On Thu, Nov 30, 2017 at 10:46:17AM +0800, Jason Wang wrote: > > > On 2017年11月29日 23:31, Michael S. Tsirkin wrote: > > On Wed, Nov 29, 2017 at 09:23:24AM -0500,wexu@xxxxxxxxxx wrote: > > > From: Wei Xu<wexu@xxxxxxxxxx> > > > > > > Matthew found a roughly 40% tcp throughput regression with commit > > > c67df11f(vhost_net: try batch dequing from skb array) as discussed > > > in the following thread: > > > https://www.mail-archive.com/netdev@xxxxxxxxxxxxxxx/msg187936.html > > > > > > Eventually we figured out that it was a skb leak in handle_rx() > > > when sending packets to the VM. This usually happens when a guest > > > can not drain out vq as fast as vhost fills in, afterwards it sets > > > off the traffic jam and leaks skb(s) which occurs as no headcount > > > to send on the vq from vhost side. > > > > > > This can be avoided by making sure we have got enough headcount > > > before actually consuming a skb from the batched rx array while > > > transmitting, which is simply done by moving checking the zero > > > headcount a bit ahead. > > > > > > Also strengthen the small possibility of leak in case of recvmsg() > > > fails by freeing the skb. > > > > > > Signed-off-by: Wei Xu<wexu@xxxxxxxxxx> > > > Reported-by: Matthew Rosato<mjrosato@xxxxxxxxxxxxxxxxxx> > > > --- > > > drivers/vhost/net.c | 23 +++++++++++++---------- > > > 1 file changed, 13 insertions(+), 10 deletions(-) > > > > > > v2: > > > - add Matthew as the reporter, thanks matthew. > > > - moving zero headcount check ahead instead of defer consuming skb > > > due to jason and mst's comment. > > > - add freeing skb in favor of recvmsg() fails. > > > > > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > > > index 8d626d7..e302e08 100644 > > > --- a/drivers/vhost/net.c > > > +++ b/drivers/vhost/net.c > > > @@ -778,16 +778,6 @@ static void handle_rx(struct vhost_net *net) > > > /* On error, stop handling until the next kick. */ > > > if (unlikely(headcount < 0)) > > > goto out; > > > - if (nvq->rx_array) > > > - msg.msg_control = vhost_net_buf_consume(&nvq->rxq); > > > - /* On overrun, truncate and discard */ > > > - if (unlikely(headcount > UIO_MAXIOV)) { > > > - iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1); > > > - err = sock->ops->recvmsg(sock, &msg, > > > - 1, MSG_DONTWAIT | MSG_TRUNC); > > > - pr_debug("Discarded rx packet: len %zd\n", sock_len); > > > - continue; > > > - } > > > /* OK, now we need to know about added descriptors. */ > > > if (!headcount) { > > > if (unlikely(vhost_enable_notify(&net->dev, vq))) { > > > @@ -800,6 +790,18 @@ static void handle_rx(struct vhost_net *net) > > > * they refilled. */ > > > goto out; > > > } > > > + if (nvq->rx_array) > > > + msg.msg_control = vhost_net_buf_consume(&nvq->rxq); > > > + /* On overrun, truncate and discard */ > > > + if (unlikely(headcount > UIO_MAXIOV)) { > > > + iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1); > > > + err = sock->ops->recvmsg(sock, &msg, > > > + 1, MSG_DONTWAIT | MSG_TRUNC); > > > + if (unlikely(err != 1)) > > Why 1? How is receiving 1 byte special or even possible? > > Also, I wouldn't put an unlikely here. It's all error handling code anyway. > > > > > + kfree_skb((struct sk_buff *)msg.msg_control); > > You do not need a cast here. > > Also, is it really safe to refer to msg_control here? > > I'd rather keep a copy of the skb pointer and use it than assume > > caller did not change it. But also see below. > > > > > + pr_debug("Discarded rx packet: len %zd\n", sock_len); > > > + continue; > > > + } > > > /* We don't need to be notified again. */ > > > iov_iter_init(&msg.msg_iter, READ, vq->iov, in, vhost_len); > > > fixup = msg.msg_iter; > > > @@ -818,6 +820,7 @@ static void handle_rx(struct vhost_net *net) > > > pr_debug("Discarded rx packet: " > > > " len %d, expected %zd\n", err, sock_len); > > > vhost_discard_vq_desc(vq, headcount); > > > + kfree_skb((struct sk_buff *)msg.msg_control); > > You do not need a cast here. > > > > Also, we have > > > > ret = tun_put_user(tun, tfile, skb, to); > > if (unlikely(ret < 0)) > > kfree_skb(skb); > > else > > consume_skb(skb); > > > > return ret; > > > > So it looks like recvmsg actually always consumes the skb. > > So I was wrong when I said you need to kfree it after > > recv msg, and your original patch was good. > > > > Jason, what do you think? > > > > tun_recvmsg() has the following check: > > static int tun_recvmsg(struct socket *sock, struct msghdr *m, size_t > total_len, > int flags) > { > struct tun_file *tfile = container_of(sock, struct tun_file, socket); > struct tun_struct *tun = __tun_get(tfile); > int ret; > > if (!tun) > return -EBADFD; > > if (flags & ~(MSG_DONTWAIT|MSG_TRUNC|MSG_ERRQUEUE)) { > ret = -EINVAL; > goto out; > } > > And tun_do_read() has: > > if (!iov_iter_count(to)) > return 0; > > So I think we need free skb in those cases. > > Thanks So it's a mess for callers. Let's free within tun then? -- MST _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
