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.
Additionally, test_prctl_fork_exec() now uses exit(4) after a failed
execv() to clearly signal exec failures. 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")
Co-developed-by: Donet Tom <donettom@linux.ibm.com>
Signed-off-by: Donet Tom <donettom@linux.ibm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
---
.../testing/selftests/mm/ksm_functional_tests.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)
diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
index 996dc6645570..534aa405cac7 100644
--- a/tools/testing/selftests/mm/ksm_functional_tests.c
+++ b/tools/testing/selftests/mm/ksm_functional_tests.c
@@ -512,14 +512,14 @@ static int test_child_ksm(void)
/* Test if KSM is enabled for the process. */
if (prctl(PR_GET_MEMORY_MERGE, 0, 0, 0, 0) != 1)
- return -1;
+ return 1;
/* Test if merge could really happen. */
map = __mmap_and_merge_range(0xcf, size, PROT_READ | PROT_WRITE, KSM_MERGE_NONE);
if (map == MAP_MERGE_FAIL)
- return -2;
+ return 2;
else if (map == MAP_MERGE_SKIP)
- return -3;
+ return 3;
ksm_unmerge();
munmap(map, size);
@@ -528,12 +528,14 @@ static int test_child_ksm(void)
static void test_child_ksm_err(int status)
{
- if (status == -1)
+ if (status == 1)
ksft_test_result_fail("unexpected PR_GET_MEMORY_MERGE result in child\n");
- else if (status == -2)
+ else if (status == 2)
ksft_test_result_fail("Merge in child failed\n");
- else if (status == -3)
+ 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. */
@@ -606,7 +608,7 @@ static void test_prctl_fork_exec(void)
char *argv_for_program[] = { prg_name, FORK_EXEC_CHILD_PRG_NAME, NULL };
execv(prg_name, argv_for_program);
- return;
+ exit(4);
}
if (waitpid(child_pid, &status, 0) > 0) {
--
2.47.1On Sat, Aug 16, 2025 at 09:31:11AM +0530, 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 is because "the least significant 8 bits" is returned to parent, right?
>
>This patch changes test_child_ksm() to return positive error codes (1, 2,
>3) and updates test_child_ksm_err() to interpret them correctly.
>Additionally, test_prctl_fork_exec() now uses exit(4) after a failed
>execv() to clearly signal exec failures. 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")
>Co-developed-by: Donet Tom <donettom@linux.ibm.com>
>Signed-off-by: Donet Tom <donettom@linux.ibm.com>
>Acked-by: David Hildenbrand <david@redhat.com>
>Signed-off-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
If so:
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Thanks, I am afraid to make the same mistake if you don't point out.
--
Wei Yang
Help you, Help me
On Sat, 2025-08-16 at 14:43 +0000, Wei Yang wrote:
Hi Wei,
> On Sat, Aug 16, 2025 at 09:31:11AM +0530, 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 is because "the least significant 8 bits" is returned to parent, right?
>
>
Yes, that's right. As per the WEXITSTATUS(wstatus) manual:
WEXITSTATUS: returns the exit status of the child. This consists of the
least significant 8 bits of the status argument that the child
specified in a call to exit(3) or _exit(2) or as the argument for a
return statement in main(). This macro should only be employed if
WIFEXITED returned true.
Since only the least significant 8 bits are preserved, negative return
values can appear as large unsigned codes, so using small positive exit
codes ensures the parent interprets the error code correctly.
> > This patch changes test_child_ksm() to return positive error codes (1, 2,
> > 3) and updates test_child_ksm_err() to interpret them correctly.
> > Additionally, test_prctl_fork_exec() now uses exit(4) after a failed
> > execv() to clearly signal exec failures. 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")
> > Co-developed-by: Donet Tom <donettom@linux.ibm.com>
> > Signed-off-by: Donet Tom <donettom@linux.ibm.com>
> > Acked-by: David Hildenbrand <david@redhat.com>
> > Signed-off-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
>
> If so:
>
> Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
>
> Thanks, I am afraid to make the same mistake if you don't point out.
Thanks,
Aboorva
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