I encountered this issue in the middle of backporting scx, which
no longer exists since
a8532fac7b5d sched_ext: TASK_DEAD tasks must be switched into SCX
on ops_enable
61eeb9a90522 sched_ext: TASK_DEAD tasks must be switched out of
SCX on ops_disable
cuz TASK_DEAD tasks also go through scx init/exit path.
Thanks for your attention anyway:D
Regards,
Ze
On Mon, Feb 10, 2025 at 2:02 PM Ze Gao <zegao2021@xxxxxxxxx> wrote:
>
> Tests run in VM might be slow, so that children may exit before bpf
> programs are loaded. SCX_GE(skel->bss->init_task_cnt, num_pre_forks)
> would fail in this case.
>
> For tests working in any env, use signals to control the lifetime of
> children beyond bpf prog loading deterministically to get expected
> results.
>
> Signed-off-by: Ze Gao <zegao@xxxxxxxxxxx>
> ---
> .../selftests/sched_ext/init_enable_count.c | 27 ++++++++++++++++++-
> 1 file changed, 26 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/sched_ext/init_enable_count.c b/tools/testing/selftests/sched_ext/init_enable_count.c
> index 97d45f1e5597..3b2c8ab8464f 100644
> --- a/tools/testing/selftests/sched_ext/init_enable_count.c
> +++ b/tools/testing/selftests/sched_ext/init_enable_count.c
> @@ -31,6 +31,11 @@ open_load_prog(bool global)
> return skel;
> }
>
> +/* Signal handler for children */
> +void sigusr1_handler(int sig)
> +{
> +}
> +
> static enum scx_test_status run_test(bool global)
> {
> struct init_enable_count *skel;
> @@ -39,9 +44,15 @@ static enum scx_test_status run_test(bool global)
> int ret, i, status;
> struct sched_param param = {};
> pid_t pids[num_pre_forks];
> + sigset_t blocked_set;
>
> skel = open_load_prog(global);
>
> + /* Block SIGUSR1 in parent, children will inherit this*/
> + sigemptyset(&blocked_set);
> + sigaddset(&blocked_set, SIGUSR1);
> + sigprocmask(SIG_BLOCK, &blocked_set, NULL);
> +
> /*
> * Fork a bunch of children before we attach the scheduler so that we
> * ensure (at least in practical terms) that there are more tasks that
> @@ -52,7 +63,13 @@ static enum scx_test_status run_test(bool global)
> pids[i] = fork();
> SCX_FAIL_IF(pids[i] < 0, "Failed to fork child");
> if (pids[i] == 0) {
> - sleep(1);
> + signal(SIGUSR1, sigusr1_handler);
> + sigprocmask(SIG_UNBLOCK, &blocked_set, NULL);
> + /*
> + * Wait indefinitely for signal, will be interrupted
> + * by signal handler.
> + */
> + pause();
> exit(0);
> }
> }
> @@ -60,6 +77,13 @@ static enum scx_test_status run_test(bool global)
> link = bpf_map__attach_struct_ops(skel->maps.init_enable_count_ops);
> SCX_FAIL_IF(!link, "Failed to attach struct_ops");
>
> + /* Give children time to set up handlers */
> + sleep(1);
> +
> + /* Send SIGUSR1 to all children */
> + for (int i = 0; i < num_pre_forks; i++)
> + kill(pids[i], SIGUSR1);
> +
> for (i = 0; i < num_pre_forks; i++) {
> SCX_FAIL_IF(waitpid(pids[i], &status, 0) != pids[i],
> "Failed to wait for pre-forked child\n");
> @@ -69,6 +93,7 @@ static enum scx_test_status run_test(bool global)
> }
>
> bpf_link__destroy(link);
> + SCX_EQ(skel->bss->init_task_cnt, skel->bss->exit_task_cnt);
> SCX_GE(skel->bss->init_task_cnt, num_pre_forks);
> SCX_GE(skel->bss->exit_task_cnt, num_pre_forks);
>
> --
> 2.41.1
>
