Re: [PATCH net-next v7] vhost_net: avoid tx queue stuck when sendmsg fails

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Jan 15, 2021 at 12:46:20PM +0800, wangyunjian wrote:
> From: Yunjian Wang <wangyunjian@huawei.com>
> 
> Currently the driver doesn't drop a packet which can't be sent by tun
> (e.g bad packet). In this case, the driver will always process the
> same packet lead to the tx queue stuck.
> 
> To fix this issue:
> 1. in the case of persistent failure (e.g bad packet), the driver
>    can skip this descriptor by ignoring the error.
> 2. in the case of transient failure (e.g -ENOBUFS, -EAGAIN and -ENOMEM),
>    the driver schedules the worker to try again.
> 
> Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>

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

> ---
> v7:
>    * code rebase
> v6:
>    * update code styles and commit log
> ---
>  drivers/vhost/net.c | 26 ++++++++++++++------------
>  1 file changed, 14 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 3b744031ec8f..df82b124170e 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -828,14 +828,15 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
>  				msg.msg_flags &= ~MSG_MORE;
>  		}
>  
> -		/* TODO: Check specific error and bomb out unless ENOBUFS? */
>  		err = sock->ops->sendmsg(sock, &msg, len);
>  		if (unlikely(err < 0)) {
> -			vhost_discard_vq_desc(vq, 1);
> -			vhost_net_enable_vq(net, vq);
> -			break;
> -		}
> -		if (err != len)
> +			if (err == -EAGAIN || err == -ENOMEM || err == -ENOBUFS) {
> +				vhost_discard_vq_desc(vq, 1);
> +				vhost_net_enable_vq(net, vq);
> +				break;
> +			}
> +			pr_debug("Fail to send packet: err %d", err);
> +		} else if (unlikely(err != len))
>  			pr_debug("Truncated TX packet: len %d != %zd\n",
>  				 err, len);
>  done:
> @@ -924,7 +925,6 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
>  			msg.msg_flags &= ~MSG_MORE;
>  		}
>  
> -		/* TODO: Check specific error and bomb out unless ENOBUFS? */
>  		err = sock->ops->sendmsg(sock, &msg, len);
>  		if (unlikely(err < 0)) {
>  			if (zcopy_used) {
> @@ -933,11 +933,13 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
>  				nvq->upend_idx = ((unsigned)nvq->upend_idx - 1)
>  					% UIO_MAXIOV;
>  			}
> -			vhost_discard_vq_desc(vq, 1);
> -			vhost_net_enable_vq(net, vq);
> -			break;
> -		}
> -		if (err != len)
> +			if (err == -EAGAIN || err == -ENOMEM || err == -ENOBUFS) {
> +				vhost_discard_vq_desc(vq, 1);
> +				vhost_net_enable_vq(net, vq);
> +				break;
> +			}
> +			pr_debug("Fail to send packet: err %d", err);
> +		} else if (unlikely(err != len))
>  			pr_debug("Truncated TX packet: "
>  				 " len %d != %zd\n", err, len);
>  		if (!zcopy_used)
> -- 
> 2.23.0

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