[PATCH linux-next v2 2/2] selftests: update ksm inheritation tests for prctl fork/exec

[<xu.xin16@zte.com.cn>]

From: xu xin <xu.xin16@zte.com.cn>

To reproduce the issue mentioned by [1], this add a setting of pages_to_scan
and sleep_millisecs at the start of test_prctl_fork_exec(). The main change
is just raise the scanning frequency of ksmd.

[1] https://lore.kernel.org/all/202510012256278259zrhgATlLA2C510DMD3qI@zte.com.cn/

Signed-off-by: xu xin <xu.xin16@zte.com.cn>
---
 .../selftests/mm/ksm_functional_tests.c       | 57 +++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
index ac136f04b8d6..95afa5cfc062 100644
--- a/tools/testing/selftests/mm/ksm_functional_tests.c
+++ b/tools/testing/selftests/mm/ksm_functional_tests.c
@@ -38,6 +38,8 @@ enum ksm_merge_mode {
 };

 static int mem_fd;
+static int pages_to_scan_fd;
+static int sleep_millisecs_fd;
 static int pagemap_fd;
 static size_t pagesize;

@@ -493,6 +495,46 @@ static void test_prctl_fork(void)
 	ksft_test_result_pass("PR_SET_MEMORY_MERGE value is inherited\n");
 }

+static int start_ksmd_and_set_frequency(char *pages_to_scan, char *sleep_ms)
+{
+	int ksm_fd;
+
+	ksm_fd = open("/sys/kernel/mm/ksm/run", O_RDWR);
+	if (ksm_fd < 0)
+		return -errno;
+
+	if (write(ksm_fd, "1", 1) != 1)
+		return -errno;
+
+	if (write(pages_to_scan_fd, pages_to_scan, strlen(pages_to_scan)) <= 0)
+		return -errno;
+
+	if (write(sleep_millisecs_fd, sleep_ms, strlen(sleep_ms)) <= 0)
+		return -errno;
+
+	return 0;
+}
+
+static int stop_ksmd_and_restore_frequency(void)
+{
+	int ksm_fd;
+
+	ksm_fd = open("/sys/kernel/mm/ksm/run", O_RDWR);
+	if (ksm_fd < 0)
+		return -errno;
+
+	if (write(ksm_fd, "2", 1) != 1)
+		return -errno;
+
+	if (write(pages_to_scan_fd, "100", 3) <= 0)
+		return -errno;
+
+	if (write(sleep_millisecs_fd, "20", 2) <= 0)
+		return -errno;
+
+	return 0;
+}
+
 static void test_prctl_fork_exec(void)
 {
 	int ret, status;
@@ -500,6 +542,9 @@ static void test_prctl_fork_exec(void)

 	ksft_print_msg("[RUN] %s\n", __func__);

+	if (start_ksmd_and_set_frequency("2000", "0"))
+		ksft_test_result_fail("set ksmd's scanning frequency failed\n");
+
 	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");
@@ -542,6 +587,11 @@ static void test_prctl_fork_exec(void)
 		return;
 	}

+	if (stop_ksmd_and_restore_frequency()) {
+		ksft_test_result_fail("restore ksmd frequency failed\n");
+		return;
+	}
+
 	ksft_test_result_pass("PR_SET_MEMORY_MERGE value is inherited\n");
 }

@@ -656,6 +706,13 @@ static void init_global_file_handles(void)
 		ksft_exit_skip("open(\"/proc/self/pagemap\") failed\n");
 	if (ksm_get_self_merging_pages() < 0)
 		ksft_exit_skip("accessing \"/proc/self/ksm_merging_pages\") failed\n");
+
+	pages_to_scan_fd = open("/sys/kernel/mm/ksm/pages_to_scan", O_RDWR);
+	if (pages_to_scan_fd < 0)
+		ksft_exit_fail_msg("opening /sys/kernel/mm/ksm/pages_to_scan failed\n");
+	sleep_millisecs_fd = open("/sys/kernel/mm/ksm/sleep_millisecs", O_RDWR);
+	if (sleep_millisecs_fd < 0)
+		ksft_exit_fail_msg("opening /sys/kernel/mm/ksm/sleep_millisecs failed\n");
 }

 int main(int argc, char **argv)
-- 
2.25.1