Re: [PATCH bpf 1/2] selftests/bpf: Fix timing-dependent assertions in task work stress test

[luyun <luyun_611@163.com>]

在 2026/9/17 17:00, bot+bpf-ci@kernel.org 写道:
>> task_work_run() assumes every stress run observes both scheduler
>> contention and, when the delete thread is enabled, cancellation of at
>> least one pending callback.
>>
>> Neither outcome is guaranteed. Contention is observed only when another
>> scheduler selects the same one of 128 map values while its task work is
>> outstanding. A valid run can therefore have no scheduling errors. This
>> was reproduced with a single scheduler: more than one million callbacks
>> were scheduled and completed while schedule_error remained zero.
> This isn't a bug, but would it read more clearly to say something like 'the
> task_work_stress test helper' (or name the file) instead of the bare
> task_work_run() in the opening sentence?  There are three functions with
> that name in the tree: kernel/task_work.c, prog_tests/test_task_work.c, and
> the static helper being changed here in prog_tests/task_work_stress.c, so
> the bare name could be mistaken for the kernel function on first reading.
Agreed. The opening sentence will be reworded to "The task_work_run()
helper in prog_tests/task_work_stress.c assumes ...", so it cannot be
mistaken for the kernel function of the same name.
> This isn't a bug, but was nthreads reduced locally to get the
> single-scheduler run quoted here? The test hardcodes 'int nthreads = 16;'
> (prog_tests/task_work_stress.c:50) and the only environment knob is
> BPF_TASK_WORK_TEST_TIME for the duration. A reader trying to reproduce the
> quoted numbers has no way to get there without editing the file. It might
> help to say so explicitly, or give the 16-thread numbers, since the test
> has no knob for the thread count.
Yes, that run came from a modified copy of the test with the scheduler
thread count reduced to 1. v2 will state this explicitly: "reproduced
with a modified copy of the test running a single scheduler thread
(nthreads is hardcoded to 16 and the test has no knob for it)".

These are commit message changes only; the code will be identical to
v1, and 2/2 is unchanged. If there are no further comments on the two
patches, I will send out v2 later.

Thanks,
Yun Lu
>> Likewise, a successful map deletion may remove a value after its
>> callback has completed. delete_success can therefore be nonzero without
>> callback_success being smaller than callback_scheduled.
>>
>> Drop the assertion that schedule_error is nonzero. Keep requiring exact
>> callback accounting when deletion is disabled. With deletion enabled,
>> allow equal counts but still reject callback_success greater than
>> callback_scheduled.
>>
>> Fixes: c6ae18e0af5e ("selftests/bpf: add bpf task work stress tests")
>> Signed-off-by: Yun Lu <luyun@kylinos.cn>
>
> ---
> AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
> See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
>
> CI run summary: https://github.com/kernel-patches/bpf/actions/runs/35199472874