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Merge "init: use signalfd to catch SIGCHLD"

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Treehugger Robot 2018-04-12 22:49:27 +00:00 committed by Gerrit Code Review
commit 07de83831f
3 changed files with 54 additions and 72 deletions
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85
init/init.cpp
View file

@ -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() {
sigset_t mask;
sigemptyset(&mask);
sigaddset(&mask, SIGTERM);
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;
}
if (sigprocmask(SIG_UNBLOCK, &mask, nullptr) == -1) {
PLOG(FATAL) << "failed to unblock SIGTERM for PID " << getpid();
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 InstallSigtermHandler() {
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_BLOCK, &mask, nullptr) == -1) {
PLOG(FATAL) << "failed to block SIGTERM";
if (sigprocmask(SIG_UNBLOCK, &mask, nullptr) == -1) {
PLOG(FATAL) << "failed to unblock signals for PID " << getpid();
}
}
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);
}
// Register a handler to unblock SIGTERM in the child processes.
const int result = pthread_atfork(nullptr, nullptr, &UnblockSigterm);
if (sigprocmask(SIG_BLOCK, &mask, nullptr) == -1) {
PLOG(FATAL) << "failed to block signals";
}
// 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();

39
init/sigchld_handler.cpp
View file

@ -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

2
init/sigchld_handler.h
View file

@ -22,8 +22,6 @@ namespace init {
void ReapAnyOutstandingChildren();
void sigchld_handler_init(void);
} // namespace init
} // namespace android