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Date: Tue, 14 Jan 2014 16:45:24 +0800
From: Jason Wang <jasowang@...hat.com>
To: "Michael S. Tsirkin" <mst@...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 01/14/2014 04:25 PM, Michael S. Tsirkin wrote:
> 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.
But it looks like a buggy API, since tx_queue_len should be for qdisc
queue length instead of device itself. If we really want to preserve the
behaviour, how about using a new feature flag and change the behaviour
only when the device is created (TUNSETIFF) with the new flag?
>
> 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.
If I read the patch correctly, it will make no way for the user who
really want to change the qdisc queue length for tun.
>
>
>> ---
>> 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?
>
Ok, we can change it back to 500 * 65535, but I'm not sure whether this
or not this value (about 32M) is too big for a single socket.
>> @@ -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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