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

[David Hildenbrand]

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@xxxxxxx>
> > > > ---
> > > >     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