netdev - Re: [PATCH net v4 2/2] vhost_net: fix tx queue stuck when sendmsg fails

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Date:   Thu, 24 Dec 2020 11:10:25 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     wangyunjian <wangyunjian@...wei.com>, netdev@...r.kernel.org,
        mst@...hat.com, willemdebruijn.kernel@...il.com
Cc:     virtualization@...ts.linux-foundation.org,
        jerry.lilijun@...wei.com, chenchanghu@...wei.com,
        xudingke@...wei.com, brian.huangbin@...wei.com
Subject: Re: [PATCH net v4 2/2] vhost_net: fix tx queue stuck when sendmsg
 fails


On 2020/12/24 上午10:25, wangyunjian wrote:
> From: Yunjian Wang <wangyunjian@...wei.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 -EAGAIN and -ENOMEM), the
> driver schedules the worker to try again.


I might be wrong but looking at alloc_skb_with_frags(), it returns 
-ENOBUFS actually:

     *errcode = -ENOBUFS;
     skb = alloc_skb(header_len, gfp_mask);
     if (!skb)
         return NULL;

Thanks


>
> Fixes: 3a4d5c94e959 ("vhost_net: a kernel-level virtio server")
> Signed-off-by: Yunjian Wang <wangyunjian@...wei.com>
> ---
>   drivers/vhost/net.c | 16 ++++++++--------
>   1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index c8784dfafdd7..e76245daa7f6 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -827,14 +827,13 @@ 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)) {
> +		if (unlikely(err == -EAGAIN || err == -ENOMEM)) {
>   			vhost_discard_vq_desc(vq, 1);
>   			vhost_net_enable_vq(net, vq);
>   			break;
>   		}
> -		if (err != len)
> +		if (err >= 0 && err != len)
>   			pr_debug("Truncated TX packet: len %d != %zd\n",
>   				 err, len);
>   done:
> @@ -922,7 +921,6 @@ 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) {
> @@ -931,11 +929,13 @@ 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 == -EAGAIN || err == -ENOMEM) {
> +				vhost_discard_vq_desc(vq, 1);
> +				vhost_net_enable_vq(net, vq);
> +				break;
> +			}
>   		}
> -		if (err != len)
> +		if (err >= 0 && err != len)
>   			pr_debug("Truncated TX packet: "
>   				 " len %d != %zd\n", err, len);
>   		if (!zcopy_used)