[PATCH net v4 2/2] selftests/bpf: check epoll readiness during reuseport migration

Zhenzhong Wu
2026-04-22T02:46:41Z

Inside migrate_dance(), add epoll checks around shutdown() to
verify that the target listener is not ready before shutdown()
and becomes ready immediately after shutdown() triggers migration.

Cover TCP_ESTABLISHED and TCP_SYN_RECV. Exclude TCP_NEW_SYN_RECV
as it depends on later handshake completion.

Suggested-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Signed-off-by: Zhenzhong Wu <jt26wzz@gmail.com>
---
.../bpf/prog_tests/migrate_reuseport.c | 49 ++++++++++++++++---
1 file changed, 42 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/migrate_reuseport.c b/tools/testing/selftests/bpf/prog_tests/migrate_reuseport.c
index 653b0a20f..c62907732 100644
--- a/tools/testing/selftests/bpf/prog_tests/migrate_reuseport.c
+++ b/tools/testing/selftests/bpf/prog_tests/migrate_reuseport.c
@@ -7,24 +7,29 @@
* 3. call listen() for 1 server socket. (migration target)
* 4. update a map to migrate all child sockets
* to the last server socket (migrate_map[cookie] = 4)
- * 5. call shutdown() for first 4 server sockets
+ * 5. for TCP_ESTABLISHED and TCP_SYN_RECV cases, verify via epoll
+ * that the last server socket is not ready before migration.
+ * 6. call shutdown() for first 4 server sockets
* and migrate the requests in the accept queue
* to the last server socket.
- * 6. call listen() for the second server socket.
- * 7. call shutdown() for the last server
+ * 7. for TCP_ESTABLISHED and TCP_SYN_RECV cases, verify via epoll
+ * that the last server socket is ready after migration.
+ * 8. call listen() for the second server socket.
+ * 9. call shutdown() for the last server
* and migrate the requests in the accept queue
* to the second server socket.
- * 8. call listen() for the last server.
- * 9. call shutdown() for the second server
+ * 10. call listen() for the last server.
+ * 11. call shutdown() for the second server
* and migrate the requests in the accept queue
* to the last server socket.
- * 10. call accept() for the last server socket.
+ * 12. call accept() for the last server socket.
*
* Author: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
*/

#include <bpf/bpf.h>
#include <bpf/libbpf.h>
+#include <sys/epoll.h>

#include "test_progs.h"
#include "test_migrate_reuseport.skel.h"
@@ -350,21 +355,51 @@ static int update_maps(struct migrate_reuseport_test_case *test_case,

static int migrate_dance(struct migrate_reuseport_test_case *test_case)
{
+ struct epoll_event ev = {
+ .events = EPOLLIN,
+ };
+ int epoll = -1, nfds;
int i, err;

+ if (test_case->state != BPF_TCP_NEW_SYN_RECV) {
+ epoll = epoll_create1(0);
+ if (!ASSERT_NEQ(epoll, -1, "epoll_create1"))
+ return -1;
+
+ ev.data.fd = test_case->servers[MIGRATED_TO];
+ if (!ASSERT_OK(epoll_ctl(epoll, EPOLL_CTL_ADD,
+ test_case->servers[MIGRATED_TO], &ev),
+ "epoll_ctl"))
+ goto close_epoll;
+
+ nfds = epoll_wait(epoll, &ev, 1, 0);
+ if (!ASSERT_EQ(nfds, 0, "epoll_wait 1"))
+ goto close_epoll;
+ }
+
/* Migrate TCP_ESTABLISHED and TCP_SYN_RECV requests
* to the last listener based on eBPF.
*/
for (i = 0; i < MIGRATED_TO; i++) {
err = shutdown(test_case->servers[i], SHUT_RDWR);
if (!ASSERT_OK(err, "shutdown"))
- return -1;
+ goto close_epoll;
}

/* No dance for TCP_NEW_SYN_RECV to migrate based on eBPF */
if (test_case->state == BPF_TCP_NEW_SYN_RECV)
return 0;

+ nfds = epoll_wait(epoll, &ev, 1, 0);
+ if (!ASSERT_EQ(nfds, 1, "epoll_wait 2")) {
+close_epoll:
+ if (epoll >= 0)
+ close(epoll);
+ return -1;
+ }
+
+ close(epoll);
+
/* Note that we use the second listener instead of the
* first one here.
*
--
2.43.0