[PATCH net v3 0/2] tcp: fix listener wakeup after reuseport migration

[Zhenzhong Wu <jt26wzz@gmail.com>]

This series fixes a missing wakeup when inet_csk_listen_stop() migrates
an established child socket from a closing listener to another socket
in the same SO_REUSEPORT group after the child has already been queued
for accept.

The target listener receives the migrated accept-queue entry via
inet_csk_reqsk_queue_add(), but its waiters are not notified.
Nonblocking accept() still succeeds because it checks the accept queue
directly, but readiness-based waiters can remain asleep until another
connection generates a wakeup.

Patch 1 notifies the target listener after a successful migration in
inet_csk_listen_stop() and protects the post-queue_add() nsk accesses
with rcu_read_lock()/rcu_read_unlock().

Patch 2 extends the existing migrate_reuseport BPF selftest with epoll
readiness checks inside migrate_dance(), around shutdown() where the
migration happens. The test now verifies that the target listener is
not ready before migration and becomes ready immediately after it, for
both TCP_ESTABLISHED and TCP_SYN_RECV. TCP_NEW_SYN_RECV remains
excluded because it still depends on later handshake completion.

Testing:
- On a local unpatched kernel, the focused migrate_reuseport test
  fails for the listener-migration cases and passes for the
  TCP_NEW_SYN_RECV cases:
    not ok 1 IPv4 TCP_ESTABLISHED  inet_csk_listen_stop
    not ok 2 IPv4 TCP_SYN_RECV     inet_csk_listen_stop
    ok 3 IPv4 TCP_NEW_SYN_RECV reqsk_timer_handler
    ok 4 IPv4 TCP_NEW_SYN_RECV inet_csk_complete_hashdance
    not ok 5 IPv6 TCP_ESTABLISHED  inet_csk_listen_stop
    not ok 6 IPv6 TCP_SYN_RECV     inet_csk_listen_stop
    ok 7 IPv6 TCP_NEW_SYN_RECV reqsk_timer_handler
    ok 8 IPv6 TCP_NEW_SYN_RECV inet_csk_complete_hashdance
- On a patched kernel booted under QEMU, the full migrate_reuseport
  selftest passes:
    ok 1 IPv4 TCP_ESTABLISHED  inet_csk_listen_stop
    ok 2 IPv4 TCP_SYN_RECV     inet_csk_listen_stop
    ok 3 IPv4 TCP_NEW_SYN_RECV reqsk_timer_handler
    ok 4 IPv4 TCP_NEW_SYN_RECV inet_csk_complete_hashdance
    ok 5 IPv6 TCP_ESTABLISHED  inet_csk_listen_stop
    ok 6 IPv6 TCP_SYN_RECV     inet_csk_listen_stop
    ok 7 IPv6 TCP_NEW_SYN_RECV reqsk_timer_handler
    ok 8 IPv6 TCP_NEW_SYN_RECV inet_csk_complete_hashdance
    SELFTEST_RC=0

---

v3:
- update the selftest patch as suggested by Kuniyuki Iwashima
- update the test flow comment to match the new epoll checks
- initialize epoll to -1 to avoid a compiler warning in the selftest

v2:
  https://lore.kernel.org/netdev/20260418181333.1713389-1-jt26wzz@gmail.com/

v1:
  https://lore.kernel.org/netdev/20260418041633.691435-1-jt26wzz@gmail.com/

Zhenzhong Wu (2):
  tcp: call sk_data_ready() after listener migration
  selftests/bpf: check epoll readiness during reuseport migration

 net/ipv4/inet_connection_sock.c               |  3 ++
 .../bpf/prog_tests/migrate_reuseport.c        | 46 ++++++++++++++++---
 2 files changed, 43 insertions(+), 6 deletions(-)


base-commit: 52bcb57a4e8a0865a76c587c2451906342ae1b2d
-- 
2.43.0