Restore SIGCHLD signal handler after being replaced by libuv (#9107)

daemon/main.c

@@ -1384,6 +1384,14 @@ int main(int argc, char **argv) {
 
     // fork the spawn server
     spawn_init();
+    /*
+     * Libuv uv_spawn() uses SIGCHLD internally:
+     * https://github.com/libuv/libuv/blob/cc51217a317e96510fbb284721d5e6bc2af31e33/src/unix/process.c#L485
+     * and inadvertently replaces the netdata signal handler which was setup during initialization.
+     * Thusly, we must explicitly restore the signal handler for SIGCHLD.
+     * Warning: extreme care is needed when mixing and matching POSIX and libuv.
+     */
+    signals_restore_SIGCHLD();
 
     // ------------------------------------------------------------------------
     // initialize rrd, registry, health, rrdpush, etc.

daemon/signals.c

@@ -111,6 +111,21 @@ void signals_init(void) {
     }
 }
 
+void signals_restore_SIGCHLD(void)
+{
+    struct sigaction sa;
+
+    if (reaper_enabled == 0)
+        return;
+
+    sa.sa_flags = 0;
+    sigfillset(&sa.sa_mask);
+    sa.sa_handler = signal_handler;
+
+    if(sigaction(SIGCHLD, &sa, NULL) == -1)
+        error("SIGNAL: Failed to change signal handler for: SIGCHLD");
+}
+
 void signals_reset(void) {
     struct sigaction sa;
     sigemptyset(&sa.sa_mask);

daemon/signals.h

@@ -6,6 +6,7 @@
 extern void signals_init(void);
 extern void signals_block(void);
 extern void signals_unblock(void);
+extern void signals_restore_SIGCHLD(void);
 extern void signals_reset(void);
 extern void signals_handle(void) NORETURN;