[PATCH v2 09/12] soreuseport: publish num_socks with acquire/release

[Jinjie Ruan <ruanjinjie@huawei.com>]

Replace the smp_wmb()/smp_rmb() barrier pair with
smp_store_release()/smp_load_acquire() on reuse->num_socks.
Writers publish socks[] updates via release before incrementing
or decrementing the count; readers acquire the count before
accessing socks[], ensuring they observe a consistent view.

The detach path gains proper ordering between the socks[] write and
the decrement, which was previously unordered.

No functional change intended.

Cc: Eric Dumazet <edumazet@google.com>
Cc: Kuniyuki Iwashima <kuniyu@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Simon Horman <horms@kernel.org>
Assisted-by: DeepSeek:DeepSeek-V3
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
---
 net/core/sock_reuseport.c | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/net/core/sock_reuseport.c b/net/core/sock_reuseport.c
index 29948cb44b7d..6d3c511d1def 100644
--- a/net/core/sock_reuseport.c
+++ b/net/core/sock_reuseport.c
@@ -125,9 +125,8 @@ static void __reuseport_add_sock(struct sock *sk,
 				 struct sock_reuseport *reuse)
 {
 	reuse->socks[reuse->num_socks] = sk;
-	/* paired with smp_rmb() in reuseport_(select|migrate)_sock() */
-	smp_wmb();
-	reuse->num_socks++;
+	/* paired with smp_load_acquire() in reuseport_(select|migrate)_sock() */
+	smp_store_release(&reuse->num_socks, reuse->num_socks + 1);
 	reuseport_get_incoming_cpu(sk, reuse);
 }
 
@@ -140,7 +139,8 @@ static bool __reuseport_detach_sock(struct sock *sk,
 		return false;
 
 	reuse->socks[i] = reuse->socks[reuse->num_socks - 1];
-	reuse->num_socks--;
+	/* paired with smp_load_acquire() in reuseport_(select|migrate)_sock() */
+	smp_store_release(&reuse->num_socks, reuse->num_socks - 1);
 	reuseport_put_incoming_cpu(sk, reuse);
 
 	return true;
@@ -583,11 +583,9 @@ struct sock *reuseport_select_sock(struct sock *sk,
 		goto out;
 
 	prog = rcu_dereference(reuse->prog);
-	socks = READ_ONCE(reuse->num_socks);
+	/* paired with smp_store_release() in __reuseport_add_sock() */
+	socks = smp_load_acquire(&reuse->num_socks);
 	if (likely(socks)) {
-		/* paired with smp_wmb() in __reuseport_add_sock() */
-		smp_rmb();
-
 		if (!prog || !skb)
 			goto select_by_hash;
 
@@ -634,13 +632,11 @@ struct sock *reuseport_migrate_sock(struct sock *sk,
 	if (!reuse)
 		goto out;
 
-	socks = READ_ONCE(reuse->num_socks);
+	/* paired with smp_store_release() in __reuseport_add_sock() */
+	socks = smp_load_acquire(&reuse->num_socks);
 	if (unlikely(!socks))
 		goto failure;
 
-	/* paired with smp_wmb() in __reuseport_add_sock() */
-	smp_rmb();
-
 	hash = migrating_sk->sk_hash;
 	prog = rcu_dereference(reuse->prog);
 	if (!prog || prog->expected_attach_type != BPF_SK_REUSEPORT_SELECT_OR_MIGRATE) {
-- 
2.34.1