-----Original Message-----
From: Jason Wang [mailto:jasowang@redhat.com]
Sent: Thursday, December 24, 2020 1:56 PM
To: wangyunjian <redacted>
Cc: netdev@vger.kernel.org; mst@redhat.com;
willemdebruijn.kernel@gmail.com; virtualization@lists.linux-foundation.org;
Lilijun (Jerry) [off-list ref]; chenchanghu
[off-list ref]; xudingke [off-list ref]; huangbin (J)
[off-list ref]
Subject: Re: [PATCH net v4 2/2] vhost_net: fix tx queue stuck when sendmsg
fails


On 2020/12/24 下午12:37, wangyunjian wrote:

quoted

quoted

-----Original Message-----
From: Jason Wang [mailto:jasowang@redhat.com]
Sent: Thursday, December 24, 2020 11:10 AM
To: wangyunjian <redacted>; netdev@vger.kernel.org;
mst@redhat.com; willemdebruijn.kernel@gmail.com
Cc: virtualization@lists.linux-foundation.org; Lilijun (Jerry)
[off-list ref]; chenchanghu [off-list ref];
xudingke [off-list ref]; huangbin (J)
[off-list ref]
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:

quoted

From: Yunjian Wang <redacted>

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;

Yes, but the sock_alloc_send_pskb() returns - EAGAIN when no sndbuf space.
So there is need to check return value which is -EAGAIN or -ENOMEM or -

EAGAIN?

quoted

struct sk_buff *sock_alloc_send_pskb() { ...
	for (;;) {
...
		sk_set_bit(SOCKWQ_ASYNC_NOSPACE, sk);
		set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
		err = -EAGAIN;
		if (!timeo)
			goto failure;
...
	}
	skb = alloc_skb_with_frags(header_len, data_len, max_page_order,
				   errcode, sk->sk_allocation);
	if (skb)
		skb_set_owner_w(skb, sk);
	return skb;
...
	*errcode = err;
	return NULL;
}

-EAGAIN and -ENOBFS are fine. But I don't see how -ENOMEM can be returned.

The tun_build_skb() and tun_napi_alloc_frags() return -ENOMEM when memory
allocation fails.

Thanks

Thanks

quoted

quoted

Thanks

quoted

Fixes: 3a4d5c94e959 ("vhost_net: a kernel-level virtio server")
Signed-off-by: Yunjian Wang <redacted>
---
   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)

quoted

   				msg.msg_flags &= ~MSG_MORE;
   		}

-		/* TODO: Check specific error and bomb out unless ENOBUFS?

*/

quoted

quoted

quoted

   		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)

quoted

   			msg.msg_flags &= ~MSG_MORE;
   		}

-		/* TODO: Check specific error and bomb out unless ENOBUFS?

*/

quoted

quoted

quoted

   		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)

quoted

   				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)