cgfsng: do MS_REMOUNT

Perform MS_REMOUNT on mounts with MS_RDONLY.

Signed-off-by: LiFeng <lifeng68@huawei.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

src/lxc/cgroups/cgfsng.c

@@ -1947,6 +1947,15 @@ static int do_secondstage_mounts_if_needed(int type, struct hierarchy *h,
 				cgpath);
 		return -1;
 	}
+
+	if (flags & MS_RDONLY) {
+		if (mount(sourcepath, cgpath, "cgroup", MS_REMOUNT | flags | MS_RDONLY, NULL) < 0) {
+			free(sourcepath);
+			SYSERROR("Error remounting %s read-only", cgpath);
+			return -1;
+		}
+	}
+
 	free(sourcepath);
 	INFO("Completed second stage cgroup automounts for %s", cgpath);
 	return 0;