Re: [libvirt] [PATCH 2/2] Fix monitor ref counting when adding event handle

From: Jiri Denemark <jdenemar(a)redhat.com&gt; 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 files changed, 10 insertions(+), 1 deletions(-) diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c index abf1338..7517e39 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);