Re: [PATCH v1 3/9] selftests/mm: Skip soft-dirty tests on arm64

[Ryan Roberts <ryan.roberts@arm.com>]

On 13/07/2023 15:09, David Hildenbrand wrote:
> On 13.07.23 16:03, Ryan Roberts wrote:
>> On 13/07/2023 14:56, David Hildenbrand wrote:
>>> On 13.07.23 15:54, Ryan Roberts wrote:
>>>> arm64 does not support the soft-dirty PTE bit. However there are tests
>>>> in `madv_populate` and `soft-dirty` which assume it is supported and
>>>> cause spurious failures to be reported when preferred behaviour would be
>>>> to mark the tests as skipped.
>>>>
>>>> Unfortunately, the only way to determine if the soft-dirty dirty bit is
>>>> supported is to write to a page, then see if the bit is set in
>>>> /proc/self/pagemap. But the tests that we want to conditionally execute
>>>> are testing precicesly this. So if we introduced this feature check, we
>>>> could accedentally turn a real failure (on a system that claims to
>>>> support soft-dirty) into a skip.
>>>>
>>>> So instead, do the check based on architecture; for arm64, we report
>>>> that soft-dirty is not supported. This is wrapped up into a utility
>>>> function `system_has_softdirty()`, which is used to skip the whole
>>>> `soft-dirty` suite, and mark the soft-dirty tests in the `madv_populate`
>>>> suite as skipped.
>>>>
>>>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>>>> ---
>>>>    tools/testing/selftests/mm/madv_populate.c | 18 +++++++++++++-----
>>>>    tools/testing/selftests/mm/soft-dirty.c    |  3 +++
>>>>    tools/testing/selftests/mm/vm_util.c       | 17 +++++++++++++++++
>>>>    tools/testing/selftests/mm/vm_util.h       |  1 +
>>>>    4 files changed, 34 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/tools/testing/selftests/mm/madv_populate.c
>>>> b/tools/testing/selftests/mm/madv_populate.c
>>>> index 60547245e479..5a8c176d7fec 100644
>>>> --- a/tools/testing/selftests/mm/madv_populate.c
>>>> +++ b/tools/testing/selftests/mm/madv_populate.c
>>>> @@ -232,6 +232,14 @@ static bool range_is_not_softdirty(char *start, ssize_t
>>>> size)
>>>>        return ret;
>>>>    }
>>>>
>>>> +#define ksft_test_result_if_softdirty(cond, ...)    \
>>>> +do {                            \
>>>> +    if (system_has_softdirty())            \
>>>> +        ksft_test_result(cond, __VA_ARGS__);    \
>>>> +    else                        \
>>>> +        ksft_test_result_skip(__VA_ARGS__);    \
>>>> +} while (0)
>>>> +
>>>>    static void test_softdirty(void)
>>>>    {
>>>>        char *addr;
>>>> @@ -246,19 +254,19 @@ static void test_softdirty(void)
>>>>
>>>>        /* Clear any softdirty bits. */
>>>>        clear_softdirty();
>>>> -    ksft_test_result(range_is_not_softdirty(addr, SIZE),
>>>> +    ksft_test_result_if_softdirty(range_is_not_softdirty(addr, SIZE),
>>>>                 "range is not softdirty\n");
>>>>
>>>>        /* Populating READ should set softdirty. */
>>>>        ret = madvise(addr, SIZE, MADV_POPULATE_READ);
>>>> -    ksft_test_result(!ret, "MADV_POPULATE_READ\n");
>>>> -    ksft_test_result(range_is_not_softdirty(addr, SIZE),
>>>> +    ksft_test_result_if_softdirty(!ret, "MADV_POPULATE_READ\n");
>>>> +    ksft_test_result_if_softdirty(range_is_not_softdirty(addr, SIZE),
>>>>                 "range is not softdirty\n");
>>>>
>>>>        /* Populating WRITE should set softdirty. */
>>>>        ret = madvise(addr, SIZE, MADV_POPULATE_WRITE);
>>>> -    ksft_test_result(!ret, "MADV_POPULATE_WRITE\n");
>>>> -    ksft_test_result(range_is_softdirty(addr, SIZE),
>>>> +    ksft_test_result_if_softdirty(!ret, "MADV_POPULATE_WRITE\n");
>>>> +    ksft_test_result_if_softdirty(range_is_softdirty(addr, SIZE),
>>>>                 "range is softdirty\n");
>>>
>>> We probably want to skip the whole test_*softdirty* test instead of adding this
>>> (IMHO suboptimal) ksft_test_result_if_softdirty.
>>
>> Yeah I thought about doing it that way, but then the output just looks like
>> there were fewer tests and they all passed. But thinking about it now, I guess
>> the TAP header outputs the number of planned tests and the number of tests
>> executed are fewer, so a machine parser would still notice. I just don't like
>> that it outputs skipped:0.
>>
>> But it a lightly held view. Happy to just do:
>>
>>     if (system_has_softdirty())
>>         test_softdirty()
>>
>> If you insist. ;-)
> 
> diff --git a/tools/testing/selftests/mm/madv_populate.c
> b/tools/testing/selftests/mm/madv_populate.c
> index 60547245e479..33fda0337b32 100644
> --- a/tools/testing/selftests/mm/madv_populate.c
> +++ b/tools/testing/selftests/mm/madv_populate.c
> @@ -266,12 +266,16 @@ static void test_softdirty(void)
>  
>  int main(int argc, char **argv)
>  {
> +       int nr_tests = 16;
>         int err;
>  
>         pagesize = getpagesize();
>  
> +       if (system_has_softdirty())
> +               nr_tests += 5;

This is the opposite of the point I was trying to make; If there are 21 tests in
a suite, I'd like to know that there are 21 tests, 16 of which passed and 5 of
which were skipped. This will hide the 5 from the test report.

> +
>         ksft_print_header();
> -       ksft_set_plan(21);
> +       ksft_set_plan(nr_tests);
>  
>         sense_support();
>         test_prot_read();
> @@ -279,7 +283,8 @@ int main(int argc, char **argv)
>         test_holes();
>         test_populate_read();
>         test_populate_write();
> -       test_softdirty();
> +       if (system_has_softdirty())
> +               test_softdirty();
>  
>         err = ksft_get_fail_cnt();
>         if (err)
> 
>