Merge pull request #7045 from mjstapp/fix_signals

lib: Resolve signal handling race in event loop

lib/sigevent.c

@@ -63,6 +63,33 @@ static void quagga_signal_handler(int signo)
 	sigmaster.caught = 1;
 }
 
+/*
+ * Check whether any signals have been received and are pending. This is done
+ * with the application's key signals blocked. The complete set of signals
+ * is returned in 'setp', so the caller can restore them when appropriate.
+ * If there are pending signals, returns 'true', 'false' otherwise.
+ */
+bool frr_sigevent_check(sigset_t *setp)
+{
+	sigset_t blocked;
+	int i;
+	bool ret;
+
+	sigemptyset(setp);
+	sigemptyset(&blocked);
+
+	/* Set up mask of application's signals */
+	for (i = 0; i < sigmaster.sigc; i++)
+		sigaddset(&blocked, sigmaster.signals[i].signal);
+
+	pthread_sigmask(SIG_BLOCK, &blocked, setp);
+
+	/* Now that the application's signals are blocked, test. */
+	ret = (sigmaster.caught != 0);
+
+	return ret;
+}
+
 /* check if signals have been caught and run appropriate handlers */
 int quagga_sigevent_process(void)
 {

lib/sigevent.h

@@ -48,6 +48,15 @@ struct quagga_signal_t {
 extern void signal_init(struct thread_master *m, int sigc,
 			struct quagga_signal_t *signals);
 
+
+/*
+ * Check whether any signals have been received and are pending. This is done
+ * with the application's key signals blocked. The complete set of signals
+ * is returned in 'setp', so the caller can restore them when appropriate.
+ * If there are pending signals, returns 'true', 'false' otherwise.
+ */
+bool frr_sigevent_check(sigset_t *setp);
+
 /* check whether there are signals to handle, process any found */
 extern int quagga_sigevent_process(void);
 

lib/thread.c

@@ -728,9 +728,13 @@ static void thread_free(struct thread_master *master, struct thread *thread)
 	XFREE(MTYPE_THREAD, thread);
 }
 
-static int fd_poll(struct thread_master *m, struct pollfd *pfds, nfds_t pfdsize,
-		   nfds_t count, const struct timeval *timer_wait)
+static int fd_poll(struct thread_master *m, const struct timeval *timer_wait,
+		   bool *eintr_p)
 {
+	sigset_t origsigs;
+	unsigned char trash[64];
+	nfds_t count = m->handler.copycount;
+
 	/*
 	 * If timer_wait is null here, that means poll() should block
 	 * indefinitely, unless the thread_master has overridden it by setting
@@ -761,15 +765,58 @@ static int fd_poll(struct thread_master *m, struct pollfd *pfds, nfds_t pfdsize,
 	rcu_assert_read_unlocked();
 
 	/* add poll pipe poker */
-	assert(count + 1 < pfdsize);
-	pfds[count].fd = m->io_pipe[0];
-	pfds[count].events = POLLIN;
-	pfds[count].revents = 0x00;
+	assert(count + 1 < m->handler.pfdsize);
+	m->handler.copy[count].fd = m->io_pipe[0];
+	m->handler.copy[count].events = POLLIN;
+	m->handler.copy[count].revents = 0x00;
 
-	num = poll(pfds, count + 1, timeout);
+	/* We need to deal with a signal-handling race here: we
+	 * don't want to miss a crucial signal, such as SIGTERM or SIGINT,
+	 * that may arrive just before we enter poll(). We will block the
+	 * key signals, then check whether any have arrived - if so, we return
+	 * before calling poll(). If not, we'll re-enable the signals
+	 * in the ppoll() call.
+	 */
 
-	unsigned char trash[64];
-	if (num > 0 && pfds[count].revents != 0 && num--)
+	sigemptyset(&origsigs);
+	if (m->handle_signals) {
+		/* Main pthread that handles the app signals */
+		if (frr_sigevent_check(&origsigs)) {
+			/* Signal to process - restore signal mask and return */
+			pthread_sigmask(SIG_SETMASK, &origsigs, NULL);
+			num = -1;
+			*eintr_p = true;
+			goto done;
+		}
+	} else {
+		/* Don't make any changes for the non-main pthreads */
+		pthread_sigmask(SIG_SETMASK, NULL, &origsigs);
+	}
+
+#if defined(HAVE_PPOLL)
+	struct timespec ts, *tsp;
+
+	if (timeout >= 0) {
+		ts.tv_sec = timeout / 1000;
+		ts.tv_nsec = (timeout % 1000) * 1000000;
+		tsp = &ts;
+	} else
+		tsp = NULL;
+
+	num = ppoll(m->handler.copy, count + 1, tsp, &origsigs);
+	pthread_sigmask(SIG_SETMASK, &origsigs, NULL);
+#else
+	/* Not ideal - there is a race after we restore the signal mask */
+	pthread_sigmask(SIG_SETMASK, &origsigs, NULL);
+	num = poll(m->handler.copy, count + 1, timeout);
+#endif
+
+done:
+
+	if (num < 0 && errno == EINTR)
+		*eintr_p = true;
+
+	if (num > 0 && m->handler.copy[count].revents != 0 && num--)
 		while (read(m->io_pipe[0], &trash, sizeof(trash)) > 0)
 			;
 
@@ -1434,7 +1481,7 @@ struct thread *thread_fetch(struct thread_master *m, struct thread *fetch)
 	struct timeval zerotime = {0, 0};
 	struct timeval tv;
 	struct timeval *tw = NULL;
-
+	bool eintr_p = false;
 	int num = 0;
 
 	do {
@@ -1506,14 +1553,14 @@ struct thread *thread_fetch(struct thread_master *m, struct thread *fetch)
 
 		pthread_mutex_unlock(&m->mtx);
 		{
-			num = fd_poll(m, m->handler.copy, m->handler.pfdsize,
-				      m->handler.copycount, tw);
+			eintr_p = false;
+			num = fd_poll(m, tw, &eintr_p);
 		}
 		pthread_mutex_lock(&m->mtx);
 
 		/* Handle any errors received in poll() */
 		if (num < 0) {
-			if (errno == EINTR) {
+			if (eintr_p) {
 				pthread_mutex_unlock(&m->mtx);
 				/* loop around to signal handler */
 				continue;
@@ -1703,3 +1750,49 @@ void funcname_thread_execute(struct thread_master *m,
 	/* Give back or free thread. */
 	thread_add_unuse(m, thread);
 }
+
+/* Debug signal mask - if 'sigs' is NULL, use current effective mask. */
+void debug_signals(const sigset_t *sigs)
+{
+	int i, found;
+	sigset_t tmpsigs;
+	char buf[300];
+
+	/*
+	 * We're only looking at the non-realtime signals here, so we need
+	 * some limit value. Platform differences mean at some point we just
+	 * need to pick a reasonable value.
+	 */
+#if defined SIGRTMIN
+#  define LAST_SIGNAL SIGRTMIN
+#else
+#  define LAST_SIGNAL 32
+#endif
+
+
+	if (sigs == NULL) {
+		sigemptyset(&tmpsigs);
+		pthread_sigmask(SIG_BLOCK, NULL, &tmpsigs);
+		sigs = &tmpsigs;
+	}
+
+	found = 0;
+	buf[0] = '\0';
+
+	for (i = 0; i < LAST_SIGNAL; i++) {
+		char tmp[20];
+
+		if (sigismember(sigs, i) > 0) {
+			if (found > 0)
+				strlcat(buf, ",", sizeof(buf));
+			snprintf(tmp, sizeof(tmp), "%d", i);
+			strlcat(buf, tmp, sizeof(buf));
+			found++;
+		}
+	}
+
+	if (found == 0)
+		snprintf(buf, sizeof(buf), "<none>");
+
+	zlog_debug("%s: %s", __func__, buf);
+}

lib/thread.h

@@ -230,6 +230,9 @@ extern pthread_key_t thread_current;
 extern char *thread_timer_to_hhmmss(char *buf, int buf_size,
 		struct thread *t_timer);
 
+/* Debug signal mask */
+void debug_signals(const sigset_t *sigs);
+
 #ifdef __cplusplus
 }
 #endif