linux-kernel - [PATCH v1] selftests/mm: cow: print ksft header before printing anything else

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Date:   Wed,  6 Dec 2023 11:35:58 +0100
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        David Hildenbrand <david@...hat.com>,
        Nico Pache <npache@...hat.com>
Subject: [PATCH v1] selftests/mm: cow: print ksft header before printing anything else

Doing a ksft_print_msg() before the ksft_print_header() seems to confuse
the ksft framework in a strange way: running the test on the cmdline
results in the expected output.

But piping the output somewhere else, results in some odd output,
whereby we repeatedly get the same info printed:
	# [INFO] detected THP size: 2048 KiB
	# [INFO] detected hugetlb page size: 2048 KiB
	# [INFO] detected hugetlb page size: 1048576 KiB
	# [INFO] huge zeropage is enabled
	TAP version 13
	1..190
	# [INFO] Anonymous memory tests in private mappings
	# [RUN] Basic COW after fork() ... with base page
	# [INFO] detected THP size: 2048 KiB
	# [INFO] detected hugetlb page size: 2048 KiB
	# [INFO] detected hugetlb page size: 1048576 KiB
	# [INFO] huge zeropage is enabled
	TAP version 13
	1..190
	# [INFO] Anonymous memory tests in private mappings
	# [RUN] Basic COW after fork() ... with base page
	ok 1 No leak from parent into child
	# [RUN] Basic COW after fork() ... with swapped out base page
	# [INFO] detected THP size: 2048 KiB
	# [INFO] detected hugetlb page size: 2048 KiB
	# [INFO] detected hugetlb page size: 1048576 KiB
	# [INFO] huge zeropage is enabled

Doing the ksft_print_header() first seems to resolve that and gives us
the output we expect:
	TAP version 13
	# [INFO] detected THP size: 2048 KiB
	# [INFO] detected hugetlb page size: 2048 KiB
	# [INFO] detected hugetlb page size: 1048576 KiB
	# [INFO] huge zeropage is enabled
	1..190
	# [INFO] Anonymous memory tests in private mappings
	# [RUN] Basic COW after fork() ... with base page
	ok 1 No leak from parent into child
	# [RUN] Basic COW after fork() ... with swapped out base page
	ok 2 No leak from parent into child
	# [RUN] Basic COW after fork() ... with THP
	ok 3 No leak from parent into child
	# [RUN] Basic COW after fork() ... with swapped-out THP
	ok 4 No leak from parent into child
	# [RUN] Basic COW after fork() ... with PTE-mapped THP
	ok 5 No leak from parent into child

Reported-by: Nico Pache <npache@...hat.com>
Fixes: f4b5fd6946e2 ("selftests/vm: anon_cow: THP tests")
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 tools/testing/selftests/mm/cow.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/mm/cow.c b/tools/testing/selftests/mm/cow.c
index 7324ce5363c0c..6f2f839904416 100644
--- a/tools/testing/selftests/mm/cow.c
+++ b/tools/testing/selftests/mm/cow.c
@@ -1680,6 +1680,8 @@ int main(int argc, char **argv)
 {
 	int err;
 
+	ksft_print_header();
+
 	pagesize = getpagesize();
 	thpsize = read_pmd_pagesize();
 	if (thpsize)
@@ -1689,7 +1691,6 @@ int main(int argc, char **argv)
 						    ARRAY_SIZE(hugetlbsizes));
 	detect_huge_zeropage();
 
-	ksft_print_header();
 	ksft_set_plan(ARRAY_SIZE(anon_test_cases) * tests_per_anon_test_case() +
 		      ARRAY_SIZE(anon_thp_test_cases) * tests_per_anon_thp_test_case() +
 		      ARRAY_SIZE(non_anon_test_cases) * tests_per_non_anon_test_case());
-- 
2.41.0