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

[Zhenzhong Wu]

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@xxxxxxxxxx> wrote:
>
> On Tue, Apr 21, 2026 at 7:46 PM Zhenzhong Wu <jt26wzz@xxxxxxxxx> 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@xxxxxxxxxx>
> > Reviewed-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
> > Signed-off-by: Zhenzhong Wu <jt26wzz@xxxxxxxxx>
> > ---
> >  .../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@xxxxxxxxxxxx>
> >   */
> >
> >  #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.