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

Zhenzhong Wu
2026-04-22T06:34:39Z

Thanks Tamir, I will fold this into v5 - there's already a precedent
in socket_helpers.h, so I will just include it from there.

On Wed, Apr 22, 2026 at 11:04 AM Tamir Duberstein <tamird@kernel.org> wrote:
>
> 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.