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

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

On 2/24/26 2:04 PM, Amery Hung wrote:
> On Tue, Feb 24, 2026 at 1:12 PM Ihor Solodrai <ihor.solodrai@linux.dev> 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>
>>
>> ---
>>
>> 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");
> 
> Does tools/testing/selftests/bpf/prog_tests/cgrp_local_storage.c also
> have the same flakiness issue and should also be updated in the same
> way?

I haven't seen similar failures on CI, but that may just mean we were
lucky.

Do you know of other tests that may have the same issue?

I checked these, but only task_local_storage and cgrp_local_storage
assert counts:

$ grep -r 'skel->bss->target_pid = .*gettid' tools/testing/selftests/bpf/
tools/testing/selftests/bpf/prog_tests/cgroup_xattr.c:  skel->bss->target_pid = sys_gettid();
tools/testing/selftests/bpf/prog_tests/rcu_read_lock.c: skel->bss->target_pid = sys_gettid();
tools/testing/selftests/bpf/prog_tests/rcu_read_lock.c: skel->bss->target_pid = sys_gettid();
tools/testing/selftests/bpf/prog_tests/task_local_storage.c:    skel->bss->target_pid = sys_gettid();
tools/testing/selftests/bpf/prog_tests/cgrp_local_storage.c:    skel->bss->target_pid = sys_gettid();
tools/testing/selftests/bpf/prog_tests/cgrp_local_storage.c:    skel->bss->target_pid = sys_gettid();


> 
>>         ASSERT_EQ(skel->bss->mismatch_cnt, 0, "mismatch_cnt");
>>  out:
>>         task_local_storage__destroy(skel);
>> --
>> 2.53.0
>>