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.

diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
index abf13383a8020f06dcbeecacedcb1f6a090826f5..7517e3999add874c4cbbf66c9a49dec89f53cfda 100644 (file)
--- 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);