davem, kuba, netdev
On Sun, Aug 02, 2020 at 11:41:23AM +0800, Mao Wenan wrote:
> 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@linux.alibaba.com>
I think it's more a bug in virtqueue_poll : virtqueue_get_buf reports
NULL on broken, so virtqueue_poll should report false for consistency.
> ---
> 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
^ permalink raw reply [flat|nested] 2+ messages in thread
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2020-08-02 4:40 ` Michael S. Tsirkin
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