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

[David Hildenbrand]

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)


--
Cheers,

David / dhildenb