diff options
authorDaniel P. Berrange <>2012-09-26 15:54:58 +0100
committerDoug Goldstein <>2012-10-05 13:26:16 -0500
commit566d84c2b1ec22bc1916a2c665184e3466675b43 (patch)
parentnetwork: fix dnsmasq/radvd binding to IPv6 on recent kernels (diff)
Fix (rare) deadlock in QEMU monitor callbacks
Some users report (very rarely) seeing a deadlock in the QEMU monitor callbacks Thread 10 (Thread 0x7fcd11e20700 (LWP 26753)): #0 0x00000030d0e0de4d in __lll_lock_wait () from /lib64/ #1 0x00000030d0e09ca6 in _L_lock_840 () from /lib64/ #2 0x00000030d0e09ba8 in pthread_mutex_lock () from /lib64/ #3 0x00007fcd162f416d in virMutexLock (m=<optimized out>) at util/threads-pthread.c:85 #4 0x00007fcd1632c651 in virDomainObjLock (obj=<optimized out>) at conf/domain_conf.c:14256 #5 0x00007fcd0daf05cc in qemuProcessHandleMonitorDestroy (mon=0x7fcccc0029e0, vm=0x7fcccc00a850) at qemu/qemu_process.c:1026 #6 0x00007fcd0db01710 in qemuMonitorDispose (obj=0x7fcccc0029e0) at qemu/qemu_monitor.c:249 #7 0x00007fcd162fd4e3 in virObjectUnref (anyobj=<optimized out>) at util/virobject.c:139 #8 0x00007fcd0db027a9 in qemuMonitorClose (mon=<optimized out>) at qemu/qemu_monitor.c:860 #9 0x00007fcd0daf61ad in qemuProcessStop (driver=driver@entry=0x7fcd04079d50, vm=vm@entry=0x7fcccc00a850, reason=reason@entry=VIR_DOMAIN_SHUTOFF_DESTROYED, flags=flags@entry=0) at qemu/qemu_process.c:4057 #10 0x00007fcd0db323cf in qemuDomainDestroyFlags (dom=<optimized out>, flags=<optimized out>) at qemu/qemu_driver.c:1977 #11 0x00007fcd1637ff51 in virDomainDestroyFlags ( domain=domain@entry=0x7fccf00c1830, flags=1) at libvirt.c:2256 At frame #10 we are holding the domain lock, we call into qemuProcessStop() to cleanup QEMU, which triggers the monitor to close, which invokes qemuProcessHandleMonitorDestroy() which tries to obtain the domain lock again. This is a non-recursive lock, hence hang. Since qemuMonitorPtr is a virObject, the unref call in qemuProcessHandleMonitorDestroy no longer needs mutex protection. The assignment of priv->mon = NULL, can be instead done by the caller of qemuMonitorClose(), thus removing all need for locking. Signed-off-by: Daniel P. Berrange <>
1 files changed, 5 insertions, 10 deletions
diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index ec312d15c..f67495f34 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -1018,17 +1018,10 @@ no_memory:
-static void qemuProcessHandleMonitorDestroy(qemuMonitorPtr mon,
+static void qemuProcessHandleMonitorDestroy(qemuMonitorPtr mon ATTRIBUTE_UNUSED,
virDomainObjPtr vm)
- qemuDomainObjPrivatePtr priv;
- virDomainObjLock(vm);
- priv = vm->privateData;
- if (priv->mon == mon)
- priv->mon = NULL;
- if (virObjectUnref(vm))
- virDomainObjUnlock(vm);
+ virObjectUnref(vm);
static int
@@ -4048,8 +4041,10 @@ void qemuProcessStop(struct qemud_driver *driver,
priv->agentError = false;
- if (priv->mon)
+ if (priv->mon) {
+ priv->mon = NULL;
+ }
if (priv->monConfig) {
if (priv->monConfig->type == VIR_DOMAIN_CHR_TYPE_UNIX)