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SubjectRe: [RFC 2/2] netvsc: use RCU for VF net device reference
Date
Stephen Hemminger <stephen@networkplumber.org> writes:

> Rather than keeping a pointer, a flag, and reference count, use RCU and existing
> device reference count to protect the synthetic to VF relationship.

Thanks! I like the idea. Some nitpicks below ...

>
> One other change is that injected packets must be accounted for on the synthetic
> device otherwise the statistics will be lost. The VF device driver (for most devices)
> creates the statistics based on device registers and therefore would ignore any direct
> manipulation of network device stats.
>
> Also, rx_dropped is not atomic_long.
>
> Signed-off-by: Stephen Hemminger <sthemmin@linuxonhyperv.com>
>
> --- a/drivers/net/hyperv/hyperv_net.h 2016-08-13 11:25:59.764085593 -0700
> +++ b/drivers/net/hyperv/hyperv_net.h 2016-08-13 11:25:59.736085464 -0700
> @@ -689,6 +689,9 @@ struct netvsc_device {
> wait_queue_head_t wait_drain;
> bool destroy;
>
> + /* State to manage the associated VF interface. */
> + struct net_device *vf_netdev __rcu;
> +
> /* Receive buffer allocated by us but manages by NetVSP */
> void *recv_buf;
> u32 recv_buf_size;
> @@ -739,10 +742,6 @@ struct netvsc_device {
> /* Serial number of the VF to team with */
> u32 vf_serial;
> atomic_t open_cnt;
> - /* State to manage the associated VF interface. */
> - bool vf_inject;
> - struct net_device *vf_netdev;
> - atomic_t vf_use_cnt;
> };
>
> static inline struct netvsc_device *
> --- a/drivers/net/hyperv/netvsc.c 2016-08-13 11:25:59.764085593 -0700
> +++ b/drivers/net/hyperv/netvsc.c 2016-08-13 11:25:59.736085464 -0700
> @@ -77,13 +77,10 @@ static struct netvsc_device *alloc_net_d
> init_waitqueue_head(&net_device->wait_drain);
> net_device->destroy = false;
> atomic_set(&net_device->open_cnt, 0);
> - atomic_set(&net_device->vf_use_cnt, 0);
> +
> net_device->max_pkt = RNDIS_MAX_PKT_DEFAULT;
> net_device->pkt_align = RNDIS_PKT_ALIGN_DEFAULT;
>
> - net_device->vf_netdev = NULL;
> - net_device->vf_inject = false;
> -
> return net_device;
> }
>
> --- a/drivers/net/hyperv/netvsc_drv.c 2016-08-13 11:25:59.764085593 -0700
> +++ b/drivers/net/hyperv/netvsc_drv.c 2016-08-13 11:31:47.733685146 -0700
> @@ -668,59 +668,45 @@ int netvsc_recv_callback(struct hv_devic
> {
> struct net_device *net = hv_get_drvdata(device_obj);
> struct net_device_context *net_device_ctx = netdev_priv(net);
> - struct sk_buff *skb;
> - struct sk_buff *vf_skb;
> - struct netvsc_stats *rx_stats;
> + struct netvsc_stats *rx_stats = this_cpu_ptr(net_device_ctx->rx_stats);
> struct netvsc_device *netvsc_dev = net_device_ctx->nvdev;
> - u32 bytes_recvd = packet->total_data_buflen;
> - int ret = 0;
> + struct net_device *vf_netdev;
> + struct sk_buff *skb;
>
> if (!net || net->reg_state != NETREG_REGISTERED)
> return NVSP_STAT_FAIL;
>
> - if (READ_ONCE(netvsc_dev->vf_inject)) {
> - atomic_inc(&netvsc_dev->vf_use_cnt);
> - if (!READ_ONCE(netvsc_dev->vf_inject)) {
> - /*
> - * We raced; just move on.
> - */
> - atomic_dec(&netvsc_dev->vf_use_cnt);
> - goto vf_injection_done;
> - }
> + vf_netdev = rcu_dereference(netvsc_dev->vf_netdev);
> + if (vf_netdev) {
> + /* Inject this packet into the VF interface. On
> + * Hyper-V, multicast and broadcast packets are only
> + * delivered on the synthetic interface (after
> + * subjecting these to policy filters on the
> + * host). Deliver these via the VF interface in the
> + * guest if up, otherwise drop.
> + */
> + if (!netif_running(vf_netdev))
> + goto drop;

Why drop? In case VF is not running I guess it would be better to
receive the packet through netvsc interface.

>
> - /*
> - * Inject this packet into the VF inerface.
> - * On Hyper-V, multicast and brodcast packets
> - * are only delivered on the synthetic interface
> - * (after subjecting these to policy filters on
> - * the host). Deliver these via the VF interface
> - * in the guest.
> + /* Account for this on the synthetic interface
> + * otherwise likely to be not accounted for since
> + * device statistics on the VF are driver dependent.
> */
> - vf_skb = netvsc_alloc_recv_skb(netvsc_dev->vf_netdev, packet,
> - csum_info, *data, vlan_tci);
> - if (vf_skb != NULL) {
> - ++netvsc_dev->vf_netdev->stats.rx_packets;
> - netvsc_dev->vf_netdev->stats.rx_bytes += bytes_recvd;
> - netif_receive_skb(vf_skb);
> - } else {
> - ++net->stats.rx_dropped;
> - ret = NVSP_STAT_FAIL;
> - }
> - atomic_dec(&netvsc_dev->vf_use_cnt);
> - return ret;
> + ++net->stats.multicast;

And if the packet is broadcast and not multicast?

> + net = vf_netdev;
> }
>
> -vf_injection_done:
> - rx_stats = this_cpu_ptr(net_device_ctx->rx_stats);
> -
> /* Allocate a skb - TODO direct I/O to pages? */
> skb = netvsc_alloc_recv_skb(net, packet, csum_info, *data, vlan_tci);
> if (unlikely(!skb)) {
> +drop:
> ++net->stats.rx_dropped;
> return NVSP_STAT_FAIL;
> }
> - skb_record_rx_queue(skb, channel->
> - offermsg.offer.sub_channel_index);
> +
> + if (likely(!vf_netdev))
> + skb_record_rx_queue(skb,
> + channel->offermsg.offer.sub_channel_index);
>
> u64_stats_update_begin(&rx_stats->syncp);
> rx_stats->packets++;
> @@ -989,6 +975,7 @@ static struct rtnl_link_stats64 *netvsc_
>
> t->rx_dropped = net->stats.rx_dropped;
> t->rx_errors = net->stats.rx_errors;
> + t->multicast = net->stats.multicast;
>
> return t;
> }
> @@ -1170,8 +1157,7 @@ static void netvsc_notify_peers(struct w
> gwrk = container_of(wrk, struct garp_wrk, dwrk);
>
> netdev_notify_peers(gwrk->netdev);
> -
> - atomic_dec(&gwrk->netvsc_dev->vf_use_cnt);
> + dev_put(gwrk->netdev);
> }
>
> static struct net_device *get_netvsc_net_device(char *mac)
> @@ -1222,7 +1208,7 @@ static int netvsc_register_vf(struct net
> netdev_info(ndev, "VF registering: %s\n", vf_netdev->name);
>
> dev_hold(vf_netdev);
> - netvsc_dev->vf_netdev = vf_netdev;
> + rcu_assign_pointer(netvsc_dev->vf_netdev, vf_netdev);
> return NOTIFY_OK;
> }
>
> @@ -1248,7 +1234,6 @@ static int netvsc_vf_up(struct net_devic
> return NOTIFY_DONE;
>
> netdev_info(ndev, "VF up: %s\n", vf_netdev->name);
> - netvsc_dev->vf_inject = true;
>
> /*
> * Open the device before switching data path.
> @@ -1268,7 +1253,7 @@ static int netvsc_vf_up(struct net_devic
> * notify peers; take a reference to prevent
> * the VF interface from vanishing.
> */
> - atomic_inc(&netvsc_dev->vf_use_cnt);
> + dev_hold(vf_netdev);

PATCH net 4/4 of my series drops gwrk.dwrk completely so depending on
the patch order this may not be needed...

> net_device_ctx->gwrk.netdev = vf_netdev;
> net_device_ctx->gwrk.netvsc_dev = netvsc_dev;
> schedule_work(&net_device_ctx->gwrk.dwrk);
> @@ -1298,14 +1283,7 @@ static int netvsc_vf_down(struct net_dev
> return NOTIFY_DONE;
>
> netdev_info(ndev, "VF down: %s\n", vf_netdev->name);
> - netvsc_dev->vf_inject = false;
> - /*
> - * Wait for currently active users to
> - * drain out.
> - */
>
> - while (atomic_read(&netvsc_dev->vf_use_cnt) != 0)
> - udelay(50);
> netvsc_switch_datapath(ndev, false);
> netdev_info(ndev, "Data path switched from VF: %s\n", vf_netdev->name);
> rndis_filter_close(netvsc_dev);
> @@ -1313,7 +1291,7 @@ static int netvsc_vf_down(struct net_dev
> /*
> * Notify peers.
> */
> - atomic_inc(&netvsc_dev->vf_use_cnt);
> + dev_hold(ndev);
> net_device_ctx->gwrk.netdev = ndev;
> net_device_ctx->gwrk.netvsc_dev = netvsc_dev;
> schedule_work(&net_device_ctx->gwrk.dwrk);
> @@ -1342,7 +1320,7 @@ static int netvsc_unregister_vf(struct n
> return NOTIFY_DONE;
> netdev_info(ndev, "VF unregistering: %s\n", vf_netdev->name);
>
> - netvsc_dev->vf_netdev = NULL;
> + RCU_INIT_POINTER(netvsc_dev->vf_netdev, NULL);
> dev_put(vf_netdev);
> return NOTIFY_OK;
> }

I'd also suggest you split your patch into two - switch to using RCU and
stats changes as these changes are more or less independent.

--
Vitaly

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