[PATCH v1 2/2] mm/ksm: Test case for prctl fork/exec workflow

[Stefan Roesch <shr@devkernel.io>]

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.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 tools/testing/selftests/mm/Makefile           |  2 +
 .../selftests/mm/ksm_fork_exec_child.c        |  9 ++++
 .../selftests/mm/ksm_functional_tests.c       | 50 ++++++++++++++++++-
 3 files changed, 60 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/mm/ksm_fork_exec_child.c

diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index 6a9fc5693145..9ab6aa402544 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -73,6 +73,8 @@ ifneq ($(ARCH),arm64)
 TEST_GEN_PROGS += soft-dirty
 endif
 
+TEST_GEN_PROGS += ksm_fork_exec_child
+
 ifeq ($(ARCH),x86_64)
 CAN_BUILD_I386 := $(shell ./../x86/check_cc.sh "$(CC)" ../x86/trivial_32bit_program.c -m32)
 CAN_BUILD_X86_64 := $(shell ./../x86/check_cc.sh "$(CC)" ../x86/trivial_64bit_program.c)
diff --git a/tools/testing/selftests/mm/ksm_fork_exec_child.c b/tools/testing/selftests/mm/ksm_fork_exec_child.c
new file mode 100644
index 000000000000..298439f0d55f
--- /dev/null
+++ b/tools/testing/selftests/mm/ksm_fork_exec_child.c
@@ -0,0 +1,9 @@
+#include <sys/prctl.h>
+#include <stdlib.h>
+
+int main()
+{
+	/* Test if KSM is enabled for the process. */
+	int ksm = prctl(68, 0, 0, 0, 0);
+	exit(ksm == 1 ? 0 : 1);
+}
diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
index 901e950f9138..4dc0bb522c07 100644
--- a/tools/testing/selftests/mm/ksm_functional_tests.c
+++ b/tools/testing/selftests/mm/ksm_functional_tests.c
@@ -479,6 +479,53 @@ static void test_prctl_fork(void)
 	ksft_test_result_pass("PR_SET_MEMORY_MERGE value is inherited\n");
 }
 
+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 *filename = "./ksm_fork_exec_child";
+		char *argv_for_program[] = { filename, NULL };
+
+		execv(filename, argv_for_program);;
+	} else {
+		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;
+		}
+	}
+
+	ksft_test_result_pass("PR_SET_MEMORY_MERGE value is inherited\n");
+}
+
 static void test_prctl_unmerge(void)
 {
 	const unsigned int size = 2 * MiB;
@@ -536,7 +583,7 @@ static void test_prot_none(void)
 
 int main(int argc, char **argv)
 {
-	unsigned int tests = 7;
+	unsigned int tests = 8;
 	int err;
 
 #ifdef __NR_userfaultfd
@@ -576,6 +623,7 @@ int main(int argc, char **argv)
 
 	test_prctl();
 	test_prctl_fork();
+	test_prctl_fork_exec();
 	test_prctl_unmerge();
 
 	err = ksft_get_fail_cnt();
-- 
2.39.3