--- move-to-control-group.cpp	2018-09-14 21:48:55.000000000 +0800
+++ move-to-control-group.new.cpp	2019-11-25 10:50:20.518459398 +0800
@@ -50,9 +50,8 @@
 	next_prog = arg0_of(args);
 
 	FileStar self_cgroup(open_my_control_group_info("/proc/self/cgroup"));
-	if (!self_cgroup) {
+	if (!self_cgroup && ENOENT != errno) {  // `ENOENT == error' is what we'll see on a BSD.
 		const int error(errno);
-		if (ENOENT == error) return;	// This is what we'll see on a BSD.
 		std::fprintf(stderr, "%s: FATAL: %s: %s\n", prog, "/proc/self/cgroup", std::strerror(error));
 		throw EXIT_FAILURE;
 	}
@@ -73,20 +72,16 @@
 
 	current = prefix + current;
 
-	if (0 > mkdirat(AT_FDCWD, current.c_str(), 0755)) {
+	if (0 > mkdirat(AT_FDCWD, current.c_str(), 0755) && EEXIST != error) {
 		const int error(errno);
-		if (EEXIST != error) {
-			std::fprintf(stderr, "%s: FATAL: %s: %s\n", prog, current.c_str(), std::strerror(error));
-			throw EXIT_FAILURE;
-		}
+		std::fprintf(stderr, "%s: FATAL: %s: %s\n", prog, current.c_str(), std::strerror(error));
+		throw EXIT_FAILURE;
 	}
 
 	const FileDescriptorOwner cgroup_procs_fd(open_appendexisting_at(AT_FDCWD, (current + "/cgroup.procs").c_str()));
-	if (0 > cgroup_procs_fd.get()) {
-procs_file_error:
+	if (0 > cgroup_procs_fd.get() || 0 > write(cgroup_procs_fd.get(), "0\n", 2)) {
 		const int error(errno);
 		std::fprintf(stderr, "%s: FATAL: %s%s: %s\n", prog, current.c_str(), "/cgroup.procs", std::strerror(error));
 		throw EXIT_FAILURE;
 	}
-	if (0 > write(cgroup_procs_fd.get(), "0\n", 2)) goto procs_file_error;
 }