Re: [PATCH] selftests: Make ksft_exit functions return void instead of int

[Shuah Khan <skhan@linuxfoundation.org>]

On 4/24/24 09:05, Nathan Chancellor wrote:
> On Wed, Apr 24, 2024 at 07:44:31AM -0600, Shuah Khan wrote:
>> On 4/17/24 09:37, Nathan Chancellor wrote:
>>> Commit f7d5bcd35d42 ("selftests: kselftest: Mark functions that
>>> unconditionally call exit() as __noreturn") marked functions that call
>>> exit() as __noreturn but it did not change the return type of these
>>> functions from 'void' to 'int' like it should have (since a noreturn
>>> function by definition cannot return an integer because it does not
>>> return...) because there are many tests that return the result of the
>>> ksft_exit function, even though it has never been used due to calling
>>> exit().
>>>
>>> Prior to adding __noreturn, the compiler would not know that the functions
>>> that call exit() will not return, so code like
>>>
>>>     void ksft_exit_fail(void)
>>>     {
>>>       exit(1);
>>>     }
>>>
>>>     void ksft_exit_pass(void)
>>>     {
>>>       exit(0);
>>>     }
>>>
>>>     int main(void)
>>>     {
>>>       int ret;
>>>
>>>       ret = foo();
>>>       if (ret)
>>>         ksft_exit_fail();
>>>       ksft_exit_pass();
>>>     }
>>>
>>> would cause the compiler to complain that main() does not return an
>>> integer, even though when ksft_exit_pass() is called, exit() will cause
>>> the program to terminate. So ksft_exit_...() returns int to make the
>>> compiler happy.
>>>
>>>     int ksft_exit_fail(void)
>>>     {
>>>       exit(1);
>>>     }
>>>
>>>     int ksft_exit_pass(void)
>>>     {
>>>       exit(0);
>>>     }
>>>
>>>     int main(void)
>>>     {
>>>       int ret;
>>>
>>>       ret = foo();
>>>       if (ret)
>>>         return ksft_exit_fail();
>>>       return ksft_exit_pass();
>>>     }
>>>
>>> While this results in no warnings, it is weird semantically and it has
>>> issues as noted in the aforementioned __noreturn change. Now that
>>> __noreturn has been added to these functions, it is much cleaner to
>>> change the functions to 'void' and eliminate the return statements, as
>>> it has been made clear to the compiler that these functions terminate
>>> the program. Drop the return before all instances of ksft_exit_...() in
>>> a mechanical way. Only two manually changes were made to transform
>>>
>>>     return !ret ? ksft_exit_pass() : ksft_exit_fail();
>>>
>>> into the more idiomatic
>>>
>>>     if (ret)
>>>       ksft_exit_fail();
>>>     ksft_exit_pass();
>>>
>>> as well as a few style clean ups now that the code is shorter.
>>>
>>> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
>>> ---
>>>    tools/testing/selftests/clone3/clone3_clear_sighand.c        |  2 +-
>>>    tools/testing/selftests/clone3/clone3_set_tid.c              |  4 +++-
>>>    tools/testing/selftests/ipc/msgque.c                         | 11 +++++------
>>>    tools/testing/selftests/kselftest.h                          | 12 ++++++------
>>>    .../selftests/membarrier/membarrier_test_multi_thread.c      |  2 +-
>>>    .../selftests/membarrier/membarrier_test_single_thread.c     |  2 +-
>>>    tools/testing/selftests/mm/compaction_test.c                 |  6 +++---
>>>    tools/testing/selftests/mm/cow.c                             |  2 +-
>>>    tools/testing/selftests/mm/gup_longterm.c                    |  2 +-
>>>    tools/testing/selftests/mm/gup_test.c                        |  4 ++--
>>>    tools/testing/selftests/mm/ksm_functional_tests.c            |  2 +-
>>>    tools/testing/selftests/mm/madv_populate.c                   |  2 +-
>>>    tools/testing/selftests/mm/mkdirty.c                         |  2 +-
>>>    tools/testing/selftests/mm/pagemap_ioctl.c                   |  4 ++--
>>>    tools/testing/selftests/mm/soft-dirty.c                      |  2 +-
>>>    tools/testing/selftests/pidfd/pidfd_fdinfo_test.c            |  2 +-
>>>    tools/testing/selftests/pidfd/pidfd_open_test.c              |  4 +++-
>>>    tools/testing/selftests/pidfd/pidfd_poll_test.c              |  2 +-
>>>    tools/testing/selftests/pidfd/pidfd_test.c                   |  2 +-
>>>    tools/testing/selftests/resctrl/resctrl_tests.c              |  6 +++---
>>>    tools/testing/selftests/sync/sync_test.c                     |  3 +--
>>>    tools/testing/selftests/timers/adjtick.c                     |  4 ++--
>>>    tools/testing/selftests/timers/alarmtimer-suspend.c          |  4 ++--
>>>    tools/testing/selftests/timers/change_skew.c                 |  4 ++--
>>>    tools/testing/selftests/timers/freq-step.c                   |  4 ++--
>>>    tools/testing/selftests/timers/leap-a-day.c                  | 10 +++++-----
>>>    tools/testing/selftests/timers/leapcrash.c                   |  4 ++--
>>>    tools/testing/selftests/timers/mqueue-lat.c                  |  4 ++--
>>>    tools/testing/selftests/timers/posix_timers.c                | 12 ++++++------
>>>    tools/testing/selftests/timers/raw_skew.c                    |  6 +++---
>>>    tools/testing/selftests/timers/set-2038.c                    |  4 ++--
>>>    tools/testing/selftests/timers/set-tai.c                     |  4 ++--
>>>    tools/testing/selftests/timers/set-timer-lat.c               |  4 ++--
>>>    tools/testing/selftests/timers/set-tz.c                      |  4 ++--
>>>    tools/testing/selftests/timers/skew_consistency.c            |  4 ++--
>>>    tools/testing/selftests/timers/threadtest.c                  |  2 +-
>>>    tools/testing/selftests/timers/valid-adjtimex.c              |  6 +++---
>>>    tools/testing/selftests/x86/lam.c                            |  2 +-
>>>    38 files changed, 81 insertions(+), 79 deletions(-)
>>>
>>
>> Please generate separate patches for each test so it is easy to apply
>> them and also reduce merge conflicts.
> 
> Is applying 30+ patches easier than applying just one? It is not a
> trivial amount of work for me to break this series up into individual
> patches but I will do so if you really want me to. I based this on the
> kselftest tree directly so that it would apply cleanly.
> 

I am not asking each file to be a separate patch.
> How does breaking apart the changes reduce merge conflicts? The diff is
> going to be the same and semantic conflicts can still occur due to the
> kselftest.h changes.

selftest patches go through various repos. With this patch touching
several tests, there will be conflicts with multiple trees.

If this patch can't be split due to dependency on kselftest.h, I will
pull it in, but I do need you to include all the maintainers.

> 
>> You are missing maintainers for clone3, mm, pidfd tests. I can take these
>> through kselftest tree, but I need the changes split.
> 
> Fair enough, I should have CC'd them, although given this is a change to
> the kselftest API, I was not sure they would care too much.
> 

The reason for cc'ing the maintainers is to keep them in the loop about this
change that could result in merge conflicts between kselftest tree and theirs.

Besides I would rather not have developers make calls on who should or shouldn't
care about a change. :)

thanks,
-- Shuah