upstream_conn: clean up keepalive event in sync case

Resolves this issue: fluent#6821

Signed-off-by: Wesley Pettit <wppttt@amazon.com>

include/fluent-bit/flb_upstream_conn.h

@@ -46,6 +46,9 @@ struct flb_upstream_conn {
     /* Keepalive */
     int ka_count;        /* how many times this connection has been used */
 
+     /* do we need to mk_event_del the keepalive event on clean up*/
+    int ka_dropped_event_added;
+
     /*
      * Custom 'error' for the connection file descriptor. Commonly used to
      * specify a reason for an exception that was generated locally: consider

src/flb_upstream.c

@@ -429,7 +429,7 @@ static int prepare_destroy_conn(struct flb_upstream_conn *u_conn)
     flb_trace("[upstream] destroy connection #%i to %s:%i",
               u_conn->fd, u->tcp_host, u->tcp_port);
 
-    if (u->flags & FLB_IO_ASYNC) {
+    if (u->flags & FLB_IO_ASYNC || u_conn->ka_dropped_event_added == FLB_TRUE) {
         mk_event_del(u_conn->evl, &u_conn->event);
     }
 
@@ -514,6 +514,8 @@ static struct flb_upstream_conn *create_conn(struct flb_upstream *u)
     conn->net_error     = -1;
     conn->busy_flag     = FLB_TRUE;
 
+    conn->ka_dropped_event_added = FLB_FALSE;
+
     /* retrieve the event loop */
     evl = flb_engine_evl_get();
     conn->evl = evl;
@@ -769,6 +771,7 @@ int flb_upstream_conn_release(struct flb_upstream_conn *conn)
                       conn->fd, conn->u->tcp_host, conn->u->tcp_port);
             return prepare_destroy_conn_safe(conn);
         }
+        conn->ka_dropped_event_added = FLB_TRUE;
 
         flb_debug("[upstream] KA connection #%i to %s:%i is now available",
                   conn->fd, conn->u->tcp_host, conn->u->tcp_port);