[PATCH bpf-next v2] 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>

---

v1->v2: reset skel->bss->target_pid to 0 before asserts (Amery)
v1: https://lore.kernel.org/bpf/20260224015855.1481707-1-ihor.solodrai@linux.dev/

---
 .../bpf/prog_tests/task_local_storage.c          | 16 +++++++++++-----
 1 file changed, 11 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..1b26c12f255a 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 +25,30 @@
 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");
+	skel->bss->target_pid = 0;
+
+	/* 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