From d84bb6d6a3bd2fdd530184cc9743249ebddbee71 Mon Sep 17 00:00:00 2001
From: Jiri Denemark <jdenemar@redhat.com>
Date: Wed, 12 May 2010 11:50:52 +0200
Subject: [PATCH] Fix monitor ref counting when adding event handle

When closing a monitor using qemuMonitorClose(), we are aware of
the possibility the monitor is still being used somewhere:

    /* NB: ordinarily one might immediately set mon->watch to -1
     * and mon->fd to -1, but there may be a callback active
     * that is still relying on these fields being valid. So
     * we merely close them, but not clear their values and
     * use this explicit 'closed' flag to track this state */

but since we call virEventAddHandle() on that monitor without increasing
its ref counter, the monitor is still freed which makes possible users
of it quite unhappy. The unhappiness can lead to a hang if qemuMonitorIO
tries to lock mutex which no longer exists.
---
 src/qemu/qemu_monitor.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
index abf13383a8..7517e3999a 100644
--- a/src/qemu/qemu_monitor.c
+++ b/src/qemu/qemu_monitor.c
@@ -223,6 +223,14 @@ int qemuMonitorUnref(qemuMonitorPtr mon)
     return mon->refs;
 }
 
+static void
+qemuMonitorUnwatch(void *monitor)
+{
+    qemuMonitorPtr mon = monitor;
+
+    qemuMonitorLock(mon);
+    qemuMonitorUnref(mon);
+}
 
 static int
 qemuMonitorOpenUnix(const char *monitor)
@@ -648,11 +656,12 @@ qemuMonitorOpen(virDomainObjPtr vm,
                                         VIR_EVENT_HANDLE_ERROR |
                                         VIR_EVENT_HANDLE_READABLE,
                                         qemuMonitorIO,
-                                        mon, NULL)) < 0) {
+                                        mon, qemuMonitorUnwatch)) < 0) {
         qemuReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                         _("unable to register monitor events"));
         goto cleanup;
     }
+    qemuMonitorRef(mon);
 
     VIR_DEBUG("New mon %p fd =%d watch=%d", mon, mon->fd, mon->watch);
     qemuMonitorUnlock(mon);