qemu: migration: Don't crash on access to 'current' job

When a VM is destroyed while being migrated (waiting in
qemuMigrationSrcWaitForCompletion) the private object cleanup code frees
the 'current' job info. Since the migration code attempts to setup
various aspects of the current job even on failure this results into a
crash.

Job data is cleared in qemuDomainObjPrivateDataClear since commit
888aa4b6

Fix this by skipping all of the code which requires the qemu process to
be alive if the VM is not active any more.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJiri Denemark <jdenemar@redhat.com>

src/qemu/qemu_migration.c

@@ -3561,27 +3561,28 @@ qemuMigrationSrcRun(virQEMUDriverPtr driver,
  error:
     orig_err = virSaveLastError();
 
-    if (cancel &&
-        priv->job.current->status != QEMU_DOMAIN_JOB_STATUS_QEMU_COMPLETED &&
-        virDomainObjIsActive(vm) &&
-        qemuDomainObjEnterMonitorAsync(driver, vm,
-                                       QEMU_ASYNC_JOB_MIGRATION_OUT) == 0) {
-        qemuMonitorMigrateCancel(priv->mon);
-        ignore_value(qemuDomainObjExitMonitor(driver, vm));
-    }
+    if (virDomainObjIsActive(vm)) {
+        if (cancel &&
+            priv->job.current->status != QEMU_DOMAIN_JOB_STATUS_QEMU_COMPLETED &&
+            qemuDomainObjEnterMonitorAsync(driver, vm,
+                                           QEMU_ASYNC_JOB_MIGRATION_OUT) == 0) {
+            qemuMonitorMigrateCancel(priv->mon);
+            ignore_value(qemuDomainObjExitMonitor(driver, vm));
+        }
 
-    /* cancel any outstanding NBD jobs */
-    if (mig && mig->nbd)
-        qemuMigrationSrcCancelDriveMirror(driver, vm, false,
-                                          QEMU_ASYNC_JOB_MIGRATION_OUT,
-                                          dconn);
+        /* cancel any outstanding NBD jobs */
+        if (mig && mig->nbd)
+            qemuMigrationSrcCancelDriveMirror(driver, vm, false,
+                                              QEMU_ASYNC_JOB_MIGRATION_OUT,
+                                              dconn);
+
+        if (priv->job.current->status != QEMU_DOMAIN_JOB_STATUS_CANCELED)
+            priv->job.current->status = QEMU_DOMAIN_JOB_STATUS_FAILED;
+    }
 
     if (iothread)
         qemuMigrationSrcStopTunnel(iothread, true);
 
-    if (priv->job.current->status != QEMU_DOMAIN_JOB_STATUS_CANCELED)
-        priv->job.current->status = QEMU_DOMAIN_JOB_STATUS_FAILED;
-
     goto cleanup;
 
  exit_monitor: