linux-kernel - Re: [PATCH v2 5/7] selftests/mm: Fix child process exit codes in ksm_functional

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Message-ID: <42c0135a-dbd9-47e1-9b9e-c36c147a2315@redhat.com>
Date: Thu, 3 Jul 2025 11:14:32 +0200
From: David Hildenbrand <david@...hat.com>
To: Donet Tom <donettom@...ux.ibm.com>,
 Aboorva Devarajan <aboorvad@...ux.ibm.com>, akpm@...ux-foundation.org,
 Liam.Howlett@...cle.com, lorenzo.stoakes@...cle.com, shuah@...nel.org,
 pfalcato@...e.de, ziy@...dia.com, baolin.wang@...ux.alibaba.com,
 npache@...hat.com, ryan.roberts@....com, dev.jain@....com, baohua@...nel.org
Cc: linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
 linux-kernel@...r.kernel.org, ritesh.list@...il.com
Subject: Re: [PATCH v2 5/7] selftests/mm: Fix child process exit codes in
 ksm_functional_tests

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@...ux.ibm.com>
>>
>> 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