Re: [PATCH bpf-next v2] selftests/bpf: Fix flakiness of task_local_storage/sys_enter_exit

["Emil Tsalapatis" <emil@etsalapatis.com>]

On Tue Feb 24, 2026 at 4:12 PM EST, Ihor Solodrai wrote:
> 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>
>

Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>

> ---
>
> 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);