[RFC PATCH v2 18/19] selftests/vm: add KSM fork test

[Stefan Roesch <shr@devkernel.io>]

Add fork test to verify that the MMF_VM_MERGE_ANY flag is inherited by
the child process.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 tools/testing/selftests/mm/ksm_tests.c | 53 +++++++++++++++++++++++++-
 1 file changed, 51 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/mm/ksm_tests.c b/tools/testing/selftests/mm/ksm_tests.c
index 9667cb3b8c6a..a0a48ac43b29 100644
--- a/tools/testing/selftests/mm/ksm_tests.c
+++ b/tools/testing/selftests/mm/ksm_tests.c
@@ -44,6 +44,7 @@ enum ksm_merge_type {
 
 enum ksm_test_name {
 	CHECK_KSM_MERGE,
+	CHECK_KSM_MERGE_FORK,
 	CHECK_KSM_UNMERGE,
 	CHECK_KSM_GET_MERGE_TYPE,
 	CHECK_KSM_ZERO_PAGE_MERGE,
@@ -126,7 +127,8 @@ static void print_help(void)
 	       "    For this test, the size of duplicated memory area (in MiB)\n"
 	       "    must be provided using -s option\n"
 	       " -C evaluate the time required to break COW of merged pages.\n"
-	       " -G query merge mode\n\n");
+	       " -G query merge mode\n"
+	       " -F evaluate that the KSM process flag is inherited\n\n");
 
 	printf(" -a: specify the access protections of pages.\n"
 	       "     <prot> must be of the form [rwx].\n"
@@ -325,6 +327,47 @@ static int check_ksm_merge(int merge_type, int mapping, int prot,
 	return KSFT_FAIL;
 }
 
+/* Verify that prctl ksm flag is inherited. */
+static int check_ksm_fork(void)
+{
+	int rc = KSFT_FAIL;
+	pid_t child_pid;
+
+	if (prctl(PR_SET_MEMORY_MERGE, 1)) {
+		perror("prctl");
+		return KSFT_FAIL;
+	}
+
+	child_pid = fork();
+	if (child_pid == 0) {
+		int is_on = prctl(PR_GET_MEMORY_MERGE, 0);
+
+		if (!is_on)
+			exit(KSFT_FAIL);
+
+		exit(KSFT_PASS);
+	}
+
+	if (child_pid < 0)
+		goto out;
+
+	if (waitpid(child_pid, &rc, 0) < 0)
+		rc = KSFT_FAIL;
+
+	if (prctl(PR_SET_MEMORY_MERGE, 0)) {
+		perror("prctl");
+		rc = KSFT_FAIL;
+	}
+
+out:
+	if (rc == KSFT_PASS)
+		printf("OK\n");
+	else
+		printf("Not OK\n");
+
+	return rc;
+}
+
 static int check_ksm_get_merge_type(void)
 {
 	if (prctl(PR_SET_MEMORY_MERGE, 1)) {
@@ -760,7 +803,7 @@ int main(int argc, char *argv[])
 	bool merge_across_nodes = KSM_MERGE_ACROSS_NODES_DEFAULT;
 	long size_MB = 0;
 
-	while ((opt = getopt(argc, argv, "ha:p:l:z:m:s:t:GMUZNPCHD")) != -1) {
+	while ((opt = getopt(argc, argv, "ha:p:l:z:m:s:t:FGMUZNPCHD")) != -1) {
 		switch (opt) {
 		case 'a':
 			prot = str_to_prot(optarg);
@@ -811,6 +854,9 @@ int main(int argc, char *argv[])
 				merge_type = atoi(optarg);
 			}
 			break;
+		case 'F':
+			test_name = CHECK_KSM_MERGE_FORK;
+			break;
 		case 'M':
 			break;
 		case 'U':
@@ -867,6 +913,9 @@ int main(int argc, char *argv[])
 		ret = check_ksm_merge(merge_type, MAP_PRIVATE | MAP_ANONYMOUS, prot, page_count,
 				      ksm_scan_limit_sec, page_size);
 		break;
+	case CHECK_KSM_MERGE_FORK:
+		ret = check_ksm_fork();
+		break;
 	case CHECK_KSM_UNMERGE:
 		ret = check_ksm_unmerge(merge_type, MAP_PRIVATE | MAP_ANONYMOUS, prot,
 					ksm_scan_limit_sec, page_size);
-- 
2.30.2