[PATCH bpf-next v1] selftests/bpf: Fix flakiness of task_local_storage/sys_enter_exit

[Ihor Solodrai <ihor.solodrai@linux.dev>]

The test_sys_enter_exit test was setting target_pid before attaching
the BPF programs, which causes syscalls made during the attach phase
to be counted. This is flaky because, apparently, there is no
guarantee that both on_enter and on_exit will trigger during the
attachment.

Move the target_pid assignment to after task_local_storage__attach()
so that only explicit sys_gettid() calls are counted.

Reported-by: BPF CI Bot (Claude Opus 4.6) <bot+bpf-ci@kernel.org>
Closes: https://github.com/kernel-patches/vmtest/issues/448
Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>

---

I've been experimenting with running AI on BPF CI to investigate test
failures. This is an example of a thing it may come up with.

I don't want to spam the list with these, so for starters I'll be
relaying only patches that I evaluated and/or tested.

The AI generated reports will be posted with "[bpf-ci-bot]" prefix
here: https://github.com/kernel-patches/vmtest/issues

The goal of this particular application of AI is to make BPF CI more
stable, less noisy/flaky, and potentially find and fix more kernel
bugs. We'll see how it goes.

---
 .../selftests/bpf/prog_tests/task_local_storage.c  | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 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 7bee33797c71..2820a604aaa6 100644
--- a/tools/testing/selftests/bpf/prog_tests/task_local_storage.c
+++ b/tools/testing/selftests/bpf/prog_tests/task_local_storage.c
@@ -25,24 +25,28 @@
 static void test_sys_enter_exit(void)
 {
 	struct task_local_storage *skel;
+	pid_t pid = sys_gettid();
 	int err;
 
 	skel = task_local_storage__open_and_load();
 	if (!ASSERT_OK_PTR(skel, "skel_open_and_load"))
 		return;
 
-	skel->bss->target_pid = sys_gettid();
-
 	err = task_local_storage__attach(skel);
 	if (!ASSERT_OK(err, "skel_attach"))
 		goto out;
 
+	/* Set target_pid after attach so that syscalls made during
+	 * attach are not counted.
+	 */
+	skel->bss->target_pid = pid;
+
 	sys_gettid();
 	sys_gettid();
 
-	/* 3x syscalls: 1x attach and 2x gettid */
-	ASSERT_EQ(skel->bss->enter_cnt, 3, "enter_cnt");
-	ASSERT_EQ(skel->bss->exit_cnt, 3, "exit_cnt");
+	/* 2x gettid syscalls */
+	ASSERT_EQ(skel->bss->enter_cnt, 2, "enter_cnt");
+	ASSERT_EQ(skel->bss->exit_cnt, 2, "exit_cnt");
 	ASSERT_EQ(skel->bss->mismatch_cnt, 0, "mismatch_cnt");
 out:
 	task_local_storage__destroy(skel);
-- 
2.53.0