perf daemon: Add signalfd support

Use a signalfd fd to track SIGCHLD signals as notifications for perf
session termination.

This way we don't need to actively check for child status, being
notified if there's change.

Suggested-by: Alexei Budankov <abudankov@huawei.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: https://lore.kernel.org/r/20210208200908.1019149-10-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-daemon.c

@@ -9,6 +9,7 @@
 #include <string.h>
 #include <signal.h>
 #include <stdlib.h>
+#include <time.h>
 #include <stdio.h>
 #include <unistd.h>
 #include <errno.h>
@@ -18,6 +19,8 @@
 #include <sys/socket.h>
 #include <sys/un.h>
 #include <sys/stat.h>
+#include <sys/signalfd.h>
+#include <sys/wait.h>
 #include <poll.h>
 #include <sys/stat.h>
 #include "builtin.h"
@@ -83,6 +86,7 @@ struct daemon {
 	struct list_head	 sessions;
 	FILE			*out;
 	char			 perf[PATH_MAX];
+	int			 signal_fd;
 };
 
 static struct daemon __daemon = {
@@ -368,6 +372,116 @@ static int daemon_session__run(struct daemon_session *session,
 	return -1;
 }
 
+static pid_t handle_signalfd(struct daemon *daemon)
+{
+	struct daemon_session *session;
+	struct signalfd_siginfo si;
+	ssize_t err;
+	int status;
+	pid_t pid;
+
+	err = read(daemon->signal_fd, &si, sizeof(struct signalfd_siginfo));
+	if (err != sizeof(struct signalfd_siginfo))
+		return -1;
+
+	list_for_each_entry(session, &daemon->sessions, list) {
+
+		if (session->pid != (int) si.ssi_pid)
+			continue;
+
+		pid = waitpid(session->pid, &status, 0);
+		if (pid == session->pid) {
+			if (WIFEXITED(status)) {
+				pr_info("session '%s' exited, status=%d\n",
+					session->name, WEXITSTATUS(status));
+			} else if (WIFSIGNALED(status)) {
+				pr_info("session '%s' killed (signal %d)\n",
+					session->name, WTERMSIG(status));
+			} else if (WIFSTOPPED(status)) {
+				pr_info("session '%s' stopped (signal %d)\n",
+					session->name, WSTOPSIG(status));
+			} else {
+				pr_info("session '%s' Unexpected status (0x%x)\n",
+					session->name, status);
+			}
+		}
+
+		session->state = KILL;
+		session->pid = -1;
+		return pid;
+	}
+
+	return 0;
+}
+
+static int daemon_session__wait(struct daemon_session *session, struct daemon *daemon,
+				int secs)
+{
+	struct pollfd pollfd = {
+		.fd	= daemon->signal_fd,
+		.events	= POLLIN,
+	};
+	pid_t wpid = 0, pid = session->pid;
+	time_t start;
+
+	start = time(NULL);
+
+	do {
+		int err = poll(&pollfd, 1, 1000);
+
+		if (err > 0) {
+			wpid = handle_signalfd(daemon);
+		} else if (err < 0) {
+			perror("failed: poll\n");
+			return -1;
+		}
+
+		if (start + secs < time(NULL))
+			return -1;
+	} while (wpid != pid);
+
+	return 0;
+}
+
+static bool daemon__has_alive_session(struct daemon *daemon)
+{
+	struct daemon_session *session;
+
+	list_for_each_entry(session, &daemon->sessions, list) {
+		if (session->pid != -1)
+			return true;
+	}
+
+	return false;
+}
+
+static int daemon__wait(struct daemon *daemon, int secs)
+{
+	struct pollfd pollfd = {
+		.fd	= daemon->signal_fd,
+		.events	= POLLIN,
+	};
+	time_t start;
+
+	start = time(NULL);
+
+	do {
+		int err = poll(&pollfd, 1, 1000);
+
+		if (err > 0) {
+			handle_signalfd(daemon);
+		} else if (err < 0) {
+			perror("failed: poll\n");
+			return -1;
+		}
+
+		if (start + secs < time(NULL))
+			return -1;
+	} while (daemon__has_alive_session(daemon));
+
+	return 0;
+}
+
 static int setup_server_socket(struct daemon *daemon)
 {
 	struct sockaddr_un addr;
@@ -493,9 +607,14 @@ static int daemon_session__signal(struct daemon_session *session, int sig)
 	return kill(session->pid, sig);
 }
 
-static void daemon_session__kill(struct daemon_session *session)
+static void daemon_session__kill(struct daemon_session *session,
+				 struct daemon *daemon)
 {
 	daemon_session__signal(session, SIGTERM);
+	if (daemon_session__wait(session, daemon, 10)) {
+		daemon_session__signal(session, SIGKILL);
+		daemon_session__wait(session, daemon, 10);
+	}
 }
 
 static void daemon__signal(struct daemon *daemon, int sig)
@@ -523,6 +642,10 @@ static void daemon_session__remove(struct daemon_session *session)
 static void daemon__kill(struct daemon *daemon)
 {
 	daemon__signal(daemon, SIGTERM);
+	if (daemon__wait(daemon, 10)) {
+		daemon__signal(daemon, SIGKILL);
+		daemon__wait(daemon, 10);
+	}
 }
 
 static void daemon__exit(struct daemon *daemon)
@@ -549,7 +672,7 @@ static int daemon__reconfig(struct daemon *daemon)
 		/* Remove session. */
 		if (session->state == KILL) {
 			if (session->pid > 0) {
-				daemon_session__kill(session);
+				daemon_session__kill(session, daemon);
 				pr_info("reconfig: session '%s' killed\n", session->name);
 			}
 			daemon_session__remove(session);
@@ -558,7 +681,7 @@ static int daemon__reconfig(struct daemon *daemon)
 
 		/* Reconfig session. */
 		if (session->pid > 0) {
-			daemon_session__kill(session);
+			daemon_session__kill(session, daemon);
 			pr_info("reconfig: session '%s' killed\n", session->name);
 		}
 		if (daemon_session__run(session, daemon))
@@ -724,6 +847,20 @@ static int go_background(struct daemon *daemon)
 	return 0;
 }
 
+static int setup_signalfd(struct daemon *daemon)
+{
+	sigset_t mask;
+
+	sigemptyset(&mask);
+	sigaddset(&mask, SIGCHLD);
+
+	if (sigprocmask(SIG_BLOCK, &mask, NULL) == -1)
+		return -1;
+
+	daemon->signal_fd = signalfd(-1, &mask, SFD_NONBLOCK|SFD_CLOEXEC);
+	return daemon->signal_fd;
+}
+
 static int __cmd_start(struct daemon *daemon, struct option parent_options[],
 		       int argc, const char **argv)
 {
@@ -733,8 +870,8 @@ static int __cmd_start(struct daemon *daemon, struct option parent_options[],
 		OPT_PARENT(parent_options),
 		OPT_END()
 	};
-	int sock_fd = -1, conf_fd = -1;
-	int sock_pos, file_pos;
+	int sock_fd = -1, conf_fd = -1, signal_fd = -1;
+	int sock_pos, file_pos, signal_pos;
 	struct fdarray fda;
 	int err = 0;
 
@@ -766,7 +903,7 @@ static int __cmd_start(struct daemon *daemon, struct option parent_options[],
 
 	pr_info("daemon started (pid %d)\n", getpid());
 
-	fdarray__init(&fda, 2);
+	fdarray__init(&fda, 3);
 
 	sock_fd = setup_server_socket(daemon);
 	if (sock_fd < 0)
@@ -776,6 +913,10 @@ static int __cmd_start(struct daemon *daemon, struct option parent_options[],
 	if (conf_fd < 0)
 		goto out;
 
+	signal_fd = setup_signalfd(daemon);
+	if (signal_fd < 0)
+		goto out;
+
 	sock_pos = fdarray__add(&fda, sock_fd, POLLIN|POLLERR|POLLHUP, 0);
 	if (sock_pos < 0)
 		goto out;
@@ -784,6 +925,10 @@ static int __cmd_start(struct daemon *daemon, struct option parent_options[],
 	if (file_pos < 0)
 		goto out;
 
+	signal_pos = fdarray__add(&fda, signal_fd, POLLIN|POLLERR|POLLHUP, 0);
+	if (signal_pos < 0)
+		goto out;
+
 	signal(SIGINT, sig_handler);
 	signal(SIGTERM, sig_handler);
 
@@ -797,6 +942,8 @@ static int __cmd_start(struct daemon *daemon, struct option parent_options[],
 				err = handle_server_socket(daemon, sock_fd);
 			if (fda.entries[file_pos].revents & POLLIN)
 				err = handle_config_changes(daemon, conf_fd, &reconfig);
+			if (fda.entries[signal_pos].revents & POLLIN)
+				err = handle_signalfd(daemon) < 0;
 
 			if (reconfig)
 				err = setup_server_config(daemon);
@@ -813,6 +960,8 @@ static int __cmd_start(struct daemon *daemon, struct option parent_options[],
 		close(sock_fd);
 	if (conf_fd != -1)
 		close(conf_fd);
+	if (conf_fd != -1)
+		close(signal_fd);
 
 	pr_info("daemon exited\n");
 	fclose(daemon->out);