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netdevsim: forward skbs from one connected port to another 

Forward skbs sent from one netdevsim port to its connected netdevsim
port using dev_forward_skb, in a spirit similar to veth.

Add a tx_dropped variable to struct netdevsim, tracking the number of
skbs that could not be forwarded using dev_forward_skb().

The xmit() function accessing the peer ptr is protected by an RCU read
critical section. The rcu_read_lock() is functionally redundant as since
v5.0 all softirqs are implicitly RCU read critical sections; but it is
useful for human readers.

If another CPU is concurrently in nsim_destroy(), then it will first set
the peer ptr to NULL. This does not affect any existing readers that
dereferenced a non-NULL peer. Then, in unregister_netdevice(), there is
a synchronize_rcu() before the netdev is actually unregistered and
freed. This ensures that any readers i.e. xmit() that got a non-NULL
peer will complete before the netdev is freed.

Any readers after the RCU_INIT_POINTER() but before synchronize_rcu()
will dereference NULL, making it safe.

The codepath to nsim_destroy() and nsim_create() takes both the newly
added nsim_dev_list_lock and rtnl_lock. This makes it safe with
concurrent calls to linking two netdevsims together.

Signed-off-by: David Wei <dw@davidwei.uk>
Reviewed-by: Maciek Machnikowski <maciek@machnikowski.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David Wei 2024-02-28 15:22:50 -08:00 committed by David S. Miller
parent f532957d76
commit 9eb95228a7
2 changed files with 23 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
drivers/net/netdevsim/netdev.c
View File

@ -29,18 +29,35 @@
static netdev_tx_t nsim_start_xmit(struct sk_buff *skb, struct net_device *dev)
{
struct netdevsim *ns = netdev_priv(dev);
unsigned int len = skb->len;
struct netdevsim *peer_ns;
rcu_read_lock();
if (!nsim_ipsec_tx(ns, skb))
goto out;
goto out_drop_free;
peer_ns = rcu_dereference(ns->peer);
if (!peer_ns)
goto out_drop_free;
skb_tx_timestamp(skb);
if (unlikely(dev_forward_skb(peer_ns->netdev, skb) == NET_RX_DROP))
goto out_drop_cnt;
rcu_read_unlock();
u64_stats_update_begin(&ns->syncp);
ns->tx_packets++;
ns->tx_bytes += skb->len;
ns->tx_bytes += len;
u64_stats_update_end(&ns->syncp);
return NETDEV_TX_OK;
out:
out_drop_free:
dev_kfree_skb(skb);
out_drop_cnt:
rcu_read_unlock();
u64_stats_update_begin(&ns->syncp);
ns->tx_dropped++;
u64_stats_update_end(&ns->syncp);
return NETDEV_TX_OK;
}
@ -70,6 +87,7 @@ nsim_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats)
start = u64_stats_fetch_begin(&ns->syncp);
stats->tx_bytes = ns->tx_bytes;
stats->tx_packets = ns->tx_packets;
stats->tx_dropped = ns->tx_dropped;
} while (u64_stats_fetch_retry(&ns->syncp, start));
}
@ -302,7 +320,6 @@ static void nsim_setup(struct net_device *dev)
eth_hw_addr_random(dev);
dev->tx_queue_len = 0;
dev->flags |= IFF_NOARP;
dev->flags &= ~IFF_MULTICAST;
dev->priv_flags |= IFF_LIVE_ADDR_CHANGE |
IFF_NO_QUEUE;

1
drivers/net/netdevsim/netdevsim.h
View File

@ -98,6 +98,7 @@ struct netdevsim {
u64 tx_packets;
u64 tx_bytes;
u64 tx_dropped;
struct u64_stats_sync syncp;
struct nsim_bus_dev *nsim_bus_dev;