MEDIUM: mworker: reexec in waitpid mode after successful loading

Use the waitpid mode after successfully loading the configuration, this
way the memory will be freed in the master, and will preserve the memory.

This will be useful when doing a reload with a configuration which has
large maps or a lot of SSL certificates, avoiding an OOM because too
much memory was allocated in the master.

src/haproxy.c

@@ -690,7 +690,7 @@ static void get_cur_unixsocket()
  * When called, this function reexec haproxy with -sf followed by current
  * children PIDs and possibly old children PIDs if they didn't leave yet.
  */
-void mworker_reload()
+static void mworker_reexec()
 {
 	char **next_argv = NULL;
 	int old_argc = 0; /* previous number of argument */
@@ -791,6 +791,19 @@ void mworker_reload()
 	return;
 }
 
+/* reexec haproxy in waitmode */
+static void mworker_reexec_waitmode()
+{
+	setenv("HAPROXY_MWORKER_WAIT_ONLY", "1", 1);
+	mworker_reexec();
+}
+
+/* reload haproxy and emit a warning */
+void mworker_reload()
+{
+	mworker_reexec();
+}
+
 static void mworker_loop()
 {
 
@@ -801,7 +814,6 @@ static void mworker_loop()
 	/* Busy polling makes no sense in the master :-) */
 	global.tune.options &= ~GTUNE_BUSY_POLLING;
 
-	master = 1;
 
 	signal_unregister(SIGTTIN);
 	signal_unregister(SIGTTOU);
@@ -847,11 +859,9 @@ void reexec_on_failure()
 {
 	if (!atexit_flag)
 		return;
-
-	setenv("HAPROXY_MWORKER_WAIT_ONLY", "1", 1);
-
 	ha_warning("Reexecuting Master process in waitpid mode\n");
-	mworker_reload();
+	usermsgs_clr(NULL);
+	mworker_reexec_waitmode();
 }
 
 
@@ -3232,6 +3242,7 @@ int main(int argc, char **argv)
 
 		if (in_parent) {
 			if (global.mode & (MODE_MWORKER|MODE_MWORKER_WAIT)) {
+				master = 1;
 
 				if ((!(global.mode & MODE_QUIET) || (global.mode & MODE_VERBOSE)) &&
 					(global.mode & MODE_DAEMON)) {
@@ -3243,7 +3254,14 @@ int main(int argc, char **argv)
 					global.mode |= MODE_QUIET; /* ensure that we won't say anything from now */
 				}
 
-				mworker_loop();
+				if (global.mode & MODE_MWORKER_WAIT) {
+					/* only the wait mode handles the master CLI */
+					mworker_loop();
+				} else {
+
+					/* if not in wait mode, reload in wait mode to free the memory */
+					mworker_reexec_waitmode();
+				}
 				/* should never get there */
 				exit(EXIT_FAILURE);
 			}