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

Link: https://lkml.kernel.org/r/20231206103558.38040-1-david@redhat.com
Fixes: f4b5fd69 ("selftests/vm: anon_cow: THP tests")
Signed-off-by: David Hildenbrand <david@redhat.com>
Reported-by: Nico Pache <npache@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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());