mm/ksm: test case for prctl fork/exec workflow

This adds a new test case to the ksm functional tests to make sure that
the KSM setting is inherited by the child process when doing a fork/exec.

Link: https://lkml.kernel.org/r/20230922211141.320789-3-shr@devkernel.io
Signed-off-by: Stefan Roesch <shr@devkernel.io>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Carl Klemm <carl@uvos.xyz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: Stefan Roesch

tools/testing/selftests/mm/ksm_functional_tests.c

@@ -26,6 +26,7 @@
 
 #define KiB 1024u
 #define MiB (1024 * KiB)
+#define FORK_EXEC_CHILD_PRG_NAME "ksm_fork_exec_child"
 
 static int mem_fd;
 static int ksm_fd;
@@ -479,6 +480,64 @@ static void test_prctl_fork(void)
 	ksft_test_result_pass("PR_SET_MEMORY_MERGE value is inherited\n");
 }
 
+static int ksm_fork_exec_child(void)
+{
+	/* Test if KSM is enabled for the process. */
+	return prctl(PR_GET_MEMORY_MERGE, 0, 0, 0, 0) == 1;
+}
+
+static void test_prctl_fork_exec(void)
+{
+	int ret, status;
+	pid_t child_pid;
+
+	ksft_print_msg("[RUN] %s\n", __func__);
+
+	ret = prctl(PR_SET_MEMORY_MERGE, 1, 0, 0, 0);
+	if (ret < 0 && errno == EINVAL) {
+		ksft_test_result_skip("PR_SET_MEMORY_MERGE not supported\n");
+		return;
+	} else if (ret) {
+		ksft_test_result_fail("PR_SET_MEMORY_MERGE=1 failed\n");
+		return;
+	}
+
+	child_pid = fork();
+	if (child_pid == -1) {
+		ksft_test_result_skip("fork() failed\n");
+		return;
+	} else if (child_pid == 0) {
+		char *prg_name = "./ksm_functional_tests";
+		char *argv_for_program[] = { prg_name, FORK_EXEC_CHILD_PRG_NAME };
+
+		execv(prg_name, argv_for_program);
+		return;
+	}
+
+	if (waitpid(child_pid, &status, 0) > 0) {
+		if (WIFEXITED(status)) {
+			status = WEXITSTATUS(status);
+			if (status) {
+				ksft_test_result_fail("KSM not enabled\n");
+				return;
+			}
+		} else {
+			ksft_test_result_fail("program didn't terminate normally\n");
+			return;
+		}
+	} else {
+		ksft_test_result_fail("waitpid() failed\n");
+		return;
+	}
+
+	if (prctl(PR_SET_MEMORY_MERGE, 0, 0, 0, 0)) {
+		ksft_test_result_fail("PR_SET_MEMORY_MERGE=0 failed\n");
+		return;
+	}
+
+	ksft_test_result_pass("PR_SET_MEMORY_MERGE value is inherited\n");
+}
+
 static void test_prctl_unmerge(void)
 {
 	const unsigned int size = 2 * MiB;
@@ -536,9 +595,13 @@ static void test_prot_none(void)
 
 int main(int argc, char **argv)
 {
-	unsigned int tests = 7;
+	unsigned int tests = 8;
 	int err;
 
+	if (argc > 1 && !strcmp(argv[1], FORK_EXEC_CHILD_PRG_NAME)) {
+		exit(ksm_fork_exec_child() == 1 ? 0 : 1);
+	}
+
 #ifdef __NR_userfaultfd
 	tests++;
 #endif
@@ -576,6 +639,7 @@ int main(int argc, char **argv)
 
 	test_prctl();
 	test_prctl_fork();
+	test_prctl_fork_exec();
 	test_prctl_unmerge();
 
 	err = ksft_get_fail_cnt();