virt plugin: Fix segfaults on shutdown

If connection has failed then `lv_init' returns early without initializing `notif_thread'.
This causes segfault due to incorrect `pthread_join()` call on Collectd shutdown.

Closes: #3082

diff --git a/src/virt.c b/src/virt.c
index d44aeb7..00227dd 100644 (file)
--- a/src/virt.c
+++ b/src/virt.c
@@ -2059,7 +2059,9 @@ static int start_event_loop(virt_notif_thread_t *thread_data) {
   if (pthread_create(&thread_data->event_loop_tid, NULL, event_loop_worker,
                      thread_data)) {
     ERROR(PLUGIN_NAME " plugin: failed event loop thread creation");
+    virt_notif_thread_set_active(thread_data, 0);
     virConnectDomainEventDeregisterAny(conn, thread_data->domain_event_cb_id);
+    thread_data->domain_event_cb_id = -1;
     return -1;
   }
 
@@ -2068,13 +2070,18 @@ static int start_event_loop(virt_notif_thread_t *thread_data) {
 
 /* stop event loop thread and deregister callback */
 static void stop_event_loop(virt_notif_thread_t *thread_data) {
-  /* stopping loop and de-registering event handler*/
-  virt_notif_thread_set_active(thread_data, 0);
-  if (conn != NULL && thread_data->domain_event_cb_id != -1)
-    virConnectDomainEventDeregisterAny(conn, thread_data->domain_event_cb_id);
+  /* Stopping loop */
+  if (virt_notif_thread_is_active(thread_data)) {
+    virt_notif_thread_set_active(thread_data, 0);
+    if (pthread_join(notif_thread.event_loop_tid, NULL) != 0)
+      ERROR(PLUGIN_NAME " plugin: stopping notification thread failed");
+  }
 
-  if (pthread_join(notif_thread.event_loop_tid, NULL) != 0)
-    ERROR(PLUGIN_NAME " plugin: stopping notification thread failed");
+  /* ... and de-registering event handler */
+  if (conn != NULL && thread_data->domain_event_cb_id != -1) {
+    virConnectDomainEventDeregisterAny(conn, thread_data->domain_event_cb_id);
+    thread_data->domain_event_cb_id = -1;
+  }
 }
 
 static int persistent_domains_state_notification(void) {