[evolution-ews] Autodiscover can cause deadlock in GCancellable code

[Milan Crha <mcrha src gnome org>]

commit 9b73c564aa78a34bc5b279771ab2221f23e2c123
Author: Milan Crha <mcrha redhat com>
Date:   Wed Nov 30 19:28:50 2016 +0100

    Autodiscover can cause deadlock in GCancellable code
    
    Reported downstream as:
    https://bugzilla.redhat.com/show_bug.cgi?id=1398531

 src/server/e-ews-connection.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)
---
diff --git a/src/server/e-ews-connection.c b/src/server/e-ews-connection.c
index c4f2f4c..40a9fbe 100644
--- a/src/server/e-ews-connection.c
+++ b/src/server/e-ews-connection.c
@@ -2452,7 +2452,6 @@ struct _autodiscover_data {
 static void
 autodiscover_data_free (struct _autodiscover_data *ad)
 {
-       g_object_unref (ad->cnc);
        xmlOutputBufferClose (ad->buf);
 
        if (ad->cancellable != NULL) {
@@ -2460,6 +2459,14 @@ autodiscover_data_free (struct _autodiscover_data *ad)
                g_object_unref (ad->cancellable);
        }
 
+       /* Unref the connection after the cancellable is disconnected,
+          to avoid race condition when the connection is freed inside
+          the g_cancellable_disconnect() function, which holds the
+          cancellable lock and blocks all other threads, while at
+          the same time the connection can wait for the finish of
+          its worker thread. */
+       g_object_unref (ad->cnc);
+
        g_free (ad->as_url);
        g_free (ad->oab_url);