pppoe: drop sock reference counting on fast path

Now that PPPoE sockets are freed via RCU (SOCK_RCU_FREE), it is no longer
necessary to take a reference count when looking up sockets on the receive
path. Readers are protected by RCU, so the socket memory remains valid
until after a grace period.

Convert fast-path lookups to avoid refcounting:
 - Replace get_item() and sk_receive_skb() in pppoe_rcv() with
   __get_item() and __sk_receive_skb().
 - Rework get_item_by_addr() into __get_item_by_addr() (no refcount and
   move RCU lock into pppoe_ioctl)
 - Remove unnecessary sock_put() calls.

This avoids cacheline bouncing from atomic reference counting and improves
performance on the receive fast path.

Signed-off-by: Qingfang Deng <dqfext@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250828012018.15922-2-dqfext@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/ppp/pppoe.c b/drivers/net/ppp/pppoe.c
index 54522b26b728ca68d654fcc4592acaa0b0040b88..4ac6afce267b93e30d6e4e1930ed64f28bc48ba0 100644 (file)
--- a/drivers/net/ppp/pppoe.c
+++ b/drivers/net/ppp/pppoe.c
@@ -237,8 +237,8 @@ static inline struct pppox_sock *get_item(struct pppoe_net *pn, __be16 sid,
        return po;
 }
 
-static inline struct pppox_sock *get_item_by_addr(struct net *net,
-                                               struct sockaddr_pppox *sp)
+static inline struct pppox_sock *__get_item_by_addr(struct net *net,
+                                                   struct sockaddr_pppox *sp)
 {
        struct net_device *dev;
        struct pppoe_net *pn;
@@ -246,15 +246,13 @@ static inline struct pppox_sock *get_item_by_addr(struct net *net,
 
        int ifindex;
 
-       rcu_read_lock();
        dev = dev_get_by_name_rcu(net, sp->sa_addr.pppoe.dev);
        if (dev) {
                ifindex = dev->ifindex;
                pn = pppoe_pernet(net);
-               pppox_sock = get_item(pn, sp->sa_addr.pppoe.sid,
-                               sp->sa_addr.pppoe.remote, ifindex);
+               pppox_sock = __get_item(pn, sp->sa_addr.pppoe.sid,
+                                       sp->sa_addr.pppoe.remote, ifindex);
        }
-       rcu_read_unlock();
        return pppox_sock;
 }
 
@@ -381,18 +379,16 @@ static int pppoe_rcv_core(struct sock *sk, struct sk_buff *skb)
        if (sk->sk_state & PPPOX_BOUND) {
                ppp_input(&po->chan, skb);
        } else if (sk->sk_state & PPPOX_RELAY) {
-               relay_po = get_item_by_addr(sock_net(sk),
-                                           &po->pppoe_relay);
+               relay_po = __get_item_by_addr(sock_net(sk),
+                                             &po->pppoe_relay);
                if (relay_po == NULL)
                        goto abort_kfree;
 
                if ((sk_pppox(relay_po)->sk_state & PPPOX_CONNECTED) == 0)
-                       goto abort_put;
+                       goto abort_kfree;
 
                if (!__pppoe_xmit(sk_pppox(relay_po), skb))
-                       goto abort_put;
-
-               sock_put(sk_pppox(relay_po));
+                       goto abort_kfree;
        } else {
                if (sock_queue_rcv_skb(sk, skb))
                        goto abort_kfree;
@@ -400,9 +396,6 @@ static int pppoe_rcv_core(struct sock *sk, struct sk_buff *skb)
 
        return NET_RX_SUCCESS;
 
-abort_put:
-       sock_put(sk_pppox(relay_po));
-
 abort_kfree:
        kfree_skb(skb);
        return NET_RX_DROP;
@@ -447,14 +440,11 @@ static int pppoe_rcv(struct sk_buff *skb, struct net_device *dev,
        ph = pppoe_hdr(skb);
        pn = pppoe_pernet(dev_net(dev));
 
-       /* Note that get_item does a sock_hold(), so sk_pppox(po)
-        * is known to be safe.
-        */
-       po = get_item(pn, ph->sid, eth_hdr(skb)->h_source, dev->ifindex);
+       po = __get_item(pn, ph->sid, eth_hdr(skb)->h_source, dev->ifindex);
        if (!po)
                goto drop;
 
-       return sk_receive_skb(sk_pppox(po), skb, 0);
+       return __sk_receive_skb(sk_pppox(po), skb, 0, 1, false);
 
 drop:
        kfree_skb(skb);
@@ -820,11 +810,12 @@ static int pppoe_ioctl(struct socket *sock, unsigned int cmd,
 
                /* Check that the socket referenced by the address
                   actually exists. */
-               relay_po = get_item_by_addr(sock_net(sk), &po->pppoe_relay);
+               rcu_read_lock();
+               relay_po = __get_item_by_addr(sock_net(sk), &po->pppoe_relay);
+               rcu_read_unlock();
                if (!relay_po)
                        break;
 
-               sock_put(sk_pppox(relay_po));
                sk->sk_state |= PPPOX_RELAY;
                err = 0;
                break;