qemu: Make sure qemuProcessStart is run within a job

qemuProcessStart expects to be run with a job already set and every
caller except for qemuMigrationPrepareAny use it correctly. This bug can
be observed in libvirtd logs during incoming migration as

    warning : qemuDomainObjEnterMonitorInternal:979 : This thread seems
    to be the async job owner; entering monitor without asking for a
    nested job is dangerous

src/qemu/qemu_domain.c

@@ -881,6 +881,29 @@ int qemuDomainObjBeginAsyncJob(virQEMUDriverPtr driver,
                                          asyncJob);
 }
 
+int
+qemuDomainObjBeginNestedJob(virQEMUDriverPtr driver,
+                            virDomainObjPtr obj,
+                            enum qemuDomainAsyncJob asyncJob)
+{
+    qemuDomainObjPrivatePtr priv = obj->privateData;
+
+    if (asyncJob != priv->job.asyncJob) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("unexpected async job %d"), asyncJob);
+        return -1;
+    }
+
+    if (priv->job.asyncOwner != virThreadSelfID()) {
+        VIR_WARN("This thread doesn't seem to be the async job owner: %d",
+                 priv->job.asyncOwner);
+    }
+
+    return qemuDomainObjBeginJobInternal(driver, obj,
+                                         QEMU_JOB_ASYNC_NESTED,
+                                         QEMU_ASYNC_JOB_NONE);
+}
+
 
 /*
  * obj must be locked before calling
@@ -955,17 +978,7 @@ qemuDomainObjEnterMonitorInternal(virQEMUDriverPtr driver,
     qemuDomainObjPrivatePtr priv = obj->privateData;
 
     if (asyncJob != QEMU_ASYNC_JOB_NONE) {
-        if (asyncJob != priv->job.asyncJob) {
+        if (qemuDomainObjBeginNestedJob(driver, obj, asyncJob) < 0)
-            virReportError(VIR_ERR_INTERNAL_ERROR,
-                           _("unexpected async job %d"), asyncJob);
-            return -1;
-        }
-        if (priv->job.asyncOwner != virThreadSelfID())
-            VIR_WARN("This thread doesn't seem to be the async job owner: %d",
-                     priv->job.asyncOwner);
-        if (qemuDomainObjBeginJobInternal(driver, obj,
-                                          QEMU_JOB_ASYNC_NESTED,
-                                          QEMU_ASYNC_JOB_NONE) < 0)
             return -1;
         if (!virDomainObjIsActive(obj)) {
             virReportError(VIR_ERR_OPERATION_FAILED, "%s",

src/qemu/qemu_domain.h

@@ -192,6 +192,10 @@ int qemuDomainObjBeginAsyncJob(virQEMUDriverPtr driver,
                                virDomainObjPtr obj,
                                enum qemuDomainAsyncJob asyncJob)
     ATTRIBUTE_RETURN_CHECK;
+int qemuDomainObjBeginNestedJob(virQEMUDriverPtr driver,
+                                virDomainObjPtr obj,
+                                enum qemuDomainAsyncJob asyncJob)
+    ATTRIBUTE_RETURN_CHECK;
 
 bool qemuDomainObjEndJob(virQEMUDriverPtr driver,
                          virDomainObjPtr obj)

src/qemu/qemu_migration.c

@@ -2118,6 +2118,10 @@ qemuMigrationPrepareAny(virQEMUDriverPtr driver,
         goto endjob;
     }
 
+    if (qemuDomainObjBeginNestedJob(driver, vm,
+                                    QEMU_ASYNC_JOB_MIGRATION_IN) < 0)
+        goto endjob;
+
     /* Start the QEMU daemon, with the same command-line arguments plus
      * -incoming $migrateFrom
      */
@@ -2126,9 +2130,8 @@ qemuMigrationPrepareAny(virQEMUDriverPtr driver,
                          VIR_QEMU_PROCESS_START_PAUSED |
                          VIR_QEMU_PROCESS_START_AUTODESTROY) < 0) {
         virDomainAuditStart(vm, "migrated", false);
-        /* Note that we don't set an error here because qemuProcessStart
+        if (qemuDomainObjEndJob(driver, vm) < 0)
-         * should have already done that.
+            vm = NULL;
-         */
         goto endjob;
     }
 
@@ -2235,7 +2238,7 @@ stop:
     qemuProcessStop(driver, vm, VIR_DOMAIN_SHUTOFF_FAILED, 0);
 
 endjob:
-    if (!qemuMigrationJobFinish(driver, vm)) {
+    if (vm && !qemuMigrationJobFinish(driver, vm)) {
         vm = NULL;
     }
     goto cleanup;