[PATCH net v4 2/2] inet: restore refcount ordering for lockless ehash walks
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HOTtoday
From: Hyunwoo Kim <hidden>
Date: 2026-10-26 00:38:45
Also in:
stable
Subsystem:
networking [general], networking [tcp], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Neal Cardwell, Linus Torvalds
Before commit fb041bb7c0a9 ("locking/refcount: Consolidate implementations
of refcount_t"), default builds implemented refcount_inc_not_zero() using
atomic_add_unless(), which provided full memory ordering on success. The
commit removed that ordering on weakly ordered architectures, allowing
validation after a successful reference acquisition in lockless ehash
walks to be reordered before it.
Use refcount_inc_not_zero_acquire() in the IPv4 and IPv6 established
lookups and in inet_twsk_purge(), where the network namespace is validated
again after taking a reference. Use refcount_set_release() when setting
refcounts in the SYN cookie, TCP Fast Open, request migration, and
TIME_WAIT paths. Keep the existing TIME_WAIT smp_wmb(), which separately
orders the refcount store before ehash publication.
Fixes: fb041bb7c0a9 ("locking/refcount: Consolidate implementations of refcount_t")
Cc: <redacted>
Signed-off-by: Hyunwoo Kim <redacted>
---
net/ipv4/inet_connection_sock.c | 6 +++---
net/ipv4/inet_hashtables.c | 2 +-
net/ipv4/inet_timewait_sock.c | 4 ++--
net/ipv4/syncookies.c | 2 +-
net/ipv4/tcp_fastopen.c | 2 +-
net/ipv6/inet6_hashtables.c | 2 +-
6 files changed, 9 insertions(+), 9 deletions(-)
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index bd0bad96c93c3..837cb91e5b173 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c@@ -1056,8 +1056,8 @@ static void reqsk_timer_handler(struct timer_list *t) * hold another count to prevent use-after-free and * call reqsk_put() just before return. */ - refcount_set(&nreq->rsk_refcnt, 2 + 1); timer_setup(&nreq->rsk_timer, reqsk_timer_handler, TIMER_PINNED); + refcount_set_release(&nreq->rsk_refcnt, 2 + 1); reqsk_queue_migrated(&inet_csk(nsk)->icsk_accept_queue, req); req = nreq;
@@ -1441,7 +1441,7 @@ struct sock *inet_csk_complete_hashdance(struct sock *sk, struct sock *child, goto child_put; } - refcount_set(&nreq->rsk_refcnt, 1); + refcount_set_release(&nreq->rsk_refcnt, 1); if (inet_csk_reqsk_queue_add(sk, nreq, child)) { __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQSUCCESS); reqsk_migrate_reset(req);
@@ -1494,7 +1494,7 @@ void inet_csk_listen_stop(struct sock *sk) if (nsk) { nreq = inet_reqsk_clone(req, nsk); if (nreq) { - refcount_set(&nreq->rsk_refcnt, 1); + refcount_set_release(&nreq->rsk_refcnt, 1); rcu_read_lock(); if (inet_csk_reqsk_queue_add(nsk, nreq, child)) {
diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index 58d54965036a2..7ffa9171d6de1 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c@@ -550,7 +550,7 @@ struct sock *__inet_lookup_established(const struct net *net, if (sk->sk_hash != hash) continue; if (likely(inet_match(net, sk, acookie, ports, dif, sdif))) { - if (unlikely(!refcount_inc_not_zero(&sk->sk_refcnt))) + if (unlikely(!refcount_inc_not_zero_acquire(&sk->sk_refcnt))) goto out; if (unlikely(hlist_nulls_unhashed_lockless(&sk->sk_nulls_node) || !inet_match(net, sk, acookie, ports, dif,
diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c
index d4c781a0667fe..74ff40d42e56b 100644
--- a/net/ipv4/inet_timewait_sock.c
+++ b/net/ipv4/inet_timewait_sock.c@@ -141,7 +141,7 @@ void inet_twsk_hashdance_schedule(struct inet_timewait_sock *tw, * Also note that after this point, we lost our implicit reference * so we are not allowed to use tw anymore. */ - refcount_set(&tw->tw_refcnt, 3); + refcount_set_release(&tw->tw_refcnt, 3); /* Ensure tw_refcnt has been set before tw is published. * smp_wmb() provides the necessary memory barrier to enforce this
@@ -328,7 +328,7 @@ void inet_twsk_purge(struct inet_hashinfo *hashinfo) if (check_net(sock_net(sk))) continue; - if (unlikely(!refcount_inc_not_zero(&sk->sk_refcnt))) + if (unlikely(!refcount_inc_not_zero_acquire(&sk->sk_refcnt))) continue; if (check_net(sock_net(sk))) {
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 6440305615378..4b2d2713653b7 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c@@ -205,7 +205,7 @@ struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb, child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst, NULL, &own_req, NULL); if (child) { - refcount_set(&req->rsk_refcnt, 1); + refcount_set_release(&req->rsk_refcnt, 1); sock_rps_save_rxhash(child, skb); if (rsk_drop_req(req)) {
diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index 471c78be55137..e40477b6b5549 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c@@ -364,7 +364,7 @@ static struct sock *tcp_fastopen_create_child(struct sock *sk, tcp_reset_xmit_timer(child, ICSK_TIME_RETRANS, req->timeout, false); - refcount_set(&req->rsk_refcnt, 2); + refcount_set_release(&req->rsk_refcnt, 2); sk_mark_napi_id_set(child, skb);
diff --git a/net/ipv6/inet6_hashtables.c b/net/ipv6/inet6_hashtables.c
index aa5fa1dd062f7..1eea584d80df8 100644
--- a/net/ipv6/inet6_hashtables.c
+++ b/net/ipv6/inet6_hashtables.c@@ -105,7 +105,7 @@ struct sock *__inet6_lookup_established(const struct net *net, continue; if (!inet6_match(net, sk, saddr, daddr, ports, dif, sdif)) continue; - if (unlikely(!refcount_inc_not_zero(&sk->sk_refcnt))) + if (unlikely(!refcount_inc_not_zero_acquire(&sk->sk_refcnt))) goto out; if (unlikely(hlist_nulls_unhashed_lockless(&sk->sk_nulls_node) ||
--
2.43.0