commit 86cae503a4404e068a11285564a0ee3862d1570c
Author: Daniel P. Berrangé <berrange@redhat.com>
Date:   Tue Mar 6 17:56:57 2018 +0000

    rpc: avoid crashing in pre-exec if no workers are present
    
    If max_workers is set to zero, then the worker thread pool won't be
    created, so when serializing state for pre-exec we must set various
    parameters to zero.
    
    Reviewed-by: John Ferlan <jferlan@redhat.com>
    Reviewed-by: Jim Fehlig <jfehlig@suse.com>
    Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

Index: libvirt-4.1.0/src/rpc/virnetserver.c
===================================================================
--- libvirt-4.1.0.orig/src/rpc/virnetserver.c
+++ libvirt-4.1.0/src/rpc/virnetserver.c
@@ -580,18 +580,21 @@ virJSONValuePtr virNetServerPreExecResta
         goto error;
 
     if (virJSONValueObjectAppendNumberUint(object, "min_workers",
+                                           srv->workers == NULL ? 0 :
                                            virThreadPoolGetMinWorkers(srv->workers)) < 0) {
         virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                        _("Cannot set min_workers data in JSON document"));
         goto error;
     }
     if (virJSONValueObjectAppendNumberUint(object, "max_workers",
+                                           srv->workers == NULL ? 0 :
                                            virThreadPoolGetMaxWorkers(srv->workers)) < 0) {
         virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                        _("Cannot set max_workers data in JSON document"));
         goto error;
     }
     if (virJSONValueObjectAppendNumberUint(object, "priority_workers",
+                                           srv->workers == NULL ? 0 :
                                            virThreadPoolGetPriorityWorkers(srv->workers)) < 0) {
         virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                        _("Cannot set priority_workers data in JSON document"));