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

Tamir Duberstein
2026-04-22T03:04:36Z

On Tue, Apr 21, 2026 at 7:46 PM Zhenzhong Wu <jt26wzz@gmail.com> wrote:
>
> 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;
> + }

I think you can avoid this goto using `__attribute__((cleanup(...))`:

static void close_fd(int *fd)
{
if (*fd >= 0)
close(*fd);
}

#define __close_fd __attribute__((cleanup(close_fd)))

then in the test:

__close_fd int epoll = -1;

there's an example of this in
tools/testing/selftests/bpf/prog_tests/socket_helpers.h.