selftests/mm: add messages about test errors to the cow tests

It is not sufficiently clear what the individual tests in the cow test
program are checking so add messages for the failure cases.

Link: https://lkml.kernel.org/r/20250610-selftest-mm-cow-tweaks-v1-4-43cd7457500f@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>
Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 20 insertions, 8 deletions

diff --git a/tools/testing/selftests/mm/cow.c b/tools/testing/selftests/mm/cow.c
index 48fcf03aa4cd..29767e2afdd0 100644
--- a/tools/testing/selftests/mm/cow.c
+++ b/tools/testing/selftests/mm/cow.c
@@ -268,8 +268,10 @@ static void do_test_cow_in_parent(char *mem, size_t size, bool do_mprotect,
 		 * fail because (a) harder to fix and (b) nobody really cares.
 		 * Flag them as expected failure for now.
 		 */
+		ksft_print_msg("Leak from parent into child\n");
 		log_test_result(KSFT_XFAIL);
 	} else {
+		ksft_print_msg("Leak from parent into child\n");
 		log_test_result(KSFT_FAIL);
 	}
 close_comm_pipes:
@@ -397,8 +399,10 @@ static void do_test_vmsplice_in_parent(char *mem, size_t size,
 		 * fail because (a) harder to fix and (b) nobody really cares.
 		 * Flag them as expected failure for now.
 		 */
+		ksft_print_msg("Leak from child into parent\n");
 		log_test_result(KSFT_XFAIL);
 	} else {
+		ksft_print_msg("Leak from child into parent\n");
 		log_test_result(KSFT_FAIL);
 	}
 close_pipe:
@@ -570,10 +574,12 @@ static void do_test_iouring(char *mem, size_t size, bool use_fork)
 	}
 
 	/* Finally, check if we read what we expected. */
-	if (!memcmp(mem, tmp, size))
+	if (!memcmp(mem, tmp, size)) {
 		log_test_result(KSFT_PASS);
-	else
+	} else {
+		ksft_print_msg("Longtom R/W pin is not reliable\n");
 		log_test_result(KSFT_FAIL);
+	}
 
 quit_child:
 	if (use_fork) {
@@ -725,10 +731,12 @@ static void do_test_ro_pin(char *mem, size_t size, enum ro_pin_test test,
 		ksft_perror("PIN_LONGTERM_TEST_READ failed");
 		log_test_result(KSFT_FAIL);
 	} else {
-		if (!memcmp(mem, tmp, size))
+		if (!memcmp(mem, tmp, size)) {
 			log_test_result(KSFT_PASS);
-		else
+		} else {
+			ksft_print_msg("Longterm R/O pin is not reliable\n");
 			log_test_result(KSFT_FAIL);
+		}
 	}
 
 	ret = ioctl(gup_fd, PIN_LONGTERM_TEST_STOP);
@@ -1417,10 +1425,12 @@ static void do_test_anon_thp_collapse(char *mem, size_t size,
 	else
 		ret = -EINVAL;
 
-	if (!ret)
+	if (!ret) {
 		log_test_result(KSFT_PASS);
-	else
+	} else {
+		ksft_print_msg("Leak from parent into child\n");
 		log_test_result(KSFT_FAIL);
+	}
 close_comm_pipes:
 	close_comm_pipes(&comm_pipes);
 }
@@ -1528,10 +1538,12 @@ static void test_cow(char *mem, const char *smem, size_t size)
 	memset(mem, 0xff, size);
 
 	/* See if we still read the old values via the other mapping. */
-	if (!memcmp(smem, old, size))
+	if (!memcmp(smem, old, size)) {
 		log_test_result(KSFT_PASS);
-	else
+	} else {
+		ksft_print_msg("Other mapping modified\n");
 		log_test_result(KSFT_FAIL);
+	}
 	free(old);
 }