Re: [PATCH v2 5/7] selftests/mm: Fix child process exit codes in ksm_functional_tests

[David Hildenbrand]

On 03.07.25 10:51, Donet Tom wrote:
> Hi David
>
> On 7/3/25 2:03 PM, David Hildenbrand wrote:
> > On 03.07.25 08:06, Aboorva Devarajan wrote:
> > > In ksm_functional_tests, test_child_ksm() returned negative values
> > > to indicate errors. However, when passed to exit(), these were
> > > interpreted as large unsigned values (e.g, -2 became 254), leading to
> > > incorrect handling in the parent process. As a result, some tests
> > > appeared to be skipped or silently failed.
> > >
> > > This patch changes test_child_ksm() to return positive error codes
> > > (1, 2, 3) and updates test_child_ksm_err() to interpret them correctly.
> > > This ensures the parent accurately detects and reports child process
> > > failures.
> > >
> > > --------------
> > > Before patch:
> > > --------------
> > > - [RUN] test_unmerge
> > > ok 1 Pages were unmerged
> > > ...
> > > - [RUN] test_prctl_fork
> > > - No pages got merged
> > > - [RUN] test_prctl_fork_exec
> > > ok 7 PR_SET_MEMORY_MERGE value is inherited
> > > ...
> > > Bail out! 1 out of 8 tests failed
> > > - Planned tests != run tests (9 != 8)
> > > - Totals: pass:7 fail:1 xfail:0 xpass:0 skip:0 error:0
> > >
> > > --------------
> > > After patch:
> > > --------------
> > > - [RUN] test_unmerge
> > > ok 1 Pages were unmerged
> > > ...
> > > - [RUN] test_prctl_fork
> > > - No pages got merged
> > > not ok 7 Merge in child failed
> > > - [RUN] test_prctl_fork_exec
> > > ok 8 PR_SET_MEMORY_MERGE value is inherited
> > > ...
> > > Bail out! 2 out of 9 tests failed
> > > - Totals: pass:7 fail:2 xfail:0 xpass:0 skip:0 error:0
> > >
> > > Fixes: 6c47de3be3a0 ("selftest/mm: ksm_functional_tests: extend test
> > > case for ksm fork/exec")
> > > Signed-off-by: Aboorva Devarajan <aboorvad@xxxxxxxxxxxxx>
> >
> > BTW, when I run the test, I get this weird output
> >
> > TAP version 13
> > 1..9
> > # [RUN] test_unmerge
> > ok 1 Pages were unmerged
> > # [RUN] test_unmerge_zero_pages
> > ok 2 KSM zero pages were unmerged
> > # [RUN] test_unmerge_discarded
> > ok 3 Pages were unmerged
> > # [RUN] test_unmerge_uffd_wp
> > ok 4 Pages were unmerged
> > # [RUN] test_prot_none
> > ok 5 Pages were unmerged
> > # [RUN] test_prctl
> > ok 6 Setting/clearing PR_SET_MEMORY_MERGE works
> > # [RUN] test_prctl_fork
> > ok 7 PR_SET_MEMORY_MERGE value is inherited
> > # [RUN] test_prctl_fork_exec
> >
> > ^ where is the test?
> >
> > # [RUN] test_prctl_unmerge
> > ok 8 Pages were unmerged
> > # Planned tests != run tests (9 != 8)
> > # Totals: pass:8 fail:0 xfail:0 xpass:0 skip:0 error:0
> >
> > ^ what?
> >
> > ok 8 PR_SET_MEMORY_MERGE value is inherited
> > # [RUN] test_prctl_unmerge
> > ok 9 Pages were unmerged
> > # Totals: pass:9 fail:0 xfail:0 xpass:0 skip:0 error:0
> >
> > ^ huh, what now?
>
> The problem with the exec test is that it uses its own binary to exec.
>
>           } else if (child_pid == 0) {
>                   char *prg_name = "./ksm_functional_tests";
>                   char *argv_for_program[] = { prg_name,
> FORK_EXEC_CHILD_PRG_NAME, NULL };
>
>                   execv(prg_name, argv_for_program);
>                   return;
>           }
> > So we should run it on the same directory where the binary present.

So, I assume the execv fails. We should handle that, and figure out why 
it fails.

diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c 
b/tools/testing/selftests/mm/ksm_functional_tests.c
index d8bd1911dfc0a..0ddbb390df33b 100644
--- a/tools/testing/selftests/mm/ksm_functional_tests.c
+++ b/tools/testing/selftests/mm/ksm_functional_tests.c
@@ -527,6 +527,8 @@ static void test_child_ksm_err(int status)
                ksft_test_result_fail("Merge in child failed\n");
        else if (status == -3)
                ksft_test_result_skip("Merge in child skipped\n");
+       else if (status == 4)
+               ksft_test_result_fail("Binary not found\n");
 }

 /* Verify that prctl ksm flag is inherited. */
@@ -598,7 +600,7 @@ static void test_prctl_fork_exec(void)
                char *argv_for_program[] = { prg_name, 
FORK_EXEC_CHILD_PRG_NAME };

                execv(prg_name, argv_for_program);
-               return;
+               exit(4);
        }

        if (waitpid(child_pid, &status, 0) > 0) {

results in

TAP version 13
1..9
# [RUN] test_unmerge
ok 1 Pages were unmerged
# [RUN] test_unmerge_zero_pages
ok 2 KSM zero pages were unmerged
# [RUN] test_unmerge_discarded
ok 3 Pages were unmerged
# [RUN] test_unmerge_uffd_wp
ok 4 Pages were unmerged
# [RUN] test_prot_none
ok 5 Pages were unmerged
# [RUN] test_prctl
ok 6 Setting/clearing PR_SET_MEMORY_MERGE works
# [RUN] test_prctl_fork
ok 7 PR_SET_MEMORY_MERGE value is inherited
# [RUN] test_prctl_fork_exec
not ok 8 Binary not found
# [RUN] test_prctl_unmerge
ok 9 Pages were unmerged
Bail out! 1 out of 9 tests failed
# Totals: pass:8 fail:1 xfail:0 xpass:0 skip:0 error:0


--
Cheers,

David / dhildenb