[PATCH net 1/2] tcp: call sk_data_ready() after listener migration

[Zhenzhong Wu <jt26wzz@gmail.com>]

When inet_csk_listen_stop() migrates an established child socket from
a closing listener to another socket in the same SO_REUSEPORT group,
the target listener gets a new accept-queue entry via
inet_csk_reqsk_queue_add(), but that path never notifies the target
listener's waiters.

As a result, a nonblocking accept() still succeeds because it checks
the accept queue directly, but waiters that sleep for listener
readiness can remain asleep until another connection generates a
wakeup. This affects poll()/epoll_wait()-based waiters, and can also
leave a blocking accept() asleep after migration even though the
child is already in the target listener's accept queue.

This was observed in a local test where listener A completed the
handshake, queued the child, and was closed before userspace called
accept(). The child was migrated to listener B, but listener B never
received a wakeup for the migrated accept-queue entry.

Call READ_ONCE(nsk->sk_data_ready)(nsk) after a successful migration
in inet_csk_listen_stop().

The reqsk_timer_handler() path does not need the same change:
half-open requests only become readable to userspace when the final
ACK completes the handshake, and tcp_child_process() already wakes
the listener in that case.

Fixes: 54b92e841937 ("tcp: Migrate TCP_ESTABLISHED/TCP_SYN_RECV sockets in accept queues.")
Cc: stable@vger.kernel.org
Signed-off-by: Zhenzhong Wu <jt26wzz@gmail.com>
---
 net/ipv4/inet_connection_sock.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 4ac3ae1bc..da1ce082f 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -1483,6 +1483,7 @@ void inet_csk_listen_stop(struct sock *sk)
 					__NET_INC_STATS(sock_net(nsk),
 							LINUX_MIB_TCPMIGRATEREQSUCCESS);
 					reqsk_migrate_reset(req);
+					READ_ONCE(nsk->sk_data_ready)(nsk);
 				} else {
 					__NET_INC_STATS(sock_net(nsk),
 							LINUX_MIB_TCPMIGRATEREQFAILURE);
-- 
2.43.0