Re: [PATCH net-next v5 3/5] netdevsim: forward skbs from one connected port to another
From: Jiri Pirko <jiri@resnulli.us>
Date: 2024-01-02 11:13:42
Thu, Dec 28, 2023 at 02:46:31AM CET, dw@davidwei.uk wrote:
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
I don't see the rtnl_lock take in those functions. Otherwise, this patch looks fine to me.
quoted hunk ↗ jump to hunk
concurrent calls to linking two netdevsims together. Signed-off-by: David Wei <redacted> --- drivers/net/netdevsim/netdev.c | 21 ++++++++++++++++++--- drivers/net/netdevsim/netdevsim.h | 1 + 2 files changed, 19 insertions(+), 3 deletions(-)diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c index 434322f6a565..0009d0f1243f 100644 --- a/drivers/net/netdevsim/netdev.c +++ b/drivers/net/netdevsim/netdev.c@@ -29,19 +29,34 @@static netdev_tx_t nsim_start_xmit(struct sk_buff *skb, struct net_device *dev) { struct netdevsim *ns = netdev_priv(dev); + struct netdevsim *peer_ns; + int ret = NETDEV_TX_OK; if (!nsim_ipsec_tx(ns, skb)) goto out; + rcu_read_lock(); + peer_ns = rcu_dereference(ns->peer); + if (!peer_ns) + goto out_stats; + + skb_tx_timestamp(skb); + if (unlikely(dev_forward_skb(peer_ns->netdev, skb) == NET_RX_DROP)) + ret = NET_XMIT_DROP; + +out_stats: + rcu_read_unlock(); u64_stats_update_begin(&ns->syncp); ns->tx_packets++; ns->tx_bytes += skb->len; + if (ret == NET_XMIT_DROP) + ns->tx_dropped++; u64_stats_update_end(&ns->syncp); + return ret; out: dev_kfree_skb(skb); - - return NETDEV_TX_OK; + return ret; } static void nsim_set_rx_mode(struct net_device *dev)@@ -70,6 +85,7 @@ 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 +318,6 @@ 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;diff --git a/drivers/net/netdevsim/netdevsim.h b/drivers/net/netdevsim/netdevsim.h index 24fc3fbda791..083b1ee7a1a2 100644 --- a/drivers/net/netdevsim/netdevsim.h +++ b/drivers/net/netdevsim/netdevsim.h@@ -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; -- 2.39.3