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Date: Tue, 14 Jan 2014 10:25:16 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, Vlad Yasevich <vyasevic@...hat.com>,
John Fastabend <john.r.fastabend@...el.com>,
Stephen Hemminger <stephen@...workplumber.org>,
Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [PATCH net-next] tun/macvtap: limit the packets queued through
rcvbuf
On Tue, Jan 14, 2014 at 02:53:07PM +0800, Jason Wang wrote:
> We used to limit the number of packets queued through tx_queue_length. This
> has several issues:
>
> - tx_queue_length is the control of qdisc queue length, simply reusing it
> to control the packets queued by device may cause confusion.
> - After commit 6acf54f1cf0a6747bac9fea26f34cfc5a9029523 ("macvtap: Add
> support of packet capture on macvtap device."), an unexpected qdisc
> caused by non-zero tx_queue_length will lead qdisc lock contention for
> multiqueue deivce.
> - What we really want is to limit the total amount of memory occupied not
> the number of packets.
>
> So this patch tries to solve the above issues by using socket rcvbuf to
> limit the packets could be queued for tun/macvtap. This was done by using
> sock_queue_rcv_skb() instead of a direct call to skb_queue_tail(). Also two
> new ioctl() were introduced for userspace to change the rcvbuf like what we
> have done for sndbuf.
>
> With this fix, we can safely change the tx_queue_len of macvtap to
> zero. This will make multiqueue works without extra lock contention.
>
> Cc: Vlad Yasevich <vyasevic@...hat.com>
> Cc: Michael S. Tsirkin <mst@...hat.com>
> Cc: John Fastabend <john.r.fastabend@...el.com>
> Cc: Stephen Hemminger <stephen@...workplumber.org>
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
No, I don't think we can change userspace-visible behaviour like that.
This will break any existing user that tries to control
queue length through sysfs,netlink or device ioctl.
Take a look at my patch in msg ID 20140109071721.GD19559@...hat.com
which gives one way to set tx_queue_len to zero without
breaking userspace.
> ---
> drivers/net/macvtap.c | 31 ++++++++++++++++++++---------
> drivers/net/tun.c | 48 +++++++++++++++++++++++++++++++++------------
> include/uapi/linux/if_tun.h | 3 +++
> 3 files changed, 60 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index a2c3a89..c429c56 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -292,9 +292,6 @@ static rx_handler_result_t macvtap_handle_frame(struct sk_buff **pskb)
> if (!q)
> return RX_HANDLER_PASS;
>
> - if (skb_queue_len(&q->sk.sk_receive_queue) >= dev->tx_queue_len)
> - goto drop;
> -
> skb_push(skb, ETH_HLEN);
>
> /* Apply the forward feature mask so that we perform segmentation
> @@ -310,8 +307,10 @@ static rx_handler_result_t macvtap_handle_frame(struct sk_buff **pskb)
> goto drop;
>
> if (!segs) {
> - skb_queue_tail(&q->sk.sk_receive_queue, skb);
> - goto wake_up;
> + if (sock_queue_rcv_skb(&q->sk, skb))
> + goto drop;
> + else
> + goto wake_up;
> }
>
> kfree_skb(skb);
> @@ -319,11 +318,17 @@ static rx_handler_result_t macvtap_handle_frame(struct sk_buff **pskb)
> struct sk_buff *nskb = segs->next;
>
> segs->next = NULL;
> - skb_queue_tail(&q->sk.sk_receive_queue, segs);
> + if (sock_queue_rcv_skb(&q->sk, segs)) {
> + skb = segs;
> + skb->next = nskb;
> + goto drop;
> + }
> +
> segs = nskb;
> }
> } else {
> - skb_queue_tail(&q->sk.sk_receive_queue, skb);
> + if (sock_queue_rcv_skb(&q->sk, skb))
> + goto drop;
> }
>
> wake_up:
> @@ -333,7 +338,7 @@ wake_up:
> drop:
> /* Count errors/drops only here, thus don't care about args. */
> macvlan_count_rx(vlan, 0, 0, 0);
> - kfree_skb(skb);
> + kfree_skb_list(skb);
> return RX_HANDLER_CONSUMED;
> }
>
> @@ -414,7 +419,7 @@ static void macvtap_dellink(struct net_device *dev,
> static void macvtap_setup(struct net_device *dev)
> {
> macvlan_common_setup(dev);
> - dev->tx_queue_len = TUN_READQ_SIZE;
> + dev->tx_queue_len = 0;
> }
>
> static struct rtnl_link_ops macvtap_link_ops __read_mostly = {
> @@ -469,6 +474,7 @@ static int macvtap_open(struct inode *inode, struct file *file)
> sock_init_data(&q->sock, &q->sk);
> q->sk.sk_write_space = macvtap_sock_write_space;
> q->sk.sk_destruct = macvtap_sock_destruct;
> + q->sk.sk_rcvbuf = TUN_RCVBUF;
> q->flags = IFF_VNET_HDR | IFF_NO_PI | IFF_TAP;
> q->vnet_hdr_sz = sizeof(struct virtio_net_hdr);
>
> @@ -1040,6 +1046,13 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
> q->sk.sk_sndbuf = u;
> return 0;
>
> + case TUNSETRCVBUF:
> + if (get_user(u, up))
> + return -EFAULT;
> +
> + q->sk.sk_rcvbuf = u;
> + return 0;
> +
> case TUNGETVNETHDRSZ:
> s = q->vnet_hdr_sz;
> if (put_user(s, sp))
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 09f6662..7a08fa3 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -177,6 +177,7 @@ struct tun_struct {
>
> int vnet_hdr_sz;
> int sndbuf;
> + int rcvbuf;
> struct tap_filter txflt;
> struct sock_fprog fprog;
> /* protected by rtnl lock */
> @@ -771,17 +772,6 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
> if (!check_filter(&tun->txflt, skb))
> goto drop;
>
> - if (tfile->socket.sk->sk_filter &&
> - sk_filter(tfile->socket.sk, skb))
> - goto drop;
> -
> - /* Limit the number of packets queued by dividing txq length with the
> - * number of queues.
> - */
> - if (skb_queue_len(&tfile->socket.sk->sk_receive_queue)
> - >= dev->tx_queue_len / tun->numqueues)
> - goto drop;
> -
> if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC)))
> goto drop;
>
> @@ -798,7 +788,8 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
> nf_reset(skb);
>
> /* Enqueue packet */
> - skb_queue_tail(&tfile->socket.sk->sk_receive_queue, skb);
> + if (sock_queue_rcv_skb(tfile->socket.sk, skb))
> + goto drop;
>
> /* Notify and wake up reader process */
> if (tfile->flags & TUN_FASYNC)
> @@ -1668,6 +1659,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
>
> tun->filter_attached = false;
> tun->sndbuf = tfile->socket.sk->sk_sndbuf;
> + tun->rcvbuf = tfile->socket.sk->sk_rcvbuf;
>
> spin_lock_init(&tun->lock);
>
> @@ -1837,6 +1829,17 @@ static void tun_set_sndbuf(struct tun_struct *tun)
> }
> }
>
> +static void tun_set_rcvbuf(struct tun_struct *tun)
> +{
> + struct tun_file *tfile;
> + int i;
> +
> + for (i = 0; i < tun->numqueues; i++) {
> + tfile = rtnl_dereference(tun->tfiles[i]);
> + tfile->socket.sk->sk_sndbuf = tun->sndbuf;
> + }
> +}
> +
> static int tun_set_queue(struct file *file, struct ifreq *ifr)
> {
> struct tun_file *tfile = file->private_data;
> @@ -1878,7 +1881,7 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
> struct ifreq ifr;
> kuid_t owner;
> kgid_t group;
> - int sndbuf;
> + int sndbuf, rcvbuf;
> int vnet_hdr_sz;
> unsigned int ifindex;
> int ret;
> @@ -2061,6 +2064,22 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
> tun_set_sndbuf(tun);
> break;
>
> + case TUNGETRCVBUF:
> + rcvbuf = tfile->socket.sk->sk_rcvbuf;
> + if (copy_to_user(argp, &rcvbuf, sizeof(rcvbuf)))
> + ret = -EFAULT;
> + break;
> +
> + case TUNSETRCVBUF:
> + if (copy_from_user(&rcvbuf, argp, sizeof(rcvbuf))) {
> + ret = -EFAULT;
> + break;
> + }
> +
> + tun->rcvbuf = rcvbuf;
> + tun_set_rcvbuf(tun);
> + break;
> +
> case TUNGETVNETHDRSZ:
> vnet_hdr_sz = tun->vnet_hdr_sz;
> if (copy_to_user(argp, &vnet_hdr_sz, sizeof(vnet_hdr_sz)))
> @@ -2139,6 +2158,8 @@ static long tun_chr_compat_ioctl(struct file *file,
> case TUNSETTXFILTER:
> case TUNGETSNDBUF:
> case TUNSETSNDBUF:
> + case TUNGETRCVBUF:
> + case TUNSETRCVBUF:
> case SIOCGIFHWADDR:
> case SIOCSIFHWADDR:
> arg = (unsigned long)compat_ptr(arg);
> @@ -2204,6 +2225,7 @@ static int tun_chr_open(struct inode *inode, struct file * file)
>
> tfile->sk.sk_write_space = tun_sock_write_space;
> tfile->sk.sk_sndbuf = INT_MAX;
> + tfile->sk.sk_rcvbuf = TUN_RCVBUF;
>
> file->private_data = tfile;
> set_bit(SOCK_EXTERNALLY_ALLOCATED, &tfile->socket.flags);
> diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
> index e9502dd..8e04657 100644
> --- a/include/uapi/linux/if_tun.h
> +++ b/include/uapi/linux/if_tun.h
> @@ -22,6 +22,7 @@
>
> /* Read queue size */
> #define TUN_READQ_SIZE 500
> +#define TUN_RCVBUF (512 * PAGE_SIZE)
>
> /* TUN device flags */
> #define TUN_TUN_DEV 0x0001
That's about 16x less than we were able to queue previously
by default.
How can you be sure this won't break any applications?
> @@ -58,6 +59,8 @@
> #define TUNSETQUEUE _IOW('T', 217, int)
> #define TUNSETIFINDEX _IOW('T', 218, unsigned int)
> #define TUNGETFILTER _IOR('T', 219, struct sock_fprog)
> +#define TUNGETRCVBUF _IOR('T', 220, int)
> +#define TUNSETRCVBUF _IOW('T', 221, int)
>
> /* TUNSETIFF ifr flags */
> #define IFF_TUN 0x0001
> --
> 1.8.3.2
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