[PATCH bpf-next] selftests/bpf: Drop the on_enter recursion check of task_local_storage

[PATCH bpf-next] selftests/bpf: Drop the on_enter recursion check of task_local_storage

[Qiliang Yuan]

test_recursion attaches on_enter to sys_enter and on_update to
bpf_local_storage_update, makes one syscall, and checks the task
storage values left behind and the recursion misses of both programs.

on_enter runs for every syscall of the system and returns early for
other tasks. On a preemptible kernel, a task can be preempted while it
runs on_enter, and a task entering a syscall on the same CPU then misses
the program. With other tests running in parallel, on_enter ends up
with recursion misses that have nothing to do with the test task, and
the check expecting none fails.

Drop the check. map_a holding 200, which only on_enter of the test task
writes, already shows that on_enter ran for it.

Fixes: 387b532138ee ("selftests/bpf: Tracing prog can still do lookup under busy lock")
Signed-off-by: Qiliang Yuan <odys.yuan@gmail.com>
---
 tools/testing/selftests/bpf/prog_tests/task_local_storage.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/task_local_storage.c b/tools/testing/selftests/bpf/prog_tests/task_local_storage.c
index 5b2b56cc3a4f3..c03ea94325d9e 100644
--- a/tools/testing/selftests/bpf/prog_tests/task_local_storage.c
+++ b/tools/testing/selftests/bpf/prog_tests/task_local_storage.c
@@ -138,12 +138,6 @@ static void test_recursion(void)
 	ASSERT_OK(err, "get prog info");
 	ASSERT_EQ(info.recursion_misses, 2, "on_update prog recursion");
 
-	prog_fd = bpf_program__fd(skel->progs.on_enter);
-	memset(&info, 0, sizeof(info));
-	err = bpf_prog_get_info_by_fd(prog_fd, &info, &info_len);
-	ASSERT_OK(err, "get prog info");
-	ASSERT_EQ(info.recursion_misses, 0, "on_enter prog recursion");
-
 out:
 	close(task_fd);
 	task_ls_recursion__destroy(skel);

---
base-commit: e1d84a37cba984388988d2f1ddc84561413f0db2
change-id: 20261009-selftests-bpf-task-ls-recursion-5a85b5d499ef

Best regards,
-- 
Qiliang Yuan <odys.yuan@gmail.com>

Re: [PATCH bpf-next] selftests/bpf: Drop the on_enter recursion check of task_local_storage

[Alexei Starovoitov]

On Thu, Oct 08, 2026 at 06:49 PM Qiliang Yuan <odys.yuan@gmail.com> wrote:
> other tasks. On a preemptible kernel, a task can be preempted while it
> runs on_enter, and a task entering a syscall on the same CPU then misses
> the program. With other tests running in parallel, on_enter ends up
> with recursion misses that have nothing to do with the test task, and
> the check expecting none fails.

Show the log of the failed run.
How many workers and how often does it fail?

> Drop the check. map_a holding 200, which only on_enter of the test task
> writes, already shows that on_enter ran for it.

The race works the other way too.
When another task is preempted inside on_enter and the test task calls
sys_gettid() on that cpu it's the test task that misses on_enter.
Nothing is created and "lookup map_a" fails with ENOENT.
enter_cnt == 2 in test_sys_enter_exit() has the same problem.

sys_enter is only a trigger here.
Make on_enter SEC("raw_tp") and run it with bpf_prog_test_run_opts()
like you did in enable_stats ?
Then no other task runs it and the check can stay.

> Fixes: 387b532138ee ("selftests/bpf: Tracing prog can still do lookup under busy lock")

Wrong tag. In 2022 the check was fine.
Progs attached to sys_enter were running with preemption disabled until
commit 439ebd5b5708 ("bpf: Add sleepable support for raw tracepoint programs").
Say that in the commit log.

pw-bot: cr