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Message-ID: <373e7e67-6ccc-5508-6937-6ea5a3eed5ea@redhat.com>
Date:   Thu, 13 Jul 2023 16:12:30 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Ryan Roberts <ryan.roberts@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        Mark Brown <broonie@...nel.org>,
        John Hubbard <jhubbard@...dia.com>,
        Florent Revest <revest@...omium.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v1 3/9] selftests/mm: Skip soft-dirty tests on arm64

On 13.07.23 16:09, 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@....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;
> +
>           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)
> 
> 

Oh, and if you want to have the skip, then you can think about 
converting test_softdirty() to only perform a single ksft_test_result(), 
and have a single skip on top.

All cleaner IMHO than ksft_test_result_if_softdirty ;)

-- 
Cheers,

David / dhildenb

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