Merge "init: use signalfd to catch SIGCHLD" (07de8383) · Commits · e / os / android_system_core

init/init.cpp

+50 −27

Original line number	Diff line number	Diff line
		@@ -79,7 +79,7 @@ static char qemu[32];
		std::string default_console = "/dev/console";

		static int epoll_fd = -1;
		static int sigterm_signal_fd = -1;
		static int signal_fd = -1;

		static std::unique_ptr<Timer> waiting_for_prop(nullptr);
		static std::string wait_prop_name;
		@@ -492,14 +492,7 @@ static void InstallRebootSignalHandlers() {
		sigaction(SIGTRAP, &action, nullptr);
		}

		static void HandleSigtermSignal() {
		signalfd_siginfo siginfo;
		ssize_t bytes_read = TEMP_FAILURE_RETRY(read(sigterm_signal_fd, &siginfo, sizeof(siginfo)));
		if (bytes_read != sizeof(siginfo)) {
		PLOG(ERROR) << "Failed to read siginfo from sigterm_signal_fd";
		return;
		}

		static void HandleSigtermSignal(const signalfd_siginfo& siginfo) {
		if (siginfo.ssi_pid != 0) {
		// Drop any userspace SIGTERM requests.
		LOG(DEBUG) << "Ignoring SIGTERM from pid " << siginfo.ssi_pid;
		@@ -509,37 +502,73 @@ static void HandleSigtermSignal() {
		HandlePowerctlMessage("shutdown,container");
		}

		static void UnblockSigterm() {
		static void HandleSignalFd() {
		signalfd_siginfo siginfo;
		ssize_t bytes_read = TEMP_FAILURE_RETRY(read(signal_fd, &siginfo, sizeof(siginfo)));
		if (bytes_read != sizeof(siginfo)) {
		PLOG(ERROR) << "Failed to read siginfo from signal_fd";
		return;
		}

		switch (siginfo.ssi_signo) {
		case SIGCHLD:
		ReapAnyOutstandingChildren();
		break;
		case SIGTERM:
		HandleSigtermSignal(siginfo);
		break;
		default:
		PLOG(ERROR) << "signal_fd: received unexpected signal " << siginfo.ssi_signo;
		break;
		}
		}

		static void UnblockSignals() {
		const struct sigaction act { .sa_handler = SIG_DFL };
		sigaction(SIGCHLD, &act, nullptr);

		sigset_t mask;
		sigemptyset(&mask);
		sigaddset(&mask, SIGCHLD);
		sigaddset(&mask, SIGTERM);

		if (sigprocmask(SIG_UNBLOCK, &mask, nullptr) == -1) {
		PLOG(FATAL) << "failed to unblock SIGTERM for PID " << getpid();
		PLOG(FATAL) << "failed to unblock signals for PID " << getpid();
		}
		}

		static void InstallSigtermHandler() {
		static void InstallSignalFdHandler() {
		// Applying SA_NOCLDSTOP to a defaulted SIGCHLD handler prevents the signalfd from receiving
		// SIGCHLD when a child process stops or continues (b/77867680#comment9).
		const struct sigaction act { .sa_handler = SIG_DFL, .sa_flags = SA_NOCLDSTOP };
		sigaction(SIGCHLD, &act, nullptr);

		sigset_t mask;
		sigemptyset(&mask);
		sigaddset(&mask, SIGCHLD);

		if (!IsRebootCapable()) {
		// If init does not have the CAP_SYS_BOOT capability, it is running in a container.
		// In that case, receiving SIGTERM will cause the system to shut down.
		sigaddset(&mask, SIGTERM);
		}

		if (sigprocmask(SIG_BLOCK, &mask, nullptr) == -1) {
		PLOG(FATAL) << "failed to block SIGTERM";
		PLOG(FATAL) << "failed to block signals";
		}

		// Register a handler to unblock SIGTERM in the child processes.
		const int result = pthread_atfork(nullptr, nullptr, &UnblockSigterm);
		// Register a handler to unblock signals in the child processes.
		const int result = pthread_atfork(nullptr, nullptr, &UnblockSignals);
		if (result != 0) {
		LOG(FATAL) << "Failed to register a fork handler: " << strerror(result);
		}

		sigterm_signal_fd = signalfd(-1, &mask, SFD_CLOEXEC);
		if (sigterm_signal_fd == -1) {
		PLOG(FATAL) << "failed to create signalfd for SIGTERM";
		signal_fd = signalfd(-1, &mask, SFD_CLOEXEC);
		if (signal_fd == -1) {
		PLOG(FATAL) << "failed to create signalfd";
		}

		register_epoll_handler(sigterm_signal_fd, HandleSigtermSignal);
		register_epoll_handler(signal_fd, HandleSignalFd);
		}

		int main(int argc, char** argv) {
		@@ -682,13 +711,7 @@ int main(int argc, char** argv) {
		PLOG(FATAL) << "epoll_create1 failed";
		}

		sigchld_handler_init();

		if (!IsRebootCapable()) {
		// If init does not have the CAP_SYS_BOOT capability, it is running in a container.
		// In that case, receiving SIGTERM will cause the system to shut down.
		InstallSigtermHandler();
		}
		InstallSignalFdHandler();

		property_load_boot_defaults();
		export_oem_lock_status();

init/sigchld_handler.cpp

+0 −39

Original line number	Diff line number	Diff line
		@@ -39,9 +39,6 @@ using android::base::make_scope_guard;
		namespace android {
		namespace init {

		static int signal_write_fd = -1;
		static int signal_read_fd = -1;

		static bool ReapOneProcess() {
		siginfo_t siginfo = {};
		// This returns a zombie pid or informs us that there are no zombies left to be reaped.
		@@ -102,46 +99,10 @@ static bool ReapOneProcess() {
		return true;
		}

		static void handle_signal() {
		// Clear outstanding requests.
		char buf[32];
		read(signal_read_fd, buf, sizeof(buf));

		ReapAnyOutstandingChildren();
		}

		static void SIGCHLD_handler(int) {
		if (TEMP_FAILURE_RETRY(write(signal_write_fd, "1", 1)) == -1) {
		PLOG(ERROR) << "write(signal_write_fd) failed";
		}
		}

		void ReapAnyOutstandingChildren() {
		while (ReapOneProcess()) {
		}
		}

		void sigchld_handler_init() {
		// Create a signalling mechanism for SIGCHLD.
		int s[2];
		if (socketpair(AF_UNIX, SOCK_STREAM \| SOCK_NONBLOCK \| SOCK_CLOEXEC, 0, s) == -1) {
		PLOG(FATAL) << "socketpair failed in sigchld_handler_init";
		}

		signal_write_fd = s[0];
		signal_read_fd = s[1];

		// Write to signal_write_fd if we catch SIGCHLD.
		struct sigaction act;
		memset(&act, 0, sizeof(act));
		act.sa_handler = SIGCHLD_handler;
		act.sa_flags = SA_NOCLDSTOP;
		sigaction(SIGCHLD, &act, 0);

		ReapAnyOutstandingChildren();

		register_epoll_handler(signal_read_fd, handle_signal);
		}

		} // namespace init
		} // namespace android

init/sigchld_handler.h

+0 −2

Original line number	Diff line number	Diff line
		@@ -22,8 +22,6 @@ namespace init {

		void ReapAnyOutstandingChildren();

		void sigchld_handler_init(void);

		} // namespace init
		} // namespace android