selftests: update ksm inheritance tests for prctl fork/exec

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/

Link: https://lkml.kernel.org/r/20251007182935207jm31wCIgLpZg5XbXQY64S@zte.com.cn
Signed-off-by: xu xin <xu.xin16@zte.com.cn>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jinjiang Tu <tujinjiang@huawei.com>
Cc: Stefan Roesch <shr@devkernel.io>
Cc: Wang Yaxin <wang.yaxin@zte.com.cn>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
index ac136f04b8d6537a4b3eb74934cf96ed36c34848..95afa5cfc062f463e434f35acbfbc8094bdf7fd5 100644 (file)
--- 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)