Re: [PATCH net 1/2] vhost-net: unbreak busy polling

Michael S. Tsirkin
2025-09-12T08:51:16Z

On Fri, Sep 12, 2025 at 04:26:57PM +0800, Jason Wang wrote:
> Commit 67a873df0c41 ("vhost: basic in order support") pass the number
> of used elem to vhost_net_rx_peek_head_len() to make sure it can
> signal the used correctly before trying to do busy polling. But it
> forgets to clear the count, this would cause the count run out of sync
> with handle_rx() and break the busy polling.
>
> Fixing this by passing the pointer of the count and clearing it after
> the signaling the used.
>
> Cc: stable@vger.kernel.org
> Fixes: 67a873df0c41 ("vhost: basic in order support")
> Signed-off-by: Jason Wang <jasowang@redhat.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

> ---
> drivers/vhost/net.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index c6508fe0d5c8..16e39f3ab956 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -1014,7 +1014,7 @@ static int peek_head_len(struct vhost_net_virtqueue *rvq, struct sock *sk)
> }
>
> static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk,
> - bool *busyloop_intr, unsigned int count)
> + bool *busyloop_intr, unsigned int *count)
> {
> struct vhost_net_virtqueue *rnvq = &net->vqs[VHOST_NET_VQ_RX];
> struct vhost_net_virtqueue *tnvq = &net->vqs[VHOST_NET_VQ_TX];
> @@ -1024,7 +1024,8 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk,
>
> if (!len && rvq->busyloop_timeout) {
> /* Flush batched heads first */
> - vhost_net_signal_used(rnvq, count);
> + vhost_net_signal_used(rnvq, *count);
> + *count = 0;
> /* Both tx vq and rx socket were polled here */
> vhost_net_busy_poll(net, rvq, tvq, busyloop_intr, true);
>
> @@ -1180,7 +1181,7 @@ static void handle_rx(struct vhost_net *net)
>
> do {
> sock_len = vhost_net_rx_peek_head_len(net, sock->sk,
> - &busyloop_intr, count);
> + &busyloop_intr, &count);
> if (!sock_len)
> break;
> sock_len += sock_hlen;
> --
> 2.34.1