[libvirt] [PATCH] virnetdaemon: Don't deadlock when talking to D-Bus

[Michal Privoznik]

https://bugzilla.redhat.com/show_bug.cgi?id=1487322

In ace45e67abbd I've tried to fix a problem that we get the reply
to a D-Bus call while we were sleeping. In that case the callback
was never set. So I've changed the code that the callback is
called directly in this case. However, I hadn't realized that
since callback is called out of order it lock the virNetDaemon.
Exactly the very same virNetDaemon that we are dealing with right
now and have it locked already (in
virNetDaemonAddShutdownInhibition())

Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
 src/rpc/virnetdaemon.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/src/rpc/virnetdaemon.c b/src/rpc/virnetdaemon.c
index 00247cfc3..e3b9390af 100644
--- a/src/rpc/virnetdaemon.c
+++ b/src/rpc/virnetdaemon.c
@@ -439,14 +439,12 @@ virNetDaemonAutoShutdown(virNetDaemonPtr dmn,
 
 #if defined(WITH_DBUS) && defined(DBUS_TYPE_UNIX_FD)
 static void
-virNetDaemonGotInhibitReply(DBusPendingCall *pending,
-                            void *opaque)
+virNetDaemonGotInhibitReplyLocked(DBusPendingCall *pending,
+                                  virNetDaemonPtr dmn)
 {
-    virNetDaemonPtr dmn = opaque;
     DBusMessage *reply;
     int fd;
 
-    virObjectLock(dmn);
     dmn->autoShutdownCallingInhibit = false;
 
     VIR_DEBUG("dmn=%p", dmn);
@@ -470,11 +468,22 @@ virNetDaemonGotInhibitReply(DBusPendingCall *pending,
     virDBusMessageUnref(reply);
 
  cleanup:
-    virObjectUnlock(dmn);
     dbus_pending_call_unref(pending);
 }
 
 
+static void
+virNetDaemonGotInhibitReply(DBusPendingCall *pending,
+                            void *opaque)
+{
+    virNetDaemonPtr dmn = opaque;
+
+    virObjectLock(dmn);
+    virNetDaemonGotInhibitReplyLocked(pending, dmn);
+    virObjectUnlock(dmn);
+}
+
+
 /* As per: http://www.freedesktop.org/wiki/Software/systemd/inhibit */
 static void
 virNetDaemonCallInhibit(virNetDaemonPtr dmn,
@@ -516,7 +525,7 @@ virNetDaemonCallInhibit(virNetDaemonPtr dmn,
                                         25 * 1000) &&
         pendingReply) {
         if (dbus_pending_call_get_completed(pendingReply)) {
-            virNetDaemonGotInhibitReply(pendingReply, dmn);
+            virNetDaemonGotInhibitReplyLocked(pendingReply, dmn);
         } else {
             dbus_pending_call_set_notify(pendingReply,
                                          virNetDaemonGotInhibitReply,
-- 
2.13.5